Cowbirds in Nestboxes (Part 2)

In addition to Messages that have appeared in the Bluebird Mailing Lists on this topic, the following are on the Audubon Society of Omaha website:  Predators and Problems On The Bluebird Trail

Date: Wed, 24 Apr 2002 21:19:30 -0700 (PDT)
From: Bruce Johnson andyroooney"at"yahoo.com
Subject: Brown headed cowbird tries to adopt newly fledged bluebird?

Hello all -

Late this afternoon we had four bluebirds fledge from a box just off our back patio. As always my wife and I watched in awe as each one took their first flight.

It always seems that the air is electrified with the calling between the parents and babies.

Now to something I have never heard of, and the reason for this post:

A few minutes after the last fledgling had left the box and all had made it to a nearby tree, I saw a bird fly into the tree and immediately the adult bluebirds started attacking it. I feared for the safety of the fledglings. The unwelcome bird seemed to show absolutely no fear and seemed to ignore them.

When I finally got a good un-obstructed view of the situation, I saw this cowbird sitting right up against newly fledge bluebird on a branch, just like birds on a wire and acting as if it belonged there. When I say right up against, I mean just that. It appeared that their bodies were touching.

By this time the parents had ceased to attack but were still agitated. I succeeded in scaring the cowbird away and it did not return.

I would be interested to know if this is an extremely rare incident or if others have observed something like this.

Best regards,

Bruce Johnson
Life Mbr. NABS
Memphis, (extreme southwestern) TN

From: "Jacque Turner" turner"at"texasisp.com
Subject: Third Day Third Egg + One
Date: Tue, 30 Apr 2002 22:23:41 -0500

Today I checked my EABL nest and true to what some of you have said and what I have read, it's the third day of laying so there are three blue eggs plus one sparrow looking egg. I'm assuming it is not a HOSP egg or the three blue eggs would have been sabotaged. Does a BRHECO (Brown-Headed Cowbird is what I'm trying to say here) have an egg that looks HOSP-like? In the Peterson Western Bird Nests field guide the plate photo is too small to be very helpful. This egg is a short oval in shape & creamy white in color with brown dotted and spotted markings.

And right now I am wishing I had sized up the eggs better, but I think the EABL eggs may have been just a tiny bit larger than the spotted brown egg. Any experienced wisdom on this? Can I expect to see another odd ball egg tomorrow? 

My Bluebird Monitor's Guide is still loaned out. I am missing it for information like this and think tomorrow would be an excellent time to retrieve it!

Jacque Turner
Breckenridge, Texas

From: "Keith & Sandy Kridler" kridler"at"1starnet.com
Subject: Brown headed cowbird egg
Date: Wed, 1 May 2002 06:40:12 -0500

Keith Kridler Mt. Pleasant, Texas
The female brown headed cowbird can and does sometimes squeeze into a 1&1/2" round entrance hole. Is this egg in a box with the Peterson oval or a round hole, the oval is almost twice the square inch size of the round entrance so would make entering the nestbox easy for the Brown headed cowbird. In the past it was NOT unusual in northeast Texas to find cowbird eggs right below the round entrance hole of nestboxes laying on the ground. I figured that very possibly as the cowbird was squeezing into the nestbox her egg just popped out.

Bluebirds do have the capability of removing eggs with their beak without breaking the egg shell so some of these might have been removed by the female bluebird. I have never watched a bluebird remove a whole egg although others have witnessed this.

The cowbird eggs are very similar to house sparrow eggs in coloring and on average just a tiny bit larger than the sparrow or almost identical to the size of the bluebird eggs. There is a photo on page 27 in the Bluebird Monitor's Guide showing two cowbird eggs along with 4 bluebird eggs that I found in one of my nests. All eggs will vary slightly in shape, color and size between females of the same species so ANY photo is only a guide, yours may be darker or lighter than what is shown in the various books.

There is a very rare possibility that this egg is from another species of bird that dumped an egg in the box but the cowbird will hatch in about 9 days after incubation and will have a bright scarlet mouth lining to serve as a better target than the orange colored bluebird mouth. Remember that the birds that eat the most grow the fastest and the cowbird will have white fuzz instead of the black fuzz of a baby bluebird for the first couple of days.

An albino bluebird will also have white fuzz or hair like feathers right after they hatch. It would be nice scientifically to place this egg in a house Sparrow nest where eggs are just being laid to see if the competition affects the outcome of the sparrows successfully raising this young with theirs.

In bluebird nests the cowbird normally hatches 24 days before the bluebirds and will be 23 times the body weight of the bluebirds when they hatch several days later. Within about a day of the hatching of young birds the female will begin brooding the surviving young birds and not worry too much about eggs that begin to work their way into the nestcup.

In this nest one cowbird hatched on Monday, the second cowbird hatched on Tuesday the first bluebird hatched on Wednesday and the second cowbird was found dead in the nest under the older cowbird. On Thursday another bluebird hatched and then over the weekend a snake ate all of the surviving young birds and the two unhatched eggs. So the cowbird eggs made no difference in the outcome of this nesting attempt:-))) KK

From: "Lawrence Herbert" lherbert"at"4state.com
Subject: cowbird egg in house sparrow nest
Date: Sat, 4 May 2002 21:28:01 -0500

On April 22, 2002, I removed a House Sparrow nest and three eggs plus one Brown-headed Cowbird egg from a bluebird house. The House Sparrow was incubating. Nest hole is 1.5 inches diameter. This Eastern Bluebird trail is in Cherokee County, extreme southeastern, Kansas.

I would imagine that the cowbird would win out over the house sparrows if allowed to play out.

Good birding, Larry H., Joplin MO

Date: Sun, 9 Jun 2002 16:27:08 -0700 (PDT)
From: The Doctor sytyf"at"yahoo.com
Subject: what coolor are cowbird eggs?

I have a second EABL nesting where 1 of 5 blue eggs is larger than the rest. It is almost like a EUST egg.
 

Have a good day

Bob Sitarski a.k.a The Doctor, Jackson County Indiana ( 385244N 086023W ) & Clay County Illinois ( 384008N 0882908W )

Date: Sun, 09 Jun 2002 22:27:28 -0500
From: jacqueline tamm bjtamm"at"execpc.com
Subject: Re: what coolor are cowbird eggs?

If you know what a house sparrow egg looks like, you also know what a cowbird egg looks like, since the two are almost indistinguishable. That larger blue egg still could be a bluebird egg, since once in a great while, a bluebird will lay a "freak" egg. I've got a book called "Bluebirds" ( one book of a zillion ) written by Steve Grooms and Dick Peterson which has a picture of a normal and a freak egg side by side in a nest. (page 91, lower pic.) Bob T. Muskego, Wi., where besides four pair of bluebirds at my county park doing alot of bluebird producing, I now have a pair of bluebirds in my yard - 1st time in 10 years - and she is now incubating 5 eggs.

From: "Lawrence Herbert" lherbert"at"4state.com
Subject: bluebird/cowbird
Date: Thu, 4 Jul 2002 21:38:00 -0500

A cowbird was the first bird to fledge from the new bluebird trail in Newton County, extreme sw Missouri. Three bluebirds survived in that nest and were ready to fledge on July 1st.
Good birding, Larry H. Joplin MO.

From: "Lawrence Herbert" lherbert"at"4state.com
Subject: cowbird/bluebird
Date: Sat, 20 Jul 2002 21:43:27 -0500

One bluebird box in Cherokee County, Kansas, contained 4 bluebird eggs and one Brown-headed Cowbird nestling at either day one or two. The female was incubating when the nest was checked. This was on July 16.

On July 19 the nest contained four bluebirds at day two and no cowbird!

I speculate that the cowbird may have suffocated and died while the female bluebird was incubating the four eggs. The dead cowbird was then removed by the bluebird. Over the years I've had quite a few cowbirds but none have disappeared like this. Four bluebird eggs plus the one cowbird egg were were being incubated when the nest was checked on July 11, 2002.

Any thoughts on this? Larry Herbert, Joplin MO.

From: "Karen Louise Lippy" brdbrain"at"superpa.net
Subject: Re: cowbird/bluebird
Date: Sun, 21 Jul 2002 07:53:04 -0400

Lawrence,
Some birds recognize cowbird eggs and eject them from the nest or build another nest over top and lay again. Perhaps the bluebird did not recognize the egg, but did realize something was wrong when the chick hatched.

Another theory is that birds are stimulated to perform certain tasks as nesting proceeds. Perhaps the adults were not at the stage where they were 'programed' to begin feeding chicks, thus discarded the single hatchling in order to continue brooding the eggs.

Monitoring brings up some interesting things. The more we learn, the more we question what and why things happen as they do. People have been studying birds for 1,000's of years. You would think by now we would know everything there is to know. But for every question answered, 5 new questions emerge! Who says birding is dull!!!!!??????? Karen from South Central PA

Date: Wed, 24 Jul 2002 06:52:21 -0400
Subject: Re: Cowbirds
From: barbara chambers bj.chambers"at"verizon.net

on 7/23/02 8:58 PM, Karen Louise Lippy at brdbrain"at"superpa.net wrote:

I have been told that it is the song and call, that is genetic, that gets the cowbirds back together in the summer and fall. This is the way the male "recruits" . It had always been a mystery to me how they formed flocks and found each other by the fall and winter.

this year there are more cowbirds than usual in our area!

B.Chambers
Annandale/Fairfax VA

Cowbirds have a very interesting history. They once were confined to the mid-Western plains where they traveled with herds of buffalo feeding on insects kicked up by the large animals as they fed. Since the herds were constantly moving, the birds developed the habit of depositing eggs in other birds nests. Since the herds were rarely in the same location at the same time the next years nesting took place, little harm was done. Then we opened up the habitat and introduced domestic livestock. The "buffalo birds" now became cowbirds, but continued their parasitic nesting habits.

A female cowbird can lay as many as 30 eggs a season. She rarely lays more than one in a nest. They utilize many species as their hosts. Some birds recognize and remove the eggs or build nests over top and lay another clutch of eggs.

While the chicks usually hatch before the host species own, most times the adults can raise all of the birds. If several eggs have been laid in a nest (perhaps more than one cowbird selected this same host), they might outcompete the host species own chicks for food. An interesting bird which developed an ingenious method of reproduction. But because their numbers have increased greatly in some areas while some other bird species are declining at an alarming rate, cowbirds can be devastating to rare and endangered birds.

How does a cowbird know it is a cowbird since it is raised by another species? Studies seem to indicate that male cowbirds may recruit the chicks into flocks once they fledge and are capable of feeding themselves. Karen from South Central PA

From: "Keith & Sandy Kridler" kridler"at"1starnet.com
Subject: Re:cowbirds/trapping sparrows
Date: Wed, 24 Jul 2002 08:04:46 -0500

Keith Kridler Mt. Pleasant, Texas

Cowbirds: Baby cowbirds are a mouse brown/gray color until the males molt and get their black feathers. Some baby female bluebirds will look very black as they get their first feathers in but should have a distinct white eye ring and will develop a speckled breast. Starling young are also very brown/gray colored while in the nest and have a lot longer beak.

Now is the best time to use bait traps to catch large numbers of House Sparrows. The "young" sparrows of this year will look like adult females now, only the back corners of their beaks will be bright yellow. As their beaks "harden off" they will lose this yellow color. Felix may be catching more juvenile/female sparrows now as sometimes the adult males will continue to hang around nestboxes while the females are busy finding food for their just fledged young.

Kate has offered to draw a blueprint of the "two compartment" sparrow trap I have been using. Originally I made and used Joe Huber's style of sparrow traps in these boxes but made the drop bars out of aluminum and the trip wires out of 1/16" steel wire to make them less likely to trip when you trapped one sparrow in one compartment. A trapped sparrow can shake this box so much it will sometimes trip the second Huber trap.

About two years ago I replaced the Huber traps in these boxes with Floyd Van Ert's sparrow traps because they are less likely to prematurely trip in this style of trap box. I see a lot of sparrows when you install a trap of any style in a nestbox that the House Sparrows will come and scold you while you are at the nestbox checking "their" eggs/nest/babies and some are VERY wary of anything new. Very often one of the adults will be trapped in just a few minutes with the other watching either from the top of the box or from a nearby perch.

This "survivor" then see me go to the normal one holed trap box and remove their mate and reset the trap. Sometimes it will NEVER re-enter the nestbox as long as the trap is inside. By changing to different colored traps you can sometimes catch a sparrow in a gray or brown trap when the black one won't work. BUT by using a two compartment trap box installed over the front of the original box or by replacing the old box completely the "survivor" sees their mate enter the box and a door drop or snap shut. They hear their mate calling and quickly go to the box and look in the open compartment and see through the Plexiglas that their mate is unharmed but hopping just inches away from them and then they VERY often drop right into this open trap compartment. You now have caught BOTH of the troublesome sparrows with one trap setting!

IF you only see one trap door shut then you can safely open the other side of the box to look through the Plexiglas to see what you have trapped. When I install this two holed trap box over an active sparrow nestbox I normally remove some of the nesting material and replace it in the bottom of the trap box along with a couple of eggs in each compartment. Place them so that the sparrows can see their eggs when they look in the box.

Basically make two compartments that are about four inches square and the normal depth of your nestboxes. I cut or dado a saw kerfs thickness 1/2 way through the boards on the front back and bottom so that I can slide in a piece of Plexiglas (hardware cloth would also work) into this groove dividing the trap box. You now have a box that is about 9&1/2 inches wide, 10" tall with the back extending above the flat top giving you a flange to attach this to the front of the "sparrow controlled" nestbox. I access the traps by having each side able to pivot open. The top is screwed on so that I can slide out the Plexiglas occasionally and wash it.

The reason this works so well on "Two Holed" nestboxes is that with these you must close up one of the holes when trapping sparrows and this changes the boxes. By using a two holed trap box it looks just like their original nestbox so you are not changing their box any on the outside. Since most of my trail boxes are weathered gray I used old weathered cedar to construct these trap boxes. Even in busy city parks I can go and "change out" a few boxes and not bother people using the park and they have NO clue I am removing House Sparrows.

The Van Ert Traps will work even if you use slot boxes and constructed "two slot" trap boxes or by making "extra wide" two holed Peterson or Andrew Troyer two holed trap boxes. The average person does not need these styles of trap boxes but I am sometimes 20 or 30 miles away from home while checking nestboxes and I don't want to make four or five trips to catch that last sparrow!

The House Sparrow adults and young you remove today won't nest in your boxes next year! KK

From: Keith & Sandy Kridler [mailto:txbluebirder"at"sbcglobal.net]
Sent: Sunday, June 27, 2004 11:23 PM
Subject: cowbird just hatched Keith Kridler Mt. Pleasant, Texas

I got a decent picture of a baby cowbird that just hatched out this morning in a Carolina Wren nest in a Gilwood nestbox. The box was mounted 10 feet off of the ground and is the highest mounting location this species of wren has ever used for me and is the smallest nestbox size they have ever used. The picture shows one half of the cowbird egg still in the nest to show that cowbirds really do not adjust the color of their eggs to match the bird species they are parasitizing. This cowbird egg is larger than the Carolina wren eggs and the half egg shell had slipped over one of the wren eggs and I had to pull it off. Write to me off list if you want a copy of this as it shows the inside color of the mouth and the color and amount of "white fuzz". This is the 7th cowbird egg I have found this month in nestboxes and the third different species of cavity nester they have used. ... KK

From: Keith & Sandy Kridler [mailto:txbluebirder"at"sbcglobal.net]
Sent: Sunday, July 04, 2004 10:41 AM
Subject: cowbird growth and bluebird fledge times ... Cowbird in Wren nest.

Follows is the text that goes along with the 6th day picture of the cowbird in the wren nest. Notice the wording and know that this is not going to be a "happy" picture of a "happy" cowbird host family.

Nature is terribly cruel when it comes to survival of the "biggest" or most "powerful". It hurts to observe nature most of the time and not interfere! I deleted more than half of the names of those wanting the first photo's. I have photo's on 6-27 then 6-29 and 7-3 each two shot series is about 200 KB. For those wanting this series e-mail me privately but be patient for I need to pull temperature data loggers from about 20 nestboxes today and get ready for NABS trip. See you in Ithaca! KK

Text of 6-27 photo!Good morning everyone! Here is the 1 day old shot. I will go see if they survived to day 3. I did not realize so many would want to see a cowbird baby. I just LOVE their bushy eyebrows and they always have a "bad" hair day. Note the pieces of snake skin and moss in this nest. Because this nestbox is so small the wren did not build a typical "dome" over her nest. KK

This is a baby cowbird that just hatched this morning and there was still half of it's egg in the nest. The egg had slipped over one of the Carolina Wren eggs and I pulled it off to show the difference in the two colors of eggs. Note the color of the inside of the mouth is a brighter red than most baby birds. Notice the egg tooth right at the top end of the beak and how much white fuzz these baby birds have. This is the 7 th cowbird egg I found this month in nestboxes and I have two Carolina wrens in boxes now. Keith Kridler

Text of 6-29 cowbird photo! Notice the difference in the inside color of these birds mouths. The bigger red mouth makes a larger, brighter target. Something I have never seen or noticed before is that the cowbird at two days has it's eyes open and can discern movement. This means that when the baby Wren begs blindly that the cowbird will be able to see the adult wren and reach over the other baby and get more of the food. The cowbird is probably three times the weight of the wren already and will only get bigger. The wren was begging for food and the cowbird was SOO stuffed it could not even beg for food. I'll be gone for a few days and will send day five when we return. Keith Kridler

Text of 7-3 cowbird photo! You can see how big the cowbird is at 6 days old. It does not beg for food at a whistle any more as it's eyes were open on day two and it could respond to movement then. Now it immediately begs for food whenever there is movement near or over it's head. This pin feather stage is normally at about day 9 with baby bluebirds. Notice the feet on the cowbird! It was holding down two of the baby Wrens and you can tell by the body color of these two that one died about 12 hours ago and one of them under the foot had died early that day. The baby wren still alive had something wrong with it as it was continually gasping for air and could have been under the bigger cowbird when I lowered the nestbox down. Once again you can note the bright red mouth of the baby cowbird and what a good target this makes for a feeding parent. This was real hard to document this when I knew what the outcome was going to be. I was surprised to come back after three days and see that all three of the Wren eggs had hatched. Keith Kridler

From: Keith & Sandy Kridler [mailto:txbluebirder"at"sbcglobal.net]
Sent: Monday, July 05, 2004 11:38 PM
Subject: year of the Brown Headed Cowbird Keith Kridler Mt. Pleasant, Texas

I found four more cowbird eggs in nestboxes the past two days. One box tonight had three bluebird eggs and two cowbird eggs in it. This is the first time I have ever seen an egg that is more heavily spotted on the small end than the big end! I did not notice it at the time but in the photo it also looks like some of the dark spots from the cowbird egg rubbed off on the one bluebird egg. These were the lightest colored eggs from a cowbird that I recall seeing. So there is color variation between eggs in these birds:-)) ...KK

From: Lawrence Herbert [mailto:lherbert"at"4state.com]
Sent: Sunday, August 29, 2004 9:48 PM
Subject: cowbirds

Hoogy and all. Over the years I have had several cowbird eggs laid in bluebird houses here in se Kansas and sw Missouri. Female cowbirds can readily pass through a 1.5 inch hole. I wonder if cowbirds parasitize EABL more often than is noticed or is it a "local" thing - or a bit of both. At any rate EABL's behavior is to invariably "accept" the egg and raise the cowbird. We live right in the town of Joplin. I haven't observed an EABL at the bird baths in all of our years here. So, lucky you all that get to see the young come to the bath. This would be HOSP land. So I take our 60 boxes out into the country away from HOSP for the most part. Suburbs get closer to the nest boxes all of the time, however. I'll move the boxes rather than fight the HOSP. Good birding, Larry H. Joplin MO.

From: Dottie Roseboom [mailto:rosedot"at"mtco.com]
Sent: Sunday, August 29, 2004 11:20 PM

Re: cowbirds Larry, we have cowbirds, but have never seen one pay any attention to nestboxes. Thank goodness! I'm curious, as to why you would rather drive into the country than fight the sparrows? Do you dislike trapping or just think that it's easier not to? What will the established bluebird community do, if you remove the nestboxes AND they also have sparrows competing with them for natural cavities? BTW, I live in the country (I can hear cows "mooing" and roosters "crowing") and we still have sparrows. So pay attention to what area of the country that you move the nestboxes into. Dottie Roseboom Peoria IL (central - zone 5)

From: Keith & Sandy Kridler [mailto:txbluebirder"at"sbcglobal.net]
Sent: Monday, August 30, 2004 8:43 AM
Re:cowbirds Keith Kridler Mt. Pleasant, Texas

There was just a newspaper article online last month on cowbirds that said that they benefit from more host baby birds surviving in the nest. Most of the time when a cowbird egg is in a nest few if any of the other young survive that I have seen. Cowbirds laying in nestboxes in Northeast Texas is pretty common. They seem to use nestboxes with holes larger than 1&1/2" (Gilwood, slots, ETC.) more than the standard size. Very often an entrance hole drilled 1&1/2" does not stay that size for the life of the nestbox! I have seen the Brown-headed Cowbird eggs in PVC nestboxes with 1&1/2" holes and these do stay the same size they are drilled.

Sometimes cowbirds remove an egg when they lay one and I believe many times they do not remove a host bird egg. I watched a cowbird enter and later carry a bluebird egg out of a natural cavity once and she probably laid an egg in the cavity but the snag was 18' or more over water and about 30 feet from the shore line.

I found two pierced bluebird eggs near a nestbox and where there were four bluebird eggs there were now two and two of each species. Larry Zeleny reported cowbird eggs in nestboxes in Maryland. I have often found a "brown speckled egg" on the ground directly under the entrance hole of active bluebird nests. I always thought that the egg squirted out as the female cowbird tried to squeeze into the nestbox.

Tina Phillips mentioned that maybe the cowbirds backed up to the box front and dropped the egg through the hole from the outside. Few of these cowbird eggs dropping five feet into short grass are ever broken. Do a "few" Eastern Bluebirds pick up the foreign egg and remove them? Do the eggs "miss the entrance hole" or do a few get pitched out the door by Mama Bluebird! Do Cowbird eggs have thicker calcium layers than their host birds? HMMMM lots more research needed:-))) KK

From: Dottie Roseboom [mailto:rosedot"at"mtco.com]
Sent: Monday, August 30, 2004 11:55 AM
Subject: Re:cowbirds

Another interesting question to ask for future studies: Do cowbirds prefer nests in cavities, or the more open style robin's nest? If only we could train them to love starlings & sparrows' nests :-) Of course, some people in our area, relate the increase of cowbirds to deep woods destruction, as the cowbird prefers the woodland edge, rather than grasslands or forests. Guess that we are our worse enemy. I've found cowbirds to be an interesting species. But then, again, I don't have them invading nestboxes. (at least, not YET) Dottie Roseboom Peoria IL (central - zone 5)

From: Torrey
Sent: Thursday, January 20, 2005 1:43 PM
Subject: OT other "bad" birds

This may be just throwing more wood on the fire, but what about native (& therefore protected) birds with bad behavior?

This summer, nature center staff did nest-searching for forest birds at a nearby military training area.
Here are some of our results.

# of nests:  Wood Thrush 45, Hooded Warbler 33
# of nests with cowbird eggs:  WOTH 11, HOWA 26
% of nests parasitized:  WOTH 24%, HOWA 79%

Hooded Warblers are about the size of chickadees & are dwarfed by their cowbird nestlings.  Wood Thrush are about the same size, but cowbird eggs hatch earlier & the first thing the baby cowbird does is try to push eggs out of the nest.  Both of these species are suffering population declines.  (The whole guild of "deep forest" birds is.)

Brown-headed Cowbirds, tho, are native & protected by the migratory bird act.  Thay're an open grassland species that expanded its range when humans cut down all the forests.

It's easy to see how we can help bluebirds.  Any thoughts on how to help birds who nest in relatively inaccessible forest interiors?

=====
Torrey Moss
Kalamazoo Nature Center
Kalamazoo, MI

From: Dottie Roseboom [mailto:rosedot"at"mtco.com]
Sent: Thursday, January 20, 2005 6:12 PM
Subject: Re: OT other "bad" birds

Torrey, I'm glad that you mentioned the Cowbird. Several years ago, I read an article (by the Nature Conservancy, I believe) that described the breeding habits of the Cowbird. I never realized how complicated life was for this particular female. Imagine trying to be seductive and trying to find a suitable nursery so that an offspring that you'd never see could have life. If she is fertilized too early, she may have to "drop" the egg anywhere. If she selects an nest where its eggs will be hatching the next day, her egg will never be incubated. And so on. Because of such a complicated cycle, at one time the Cowbird numbers were extremely low in many parts of the country. They only use nests in "edge" habitat, not deep woods.The article's author had studied the volatility of the Cowbird population - it correlated with land development. He feels that the cowbird may now be impacting other song birds, but once again, the "devil" behind the scenes is man's thirst for land. The Cowbird has been here for eons without causing any major problems. Mother Nature has always provided an extra Wood Thrush or two for the Cowbird to displace. Tough, but it works. However Mother Nature can NOT reforest acres as quickly as we lumber/bulldoze./etc.  When we stop destroying the "Deep Forests", the Cowbird numbers will stop rising. Reminds me of the Ivory-Billed Woodpeckers last stand.
    Dottie Roseboom
    Peoria    IL    (central - zone 5)

Keith Kridler Mt. Pleasant, Texas
In the spring the female cowbird begins searching out nests to lay her eggs in. There is a very small time window during egg laying and before incubation starts that she needs to hit so that her eggs will hatch. They are VERY good at this from the numbers of cowbirds reported in the USA.

You will often see 3>5 male cowbirds singing and following her where ever she flies. The males never seem to help her locate a bird nest. I finally caught a female cowbird last summer inspecting a Carolina Wren nest wedged between two large tree plant buckets. The nest was only two feet off of the ground and there were four eggs. I went back for a week expecting to find a cowbird egg in the nest. I never expected the Carolina Wrens to fledge from this poorly located nest but they did. I failed to feel the wren eggs to see if they were warm or being incubated. Does the cowbird feel the eggs for warmth? Can she count and remember if there were fewer eggs yesterday in this nest?

About 300 feet from this Wren nest another Carolina Wren nested in a Gillwood box and IT was parasitized by the Cowbird. The Cowbird fledged but all of the baby wrens perished one by one as they hatched out later than the cowbird and could not compete for food. The Gilwood box is the one with the wire running across the larger entrance hole.

If anyone traps cowbirds while trapping House Sparrows or Starlings then see if they can escape a normal "bluebird" nestbox with a 1&3/8" entrance hole.
This is 1/8" smaller than a normal bluebird nestbox but most birds can squeeze out of a smaller hole than they will squeeze into while laying eggs.
KK

Here are some excerpts from the Brown-headed Cowbird article by Peter E. Lowther in "The Birds of North America", a series put out by the Academy of Natural Sciences & the American Ornithologists' Union.
* ~ * ~ * ~ * ~ *

Over 220 host species have been reported as being parasitized (= cowbird "victims"); 144 species have actually reared cowbird young (= cowbird hosts). Cowbird hosts range in size from 10 gram creepers, kinglets, or gnatcatchers to 150 gram meadowlarks.

Cowbirds find nests in three ways: female may perch quietly in the tops of shrubs or trees and silently watch for nest building activity in surrounding open areas; female may walk on ground, looking about and watching movements of other birds; or female may employ a noisy searching method of short flights between vegetation with landings in leaves accompanied with wing flapping as if intentionally trying to flush potential hosts from nests.

Egg dates: beginning mid- to late April until mid-July.

Cowbirds lay "sequences" of 1-7 eggs with intervening "pauses" of 2 days throught the breeding season.

With adequate nutrition, females lay almost daily during the breeding season. ... Females may lay about 40 eggs/season. ... One [captive] female laid on 32 consecutive days her first year and 77 eggs in her second year, including 67 eggs in one sequence.

Feeding rates to cowbird fledglings vary, depending on host species, but always higher than feeding rate for hosts' own young.

[Fledgling] independence -- at 16-28 days out of nest.

* ~ * ~ * ~ * ~ *
This article was published in 1993. "The Birds of North America" series is very in-depth & informative, but very dry. I tried to pick out quotes that were to-the-point & interesting.

One fact that didn't have a nice easy quote: Female egg-laying ranges overlap, so a nest with 2 cowbird eggs was likely visited by 2 cowbirds. In the afternoon, cowbirds are more gregarious & congregate at feeding areas.

Also, Eastern Bluebirds were listed in the "feeding rates to fledglings" paragraph, but it didn't say if the nest was in a box or a natural cavity.

This is more than i ever wanted to know about cowbirds. Hope it helps. :-)

=====
Torrey Moss
Kalamazoo Nature Center
Kalamazoo, MI

Keith Kridler Mt. Pleasant, Texas
I have seen one female cowbird leave a natural cavity in a tree with a blue egg in her beak. The tree was about 75 feet out from the bank in a 3 acre lake. She flew past me about 20 feet away and dropped the egg so that it landed just out of my reach from the shore. Eastern Bluebirds had nested in that tree for several years as this was a favorite fishin' hole of mine.

On another occasion a cowbird removed two bluebird eggs and laid two of her eggs in a nestbox near some of our greenhouses. The cowbird flew directly away from the nestbox flying over one greenhouse and dropping both eggs on the second plastic covered house. Both bluebird eggs were laying about three feet from each other where they had rolled down the sides of the house.
Neither one had broken and each had two perfect < > where the cowbird had jabbed and then grasped the eggs with these small Chevrons that the beak made in the shells. I did NOT see any of this happen but when checking my records two blue eggs were removed and two speckled eggs were added and I hunted for the missing eggs. I blamed the cowbird even though I actually have no scientific proof. It would be neat to be able to check the DNA of two cowbirds eggs in a nest to see if they are related.

Since cowbirds are native and sometimes use cavities do we add them to the list of cavity nesters? Since they invade the nests of native birds and sometimes cause death should we label them "Native Invasive" species? :-))) It is amazing how many eggs they can lay a year when they don't have to feed or change their babies diapers! KK

I monitor breeding birds at one of our parks. We are in the "land of cowbirds" in central Illinois. During fledgling season I see many of our native birds feeding cowbird fledglings. I always see our native Song and Field Sparrows feeding them, especially early in the season. The bird who wins the prize for raising cowbirds around here is the Common Yellowthroat.

Last year my most interesting and disappointing sighting was seeing a very fat, well-fed cowbird balancing itself on the edge of an Orchard Oriole nest while it was being fed by oriole adults. Since Orchard Orioles are uncommon around here, my heart sank. One can walk around and hear the noisy cowbird fledglings begging on the ground even when you don't see them in the brush.
Alongside the HOSP, our native species have a lot to deal with! I have never seen a Bluebird feeding a cowbird. Hope I don't!

Charlene Anchor, Central Illinois

Charlene,

Last summer, I watched a tiny Chipping Sparrow frantically feeding a big fat Cowbird. She (or he) had to fly up off the branch just to reach it's big fat beak, then rush off to find more food.

Barbara Burnham
Ellicott City, MD

[In response to a question: We put up a new 48 hole Purple Martin mansion this year, and were surprised to see it being inhabited by cowbirds this morning! They just started building their nests, and chased away the purple martins that were checking it out! We really aren't terribly interested in providing either food or shelter to the rowdy cowbirds! What's the best way to shoo them on?]

Crescent holes on the martin houses should take care of the Cowbirds. By-the-way, I like Cowbirds. They are crazy and do funny things.

Dottie, Hickory Hollow
Brown County, Indiana

These are probably going to be European Starlings, Brown Headed Cowbirds
don't build their own nests. The Starling Resistant Entrance Hole is talked
about in the Bluebird Monitor's Guide. Draw a 3 inch diameter circle then
draw a straight line so that you create a crescent from this circle that is
only and precisely 1&3/16" tall. ANY higher and Starlings will be able to
enter your Martin House. Remember this is far smaller than some of the
"larger holed" bluebird nestboxes.

Common names for birds can be misleading as in this area the imported White
Cattle Egret is sometimes called a "cowbird".
Keith Kridler Mt. Pleasant, Texas

Brown-headed Cowbirds are brood parasites, that is, they have completely
abandoned the tasks of building nests, incubating eggs, and caring for
hatchlings. Instead, each female deposits as many as 40 eggs per year in
nests that belong to other bird species. More than 100 other species have
provided host nests for cowbird eggs. The female cowbird finds these nests
by watching patiently from an observation post where she can look down upon
grassland species, by observing the nests of tree-nesting species while she
walks quietly on the forest floor, or by crashing noisily through shrubbery
with flapping wings to flush out potential victims. She typically chooses a
nest with eggs smaller than her own and lays a single egg quickly at dawn
once the host has also started laying eggs. Unlike the parasitic European
cuckoos, Brown-headed Cowbirds do not evict their nest-mates, although the
female may remove and sometimes eat eggs from the host nest. Instead,
cowbird nestlings typically out-compete their smaller nest mates.

...

Crystal Hill~Georgia

Cowbird nestlings will sometimes push other eggs out, but it varies by location and situation.

On a good note, some species of songbirds are beginning to show signs of recognition when it comes to cowbird eggs. Not a fast process, but encouraging. --J

Is this a guard you put on the martin house holes?
Evelyn

It is a 'different' entrance designed to keep Starlings from entering. I only put these type of
entrances on my Martin houses.

As Dottie mentions, this should do the trick with cowbirds since they are about the same size.

Regards,
Glady's

If we find Cowbird eggs in a non-cowbird nest, is it OK to remove them (or are they protected)? I ask because I think I have seen Cowbirds in our yard, and want to be ready just in case.

Shawn in Sevierville, TN

From: bookfanaticef-bluebird "at"yahoo.com [mailto:bookfanaticef-bluebird "at"yahoo.com]
Sent: Thursday, April 14, 2005 11:00 PM
Subject: Re: Cowbirds Info

Shawn,
I would say NO--it's not legal to remove their eggs, because they are a native species, and all native species are protected from harassment (and other similar actions) by federal laws. Yes, they are "undesirable," but they are native birds, even if their range has become unnaturally expanded because of human activities. Only non-native species (i.e., House Sparrows, European Starlings, etc) can be legally removed and killed with no special permits required.

However, I also know that in some areas, BHCO control & eradication is frequently done--in fact, while looking for summer field jobs, I've come across many job postings where capture and killing of cowbirds is essentially the only duty. Please note, however, that these jobs were posted by state and federal wildlife or environment *government agencies,* so they have special permits to do this, and probably only in places (national wildlife refuges, etc) where recent cowbird invasions, and therefore brood parsitism by cowbirds, are threatening the survival of a listed (i.e., threatened or endangered) bird species they are trying to manage for.

Consult your local or state wildlife agency and see what they say to be sure, but the answer will most likely be NO.
Elizabeth Farley
Gainesville, FL

Shawn and others on cowbird issue,
In Texas, the brown-headed cowbird is present in large numbers due to the "windfall" created by the huge cattle industry, substituted for the historic buffalo herds the cowbirds used to follow and
depend upon.

It is perfectly legal to control cowbirds by trapping, egg destruction, etc. and many landowners have state approved trapping programs. The impetus for this was the steady decline in certain songbird species such as black-capped vireos and golden-cheeked warlbers, now on the endangered list. On government refuges, cowbird parasitism was found to be a major factor in the declines of vireos
and intensive control of cowbirds through trapping significantly improved nestiing success

So you should probably find out your own state laws. Here, they are legally controlled. (Although it hasn't seemed to change the fact that significant numbers still visit my property each year about this time looking for nests to use).
Jim Garriott
San Antonio, TX

From: david calhoun [mailto:dlcdmd"at"bellsouth.net]
Sent: Wednesday, April 27, 2005 7:03 AM
Subject: getting rid of cowbird egg

I have a cowbird egg in my bb nest.(Am positive isn't bluebird-white with brown speckles.)Should I remove it, or will that upset mom and maybe make her abandon nest? Just poke a pinhole instead?Thanks.David Calhoun,Louisville,Ky.

Keith Kridler Mt. Pleasant, Texas
HMMM this is a good question! Kind of like when you find and endangered species getting ready to eat another endangered species for food:-))

Cowbirds are native and probably fall under the protection of migratory bird act. There are some species that will remove the cowbird egg themselves and some will build a new nest and lay new eggs over this cowbird egg.

I have found that most bluebirds will attempt to incubate and then feed this cowbird to be. To be safe you could mark the egg and carefully move it to a House Sparrow nest. (I just gave Tina Phillips a heart attack:-))

Cowbird eggs hatch in 9 days, bluebird eggs hatch in 12 days. You will have a cowbird with a three day head start on native birds. Within a day of hatching the female will begin to split her time incubating with going in search of food. Eggs will cool more and more and incubation times lengthen for the remaining eggs. Bluebirds evolved so that when the eggs begin hatching they all hatch within 24>36 hours (or so) Any eggs still in the nest to a bluebird after 36 hours means that they will not hatch.

Bluebirds can and do remove young that die in the nest. Bluebirds can and do occasionally remove a runt from a nest. Cowbirds have a bright red mouth lining, bluebirds have an orange lining to their mouth. Cowbirds mouths make a more dramatic target for an adult bringing food to the nest. Less food to other birds creates less development.

Measure the entrance hole diameter on your nestbox precisely and report what this cowbird was able to enter and also the thickness of the front board.
Was the front "slick" planed wood, rough sawn, does it have a perch ETC.
What style nestbox. I would wait and see how long it takes for the cowbird to hatch or if it will hatch. Then record how many bluebirds hatch and add this data to the Cornell website.

You don't learn much from killing something but you have a rare chance to add scientific observations. If you have a digital camera you might want to take daily photos so see how the eggs are moved around in the nest every day by the female during incubation. KK

David and Bluebirdsters: I'm not going to answer your question, but read on anyway!

Over the years I've probably had about 10 or 12 cowbird eggs in EABL nests.
I don't have time to check my records but about half have raised the cowbird along with the bluebirds, about 1/4 raised just the cowbird at the expense of the bluebirds. A couple nests were abandoned. Not sure if the bluebirds were going to abandon anyway or they did it because of the cowbird egg. A predator got a couple others.

Good birding, Larry H. Joplin MO.

I caught four cowbirds in my sparrow trap yesterday. My husband went to let them out and one of the poor moms laid an egg, almost in his hand.

Dottie, Hickory Hollow
Brown County, Indiana

You sure do NOT want cow birds. They are parasites. Will lay an egg in an established nest and then when hatched, the baby will eat and starve the babies that should be fed. Terrible to see a little song sparrow feeding that huge baby constantly and not hardly eating for itself. Linda in NW GA

Carolina Wrens (CAWR) are native cavity nesters so I think this is on topic.
Here is an update on the CAWR nesting escapades at my house. I have now named this pair of CAWR's The Hell's Angels.

You may recall that they tried several times to make a nest in my husband's motorcycle helmet which had been placed on the top shelf in our garage with the visor open. I was greatly amused by this, but my husband was not. I removed the helmet nesting material and installed a CAWR box in the most sheltered corner of my front porch near the ceiling. I put their nesting material in there. They found the nest in a couple of days, quickly finished it, and laid 3 eggs that I am aware of. I have heard that these birds can be rather shy, so I left them alone until about a week ago.

I decided I had to check the progress of the nestlings. John Schuster might scold me heartily, but I got the ladder out of the garage so I could peer in the box. Inside the CAWR nest was one big chick. When I made a kissing noise, the chick opened its mouth and it was bright red. The chick was just getting its pin feathers and was already bigger than either of its "parents". It was one fat, healthy Cowbird chick! Yikes! I have named him Baby Huey.

He is fully feathered now although his tail feathers are too short to fly well. He flew out of his box yesterday when I was looking at him and perched in my Sergeant Crabapple tree. He is still there today and Mom and Dad CAWR love their little guy. He is bigger than they are and looks nothing like them, but they are truly the Hell's Angels when I get near, scolding me and raising quite a ruckus. When I am not right there, they are stuffing food in Huey's mouth and proudly singing. I think they believe they are parenting the biggest, most beautiful CAWR ever. I periodically check on him to say hello and The Hell's Angels scold me heartily. He quietly looks at me and blinks and he has a funny tuft of feathers that stick out of the top left side of his head.

The Hell's Angels are also going back into the garage again. I checked the motorcycle helmet and it is fine. I discovered what they are doing today.
They found the tupperware tub of mealworms on top of my refrigerator and are availing themselves of great quantities to feed Baby Huey.

Paula Z
Powell (Central) Ohio

From: LMHMDH"at"aol.com [mailto:LMHMDH"at"aol.com]
Sent: Tuesday, May 24, 2005 6:12 PM
Subject: strange egg in nest

This is our first year to put up a bluebird box and we checked it yesterday and found 4 light blue eggs and 1 egg that was offwhite with tan specks. It is the same size as the bluebird eggs and the bluebirds seem to be taking care of the eggs. I am guessing that something else got in there but I'm not sure what we should do about it. Do I try to remove the different egg? A link to a picture http://im1.shutterfly.com/procserv/47b5db05b3127cce919d405e4c3a00000016108Cbs27Rm1ZQ

Thanks for any advice.

Lara Hampton
Missouri

Lara in MO:

I'll guess that's a Brown-headed Cowbird egg.
Good birding, Larry H. Joplin MO.

From: bookfanaticef-bluebird"at"yahoo.com [mailto:bookfanaticef-bluebird"at"yahoo.com]
Sent: Tuesday, May 24, 2005 8:00 PM
To: LMHMDH"at"aol.com; Bluebird-L"at"cornell.edSubject: Re: strange egg in nest--cowbirds

Lara,
Even without seeing the picture, I would say with 95% certainty that what you have is a Brown-headed Cowbird (BHCO) egg in your nest. After seeing the picture, I was positive that's what it is--it sure looks like the cowbird eggs I have seen. I'd also guess that if you had checked the nest a few days ago, there would have been 1 more bluebird egg than was in your box yesterday--the number of total eggs would be the same, but a BHCO egg would have replaced the EABL egg.

More information on cowbirds, even though you may know this already, but maybe some people on the list do not. BHCO are obligate brood parasites, with the females laying their eggs in other birds' nests. Cowbirds never build their own nests. They often watch the host female to find her nest, then go in and lay their own egg, in many cases removing a host egg up to a day before or after they lay their own egg. A particular female BHCO will only lay one of her eggs in any given host nest, but sometimes more than one female cowbird will visit a host nest & lay their eggs in it. The eggs & chicks develop very quickly--about 10-13 days to hatch, and 10-11 days to fledge, which is faster than many of their hosts--and a couple days faster than bluebirds. This is so the chick can take advantage of being the largest in the nest, and get the most food. Unlike some other brood parasites, like the infamous Eurasian Cuckoos, cowbird chicks rarely&nbs! p;kill or eject the other eggs/young in the nest with them--however, they do sometimes outcompete the host young for food. However, parasitism by BHCO is not always successful--a lot depends on when the BHCO female lays her egg in the host nest. There is actually a very small window of time for her to do so if her egg is to hatch first and the nestling to successfully fledge. If she laid the egg after the host has started incubating, the egg will not hatch, or will hatch at the same time or later than the host eggs, and the BHCO chick will be either the same size or smaller than the host chicks, and it will lose its "competitive edge." This situation makes it more likely that all the host chicks will also survive to fledge, rather than one or more being lost to starvation.

Cowbird parasitism is a major problem for many host species, as they do not recognize the cowbird eggs/young as being different (despite a sometimes large difference in size and/or coloration), and raise them as their own, sometimes to the loss of their own eggs/young. IN areas with high densities of cowbirds, some "acceptor" species like many vireos and warblers can lose all of their eggs because they were replaced by cowbird eggs. Some species, on the other hand, do recognize the BHCO egg as different, and will eject or destroy the egg, or abandon that nest & start over again. Some species will build the new nest over the top of the old nest.

I do not know if BHCO parasitism is a major problem for bluebirds or not--perhaps they reject the eggs, at least sometimes, as some species are known to do. To my knowledge, cavity-nesters as a general rule are rare cowbird hosts, and therefore, I assume present only a minor problem for them--cowbirds frequently parasitize open-cup nesters, however. Despite high abundances of BHCO in the areas where my EABL boxes are, I have yet to see a cowbird egg in any of my nest boxes.

As BHCO are native species, in many places they are protected from interference by federal law, unless you have a special permit. HOWEVER, in some areas where they have become a major problem for agriculture or the populations of host species of birds, it is perfectly legal to remove & destroy cowbird eggs, nestlings, or adults without any permits. I recommend checking with your local wildlife agency or extension office to see what is legal in your area.
Good luck wiht your bluebirds!
Elizabeth F
Gainesville, FL

Hi Lara,

It's pretty neat that you've got a cowbird egg in your box. They rarely parasitize cavity nesters. (Out on the Plains, where they're from, it's mostly ground nesters.)

Cowbirds are heavier-bodied than bluebirds, so i'm kinda surprised she got in there to lay an egg.
Unless your hole is a little bigger than normal? Or maybe it was an extra-small cowbird. Or maybe she was very acrobatic & perched with her vent against the hole. :-) Songbirds are essentially adult size when they leave the nest -- I wonder if your visitor will be able to squeeze out when it's time to fledge.

You'll have an interesting season, i guess. :-)

yours, Torrey

Torrey Moss
Kalamazoo Nature Center
Kalamazoo, MI

Hi all,

Cowbirds can definitely get into a 1 1/2" nest box hole. I've had them lay eggs in my nest boxes, and just happened to see the female exiting once. The female cowbird is a little smaller than the male -- at least that's the case around here....

Mary Jane Shearer; Tucker, GA

Monitoring my trail in Newton County, sw Missouri, this morning, I found a Brown-headed Cowbird egg with four EABL eggs.
(Box # 01-05-TFRD). 06-09-05.
First of the year.

Last checked on 06-04-05: "BL nest no eggs," so cowbird egg will have
a huge head-start in this instance.

Good birding, Larry H. Joplin MO.

Amy and Bluebirdsters -

Brown-headed Cowbird eggs often look very similar to House Sparrow eggs and they are very similar in size too!

I found the second cowbird egg of the year on one of my trails today. It was in a Carolina Wren nest with six eggs.

Good birding, Larry H. Joplin MO.

Good morning. I went to the farm Sunday and found the behind near barn nestlings had fledged. I didn't get to see this but the time was right. The nest was flattened somewhat and fecal material was present high on the walls. I didn't see Mom and Pop, but their meal worms were missing I had placed in their bowl when I returned a couple of hours later.

The nest box above the pond, that had contained 3 bluebird eggs now contains 2 bluebird eggs and a large fledgling. The fledglings' head is about the size of one blue bird egg. I suspect a cowbird? But the third blue bird egg is missing. Do cowbirds remove an egg before they dump one? What must I do?

I am happy to report there are four blue bird eggs in the front yard nest box (where the nestlings disappeared earlier). The box is now on a pole approximately 15 feet from the fence and has a cone guard on it.

Lana Hunt
Morehead, KY

Lana in KY and Bluebirdsters:

Research has shown that Brown-headed Cowbirds regularly remove an egg from a nest.
Harry Hann (1941) found that "These are not removed at the time of laying, but during the forenoon of the previous day, or the day of laying, or rarely the following day."

Further: "The number of eggs removed from parasitized Oven-birds' nests was eighty-five per cent of the number of eggs laid..."

These observations were made with his study of the Ovenbird in Michigan.

Mrs Nice (1939) has twice seen a cowbird remove an egg from a song sparrow's nest, "the thief eating the egg and shell" in one case.

Having said this I think you have a bluebird nestling. But watch when the nestling begs for food. Maybe it's a bluebird if it has a yellow mouth; maybe it's a cowbird if it has a deep pink or reddish mouth.

Good birding, Larry H. Joplin MO.

From: Bet Zimmerman [mailto:ezdz"at"charter.net]
Sent: Thursday, July 21, 2005 9:48 PM
Subject: Info on cowbirds

I put up a webpage with some interesting info on cowbirds at http://www.sialis.org/cowbirds.htm. They really are fascinating birds. I read they could lay an egg in 4 seconds!

Thanks to Lara Hampton, Keith Kridler and Elizabeth Young for letting me use their photos. (I’ve never had an egg in my boxes.) I’ve summarized info from the Bluebird_L archives. Seems like Keith gets the most cowbird action. Keith, am I correct in saying that Cowbird’s eyes open on Day 2, and also that all the Carolina wrens in the nest in the photo eventually died?

If I’ve messed anything up, or you have more interesting factoids I could include, please let me know!

Bet from CT

From: bookfanaticef-bluebird"at"yahoo.com [mailto:bookfanaticef-bluebird"at"yahoo.com]
Sent: Friday, July 22, 2005 2:05 PM
Subject: Re: Info on cowbirds

Looks like a great "factoid" page! The pictures are great. Something that may interest you, and others on this list--or something to ponder, anyway. UNfortunately, I don't have any specific sources, so you may want to corfirm this, but....

Cowbirds are a species whose song, calls, and behavior, etc is genetically-encoded (or mostly so), as well as their recognition of their own species. Being raised by a species not their own (usually not even a closely-related species), it would be more logical to assume they'd hang around their foster parents species--but Nature has counteracted this to fit in with their unique breeding strategy. Therefore, a cowbird innately knows its own song and calls, its own displays, and recognizes its own species (which it joins up with in flocks sometime after becoming independent), despite having never encountered another of its own kind before.

This is the case in some other birds as well, but I believe many other species having such things "built-in" are raised by their own parents, and so have this encoding reinforced by learning at least for some things, although some birds (like cowbirds) simply "know" things, like where to migrate, and some solitary species don't even have others of their own species to follow (pretty amazing!). I think (though don't quote me on this, as I don't have any reference books with me as I write this), as a general rule, species having "innate" songs also have relatively simple songs, whereas birds with more complex songs have to learn them, or at least partially learn them, from others of their own species. Can you imagine, for instance, simply being able to speak English fluently the first time you met someone who spoke English if all you ever heard up to that point in your life was Japanese?

Other birds learn their songs, etc., and experiments show that nestlings raised by parents of another species become confused, and learn the wrong song (or a garbled mush of what parts of their songs are encoded mingled with their foster parents songs), and when mature, will try to pair up with their foster parents' species, not recognizing their own species (think ducklings imprinting on people, etc).

Despite the fact that cowbirds present a problem to many other species that they parasitize, I find them quite fascinating.
ELizabeth F
Gainesville, FL

Keith Kridler Mt. Pleasant, Texas
We are not supposed to send pictures to the list but since this good one showed up we can learn from it. You can clearly see the color of the insides of the mouths of the baby bluebirds and I would describe them as more yellow than orange. At 6 days the baby bluebirds are just opening their eyes and probably don't have good vision yet. At this age they basically just reach up high and open their mouth and hope mom or dad puts food well down their throat to trigger the swallowing instinct. They can react to a shadowy movement now and moving your finger above them triggers the feeding response especially if you whistle at this time. The bird on the top left will get the food this trip! If the entrance hole is too big and a predator can reach in the baby bird on the left will get pulled out of the nest and become food for another species!

Cowbirds would have had their eyes open a slit for 4 days or so by this age and they will actively seek out the foster parent when they enter the nestbox or simply position themselves to be under the entrance hole and receive the most food. The baby cowbirds have a dark orange or red mouth lining which really stands out in a group of yellow open mouths. If there is a shortage of food in any species of bird nest then the runts normally starve to death first since they cannot get enough food to maintain body growth. Starvation even for a few days will create weak bone, muscle and feather growth. Remember that these baby birds will have to be able to recognize and avoid predators in as little as 10 more days when they fledge!
One day in a baby bluebirds life while in the nest is like a full year in a baby human life. Imagine having a poor diet for a whole year of life for a human under the age of 6 years old!

Life for these birds is a continuous race against time! They must remain in top physical condition as the ones who lose any of their senses are more apt to become predator food. Just like the bike racers in France who get eliminated from the race when they fall too far behind due to fatigue, accidents, illness or equipment failure, in a birds life they would be terminated by an unfriendly environment. Even though all of the men in the bike race are in top condition compared to the rest of the human population they only have a few years where they can compete at this level. That is why small songbirds can live for 20 years or more in a cage but only a few will live beyond 5 years old in natural habitat where the weak or the slow or the ones simply careless for just an instant are eliminated. KK

Keith Kridler Mt. Pleasant, Texas
Last week I saw a huge flock of black birds feeding at a cattle operation. I drove on back to where they fed the cattle and was surprised that about 95% of the birds were all Brown Headed Cowbirds. Normally they are a mix of about 7 different species of birds but I really only saw Starlings and Cowbirds and there were easily 10,000 birds maybe twice that many.

A couple years ago in NABS quarterly publication the Bluebird there is an article on research into cowbirds parasitizing nestboxes where the guy installed about 1,200 nestboxes for Prothonotary Warblers but for some reason used a 1&3/4" diameter entrance hole. Over the course of 10 years the bluebirds using these nestboxes lost more and more of their nests to cowbirds and other predators, mostly raccoons.

Cowbirds prefer fragmented forest edges as do snakes and most other four legged predators. Bluebirds are a species that will nest in open park like areas with scattered trees. They will also nest in power line right of ways carved through dense forest if there is short grass in the right of way.
They prefer to nest were the grass is maintained in a short or sparse state by grazing or occasional mowing. Forest fires or grass fires create excellent habitat for bluebirds for at least one season. Bluebirds do well in areas where new pines are planted if nestboxes are added as the trees normally take 4>5 years to fill in and kill out the grasses and insects the blues rely on.

Look around your area now and find a park or cemetery or possibly even industrial land that has enough grass for bluebirds to nest. Once you get bluebirds nesting it is easier to find someone to check these nestboxes and you can go start another small group of nestboxes in another area. KK

I would also be very interested in the notes on Cowbirds.

We've had a pair hanging around for a few weeks and I'm worried about them
leaving eggs in the natural nests of the Tufted Titmice and Chickadees. I
have no idea where their nests are, to check for cowbird eggs and remove
them.

So far, they don't go near the BB house, which is about 60-70 feet away from
the feeder, and 70-80 feet away from our house.

Donna

Hi Donna,

The cowbird presentation was geared toward Black-capped Vireos and Golden-cheeked Warblers; Bluebirds weren't really part of the discussion.

Both the Tufted-titmouse and all Chickadees are cavity nesters and Brown-headed Cowbirds occasionally but rarely parasiticize cavity nests.

I've trapped and placed cowbirds in a box with a 1.5" entrance and they were able to work their way out, but with great difficulty. In my research with traps designed by Texas Parks and Wildlife, they would never voluntarily enter a 1.5" 'slot but readily entered a 1.75" slot.

Somewhere in the archives there is a post about a cowbird egg in a bluebird nest box, but I would guess it's a rare occurrence and that a baby cowbird might not even be able to get out of a typical bluebird nest box.

Thanks,
Rob Barron

From: Pauline Tom [mailto:ptom"at"austin.rr.com]
Sent: Wednesday, May 03, 2006 7:30 AM
Subject: cowbird eggs in bluebird nestbox

I photographed a cowbird nestling in a Bewick's Wren nest several years ago inside a 4" PVC nestbox with 1 1/2-inch hole (not enlarged).

Pauline Tom
Mountain City (no mountains) TX

Keith Kridler Mt. Pleasant, Texas
Cowbirds are smaller body wise than a Starling. Back in the 1970's I was finding Brown Headed Cowbird eggs in my nestboxes that I drilled with a 1&1/2" Spade or Paddle bit. Not always precise as they tear the wood. Dr.
Zeleny assured me that these cowbirds could NOT enter a 1&1/2" perfectly drilled entrance hole. He had been bluebirding for almost 60 years by then, fledged thousands of native birds and it just did NOT and WOULD not happen.

In the 1980's Dr. Zeleny was checking his nestboxes and WOW he found three cowbird eggs in three different nestboxes along one section of his bluebird trail!!!! At least ONE female cowbird was laying eggs in his boxes.

Now Cornell says that there is a chance that some female cowbirds actually will back up to the entrance hole and "squirt" an egg into the nestbox without entering the box. OK that might be possible. BUT like Pauline I have found Cowbird eggs in PVC nestboxes that are drilled to 1&1/2" but these are only 1/4" thick walled and thinner walled nestboxes allow larger birds to enter easier. It would be almost impossible for a cowbird to hold onto the edge of a PVC nestbox entrance hole and also get their butt in a position to put the egg inside the box.

BUT I also used a LOT of nestboxes where I glued Formica on the nestbox fronts to see if House Sparrows would use a slick fronted nestbox and with these the entrance holes were drilled with a 1&1/2" Forstner bit. Perfectly round and the Formica protected the nestbox front from enlargement and Cowbirds were still laying eggs in some of these. AND on occasion I actually found where the cowbirds had removed a bluebird egg from a deep nest so SOME of them were actually small enough to enter the box to remove an egg.

When you walk up to your nestbox the first thing you should look to see is if there is an egg directly below the entrance hole. I have found dozens of eggs over the years that appear to have been dropped by a cowbird either as she was squeezing into one of my nestboxes or as Cornell thinks might happen, that the female was attempting to lay an egg through the hole from the outside.

Peterson oval holes and the Gilwood mouse hole and slot boxes will make it easier for cowbirds to enter your nestboxes as all of these are large enough for Cowbirds to easily enter. I got a call yesterday from Don Hutchings and he found Cowbird eggs this week in his new wood nestboxes with 1&9/16"
entrance holes. Don also found a Dwarf bluebird egg about the size of a large English Pea this week.

I have good photo's of cowbirds that laid in a Carolina Wren in a Gilwood box that I showed at NABS 2006 and also a shot of Great Crested Flycatchers from last year that had five eggs and a cow bird egg in their nest. They used a 1&3/4" entrance hole. The fly catchers are checking out huge purple martin gourds that I have hanging all around the yard this year. Tufted Titmice fledged from an 11" diameter gourd hanging about 14 feet off the ground in a tree.

Off to go build 45 nestboxes for Gifted and Talented K>1st. graders at the city park. I hope we don't need any band aides.....KK

Hi Pauline,
Very interesting. I'm sure that they do occasionally parasitize cavity nesters but usually they choose an easier location ton dump their egg in.

The speaker you got for the NABS meeting from the Nature Conservancy was excellent. He stated that the Federal depredation order against Brown-headed Cowbirds made it legal to "dispose" of adults, eggs, and nestlings, although technically only adult females were covered.

I'm not sure he is correct that every state sees it that way. I did a research project on them in college and in NY at least we had to have a permit to trap them.

In any case, his point was that most species aren't negatively affected by them enough to be a major prolem. In my opinion, any bird capable of laying 40-70 eggs in other birds nests is potentially a huge problem. One thing he didn't mention is that Brown-headed cowbirds have a very short incubation period, so their eggs usually hatch first and their babies often kick the other eggs out before they hatch. As good Bluebird monitors, we should remove any egg or hatchling from our nest boxes that we are sure is not a Bluebird.

Thanks again for a great conference.

I've always found it fascinating that cowbirds would lay in a nestbox (or natural cavity for that matter), particularly when they need to lay the egg through the entrance hole. I would think that if the egg hit one of the host's eggs there would be a risk of eggs breaking, which would be detrimental to both the cowbird and the host.

Mike Donahue
Seattle

Hi group,

I wrote this earlier:

As good Bluebird monitors, we should remove any egg or
hatchling from our nest boxes that we are sure is not a Bluebird.

I want to thank Pauline Tom for pointing out to me that my words sound like I'm advocating removing other cavity nesters from Bluebird nest boxes. What I meant was that if you are sure an egg or chick in an existing Bluebird nest is not a Bluebird egg or hatchling. it is ok to remove it. I'm not advocating removing other native cavity nesters from unoccupied Bluebird nest boxes.

Thanks Pauline. Between you and Bet, MJ and Linda, I'm supervised pretty well! I love it!

Thanks,
Rob Barron

From: "Evelyn Cooper: Rob, I don't quite understand your first sentence in the above quote. It sounds like these statements contradict themselves. Could you explain it? The only time you can legally remove native cavity nesters' nest, eggs or possibly dead chicks is when that nesting cycle is over. Evelyn

Hi Evelyn,

I think we need Jimmy Dodson's help here! I'm learning a lot from
the knowledgeable people here. To make it simple, what I was trying to say was that if you are sure you can ID a cowbird egg or fledgling in an established Bluebird nest, it is OK to remove it. Cowbirds aren't native cavity nesters. Does that make sense?

Thanks,
Rob Barron

Cowbirds aren't native cavity nesters... they really aren't classified as any sort of nester... technically they are "brood parasites" -- they go around laying their eggs in pretty much any "songbird" nest they can find from cavity nesters to warblers to wrens, etc. They cover the spectrum.

Historically, reports for observations were centered around the midwest.
Cowbirds likely expanded their range b/c of human caused changes in habitat, but that's really just an hunch... there's no evidence that really substantiates it. In the Midwest, cowbirds "parasitize" nests along forest edges. Unlike the midwest, a number of fairly recent studies in eastern forests show that cowbirds do not effect edge nests as much as forest interior nests. But there again, they are opportunistic. My hunch is that they adapt their behavior fairly readily over a short period of time... I pretty much observe them in every habitat although their abundance does vary.

That being said, cowbirds are actually covered under the Migratory Bird Treaty Act because they are native to NAmerica and are not a "gamebird".
So, if you find a cowbird egg in an active nest, just like with the other eggs, you are not legally allowed to remove it. I've asked a few folks in recent years and even though I nor they like cowbirds b/c of the "threat"
and "harm" they pose to residents and migrants, we have to live with them.
They are just "making a living too" as much as I (and others) may dislike it.

We sent this link out about two weeks ago, but in case you missed it... it's the link to the US FWS Division of Migratory Bird Mgmt which lists those species that ARE NOT covered under MBTA. The link is:
http://www.fws.gov/migratorybirds/issues/nonnative/MBTA-Protected&NonprotectedSpecies.htm

Hope this helps clear some questions up. Let me know if there are others.

--J

Hi Jimmy,

Of course you are right -- Cowbirds are protected legally under the MBTA.

But as we know, the USFWS has approved the removal of Cowbirds as well as the trapping and killing of these birds in areas where they endanger song bird survival (e.g., Kirtland's warblers).

Clearly an individual bluebirder does not have the written legal authority to remove a cowbird egg or hatchling. But if the Cowbird is not removed the chances of fledging Bluebirds from that box are probably slim. We are out there to raise Bluebirds not Cowbirds.

This is one of those imponderables in my opinion. It is not a perfect world and laws cannot cover all situations. On occasion I make decisions that might slightly miss the stated law but capture the spirit of the law (as I see it).

So my unofficial advice is to think about how you want to handle this -- do as you think prudent -- and then keep your decision to yourself.

Just to be crystal clear -- such "reasoning" would most definitely NOT apply to a nest of House wrens however as there are no Bluebirds to "save" in such a situation.

Bernie Daniel

Keith Kridler Mt. Pleasant Texas
When in doubt check with your local wildlife officers in your area and talk with the ones who will be enforcing these laws. See how they interpret the depredation section of the migratory bird act. Ask how they interpret the section that mentions "about to begin depredation" of your property or crops.....Bluebirds are a crop on your trail are they not:-))

Also sometimes it is better not to broadcast methods used at all times on your trail.

For the next week everytime you look down at your speedometer and see that you are breaking the speed limit/law; go ahead and report this to the Highway Patrol and send them a check to pay for your local speeding fine. In other words try to go through life without bending ANY rules/laws or heaven forbid breaking any of them. KK

Hi KK and all,

Cowbirds can -- and do -- lay eggs in wooden nest boxes with a 1 1/2" hole with guard. I don't know at what point the egg was laid, but I saw a female cowbird enter and exit one of my boxes.
It was a tight fit, but she made it. I checked later and found one cowbird egg among bluebird eggs that were already in the box.

MJ
Mary Jane Shearer; Tucker, GA

From: Tnbluebirdman"at"aol.com [mailto:Tnbluebirdman"at"aol.com]
Sent: Tuesday, May 23, 2006 9:38 PM
Subject: What Would You Do??? Please Vote!!!

Hello List,
Last week, I watched with great anticipation as a Male Carolina Wren began excavating 1 of the flower pots hanging on my front porch. He worked in Ernest for a few days putting in nesting material he hoped would suit his potential mate. His work finished, he didn't wait long as a female arrived on the scene and began her inspection. It suited her just fine and her job now began. As I went for the Sunday paper, I noticed a female cowbird pacing nervously on my porch railing. What happened next is well known among the birding circles. Tonight, I took down the basket to find 5 little speckled eggs and 1 large speckled egg. I thought for about 2 seconds and went to get some tongs and carefully removed the cowbird egg. The female Wren came back shortly there after and began to sit on the eggs again totally unaware that the predator egg had been removed. I realized that I tampered with Nature but I KNOW That this type thing is a strong contributing factor to the decline of our native songbirds...

Bob in NE Tn. PS, Thanks ROB for the modified Petersen House. My Blues loved it and a brood has already fledged!!

Hi Bob,

Thanks for giving me an opportunity to vent.That's a dilemma we all must face individually and probably shouldn't go public with. Carolina Wrens are listed as "threatened" in PA, but I don't think they are in TN. I don't think Eastern Bluebirds are listed as threatened or endangered anywhere.

Personally, I find Brown-headed cowbirds about as appealing as a tape worm. There is something fascinating about brood parasites from an evolutionary biology standpoint, but the real issue is how man changed the habitat and made it possible for them to stay in one area all during the nesting season, thus impacting songbirds more than they would have when they followed the buffalo herds.

Keith Kridler mentioned buffaloes being hunted for their leather which made good industrial belts. Just as much evidence exists that they were hunted almost to extinction to remove the primary food source of the plains Indians and thus pacify them. In 1874, the Secretary of the Interior Delano stated, "The buffalo are disappearing rapidly, but not faster than I desire. I regard the destruction of such game as Indians subsist upon as facilitating the policy of the government, of destroying their hunting habits, coercing them on reservations, and compelling them to begin to adopt the habits of civilization."
Two years later, reporter John F. Finerty wrote that the government's Indian allies "killed the animals in sheer wantonness, and when reproached by the officers said: 'better kill buffalo than have him feed the Sioux.'" Sheridan added that "if I could learn that every buffalo in the the northern herd were killed I would be glad." We reduced the Bison population from 30 million to one thousand in less than a century.

Keith Kridler mentioned screaming. When we find a Brown-headed Cowbird egg in one of our songbird nest boxes, we all want to scream.
However, each and every one of us bears some responsibility as a member the human race. We all want bigger houses, more land, watered lawns, and the birds of our choice to look at. Birds and other animals do what they do without thought. It's what we greedily did without thought that we are now paying for. We've all tampered with nature so much that there unfortunately is no turning back. Cowbirds and House Sparrows are our fault. It's only when we take responsibility for our actions that we have a possibility of redeeming ourselves to nature.

Even in a place like Banf, Alberta, Canada, that appears to we humans as pristine, rugged Rocky mountains, humans have divided the land with highways, trapped or isolated Elk, Grizzly Bears, Wolves and Moose on either side, and introduced them all to the greatest predator of all in this humanly modified ecosystem, the automobile.

Aldo Leopold said "One of the penalties of an ecological education is living alone in a world of wounds." The more we learn and care about nature, the more aware we are of what we've done to her.

Rob Barron
Warrenton, Virginia (where buffalo used to roam)

Just this week i found a cowbird egg in a House Wren
nest. I've no idea how the female cowbird squeezed in
there & i've no idea how she expects the baby to
squeeze out.

This is the first BHCO egg i've found in a nestbox, &
i've been checking 100+ boxes since 1997. I'm weirdly fascinated...

Torrey Wenger
Kalamazoo Nature Center
Kalamazoo, MI

In a message dated 5/24/2006 10:46:50 A.M. Eastern Daylight Time, yumyumkatts"at"voyager.net writes:

Hello All......
I've heard of cowbirds depositing eggs in BB boxes. Never seen it, tho.

I do have some clear photos of cowbird eggs, one in a nest with three Chipping Sparrow eggs. Before the cowbird got there, there were four chipping sparrow eggs.

Anyone who'd like to see the photos, just drop a note and I'll gladly send them to you.

Bruce Macdonald, SW Ontario, south of Detroit

I have adopted Keith's suggestion about making a fake nest and putting it in
a tree to trick Cowbirds into laying their eggs in it.

I have decided that since the Cowbirds do not "pay rent" (build a nest,
incubate or feed their babies) that any time I find a Cowbird egg in a nest
on my property I will put their eggs in the fake nest.

They have the option of caring for it, or not.

Donna in Virginia

Hi Donna,

That's creative, but it still isn't legal during the time you "possess" the eggs between the parasiticized nest and the fake nest....

Bob, I'd be interested in hearing what the "offline consensus" was on the vote, as I'm guessing most people didn't vote in public :-) Can I inquire as to how many responses you got, and how many votes on either side?

Keith, I'm skeptical that a cowbird would use a fake nest. Have you seen them lay in one? They
sometimes flush birds to find active nests. I would think they might have evolved to recognize a
nest that is not in use. Also, they usually steal one egg and replace it with their own. Do they
ever lay the FIRST egg in a nest?

As far as I know, cowbirds will not build a nest and will not care for an egg in anyone's nest -
they never had, or have lost that instinct.

Bet from CT
More info on cowbirds and photos: http://www.sialis.org/cowbirds.htm

I have had a couple of cowbirds use a fake nest.

You either find an abandoned red bird nest or I had pretty good luck tying a strawberry basket in a holly bush and installing a good looking bluebird nest in the basket. Each night I would add a single House Sparrow egg to the nest until I got to about five eggs. I would wait a few days and begin all over again with one egg and add one each night to make it look like a female bird was laying eggs early in the morning.

What I found was that they would sometimes lay an egg and not remove one and sometimes they would remove an egg. The biggest problem I had was something was often eating all of my House Sparrow eggs in the nests and we had to constantly move nests. When you do something like this you see how often other bird nests fail.

I have actually seen that the first egg in a bluebird nest was a cowbird egg only it might have removed the blue egg when it laid it's egg in the nest.

This actually worked better when I was using about four "fake" nests and adding eggs in different areas of our yard and edges of the woods. Keith Kridler

From: wensuz"at"isp.com [mailto:wensuz"at"isp.com]
Sent: Monday, January 22, 2007 8:43 PM
Subject: cowbird interloper

Hi everyone, this is Wendy, in Wakeman, OH. For nearly a week now there has been a male Cowbird at my ground feeders. I shot my bb gun at it several times, in only flew off into the trees, but always returned. He is not a bully, and the other birds aren't particularly afraid of him, he actually seems quite benign. I have never had cowbirds interfere with my EABL or TRES nests, but they have been quite a problem for the Song Sparrows and Chipping Sparrows. That was at my old property, mind you, I don't know what they do here at my new property, for this will be my first nesting season here. I do remember seeing cowbird eggs in a BB nest in the Bluebird Monitor's Guide Book, so I am aware that they will parasitize the Blues too. Are Cowbirds protected by law? Are they even native? Has anyone had any problems with Cowbirds invading their BB boxes? I'm sure I am going to have more problems with HOSP than Cowbirds, but I was just curious because I have never encountered them before.