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Cowbirds in Nestboxes (Part 1)Date: Fri, 10 Mar 2000 06:43:11 EST JoAnn,Guilford,CT. Do Cowbirds bother BB 's? I know that they lay their brood in other birds nests and then off they go. there are at least 1 pair every year at my feeders, I do like their liquid sounding call but since I found out how they commit home invasions I scoot them away. Have a good day, I'm off to work Date: Fri, 10 Mar 2000 07:32:02 -0500 Jo Ann, There have been reported instances of cowbird eggs being found in nestboxes, but I personally have never seen it. It apparently is a learned behavior. I also have trouble envisioning a cowbird fitting through a 1 1/2" hole, but perhaps the holes in those particular nestboxes were larger. Brenda ... Date: Fri, 10 Mar 2000 06:45:38 -0600 A cowbird egg looks like a housesparrow egg. You can tell them apart if they are side by side since the background color of the cowbird egg is less green (more white). The problem is an earlier hatch date for the baby cowbird than the bluebird eggs. Merlin Wright at Brownville Nebraska ... Date: Fri, 10 Mar 2000 06:51:54 -0600 Mary Jane Shearer Hi Bluebirders! I'm another "newbie" so please excuse my errors. Have been enjoying all the birder news for a couple of weeks waiting for a subject that would incite me to write. [no pun intended!] COWBIRDS did it! We have 4 nest boxes-3 BB and 1 fancy one that has been ignored until this year when the chicadees chose to build in it. Last year we had our first cowbird experience. The female watched until both the bluebird and titmouse began laying eggs and quickly doposited one of her own in each of their nests. I removed the alien eggs but not before 2 BB eggs were damaged. I understand they either kill the BB chicks or starve them. I believe cowbirds deserve the same treatment as house sparrows. BB's haven't built yet, but they've checked out the house every day for about a week. A downy woodpecker spends the night in one of the boxes. Also have red headed, red bellied and pileated woodpeckers in the yard every day now. Time to go check on the birds. Date: Fri, 10 Mar 2000 11:32:03 EST Mary Jane Shearer Didn't mean to suggest killing cowbirds or any others. Don't think I could even kill a sparrow. Just don't think encouraging them around nest boxes is a good idea. Sorry I created such a firestorm with my first attempt. To answer your question, yes, they can get through a 1 1/2" entrance. Females are smaller than males, and I saw her coming out of the box. My boxes were purchased as "official" BB boxes and have metal guards, also bought as BB house guards. I measured them, and they are slightly less than 1 1/2" . As to whether I could identyfy a house sparrow, I believe I could. I refer to my Audobon Field Guide any time I have a question. Fortunately, house sparrows have not been a problem for me. Once again, I do NOT advocate killing any birds! mjs Date: Fri, 10 Mar 2000 10:10:24 -0800 Hi all; This Cowbird thread troubles me. Leaving aside for the moment the mechanics of how a BHCO might get into a BB box and our collective desire to see our little Blue bits of fluff succeed, I think we need to address the bigger question of why we feel the way we do about them. I get the distinct impression that some of our readers think that this bird is somehow a villain, scummy vermin, and an undesirable interloper. Something to be hated, reviled, despised, or killed on sight... Did I get that about right? For all of the consternation this bird generates; does anybody reading here know what it was called...say a 100 years or so ago? Lemme help you. In the recent past it was variously known as the, "Cow-pen Bird", "Cow Bunting", and a few other monikers too. But before that, it was known as the, "Buffalo Bird". How do you suppose it got that name? It got it because it's niche in life was to follow the herds of Buffalo roaming the country. This bird ate the insects attendant to or disturbed by the grazing and wandering of the vast herds of Buffalo. So, like most insectivores, it benefits us directly; and--sans our native Bison--continues to do so today; albeit with cows and other grazers. Of necessity, the Buffalo Bird had to move everyday to stay with its meal-ticket; the wandering Buffalo. It shouldn't be too hard to understand that when you follow a moving grazing herd, you can't sit still for a couple of months to build a fixed nest and raise a brood. So it evolved the capability to quickly dump an egg in a "local" nest, trusting the surrogate parent to raise and fledge the Buffalo Bird as its own young. Think about it! This bird demonstrates a marvelous adaptation for its itinerant lifestyle--yet some of you only seem to be able to find the time to despise it for that ability...! Getting back to our BB's, I'm not sure what the correct course of action is for you all. To me, as an insectivore, this bird is invaluable! As a parasitic nester, it's a royal pain to the other indigenous birds. To our BB trail work, it's death! I've not heard of any problems with BHCO to our BB's here in the San Jose, Ca., area. Other California birders may have had a different experience. Please feel free to chime in so that we can compare notes on problems with BHCO. Given that I don't seem to be bothered by them, my actual course of action is still in some doubt. Understand too, that this bird is NOT an intruder like our HOSP's or EUST's. It *IS* protected by the Federal Migratory Bird Act. I think I will do this: I usually try to keep track of birds nesting in our area. It's not too often that I don't know where an active nest can be found. If I find any BHCO eggs in any of the BB nests under my control, I will gather them, and move them to...oh, a HOSP or EUST nest (NOT in my nest boxes, of course) would be nice (:-)! On a further note: Anybody got a reading on what the fed's could, would, or might do to us if we removed a federally protected BHCO egg from our nest boxes? Feathered regards, Date: Fri, 10 Mar 2000 13:43:13 -0800 Jim....Thanks for another good post. You recommend an open mind and sometimes that can be helpful. Now that I have adjusted to your warm personality I have begun to appreciate your wisdom. (Take it easy on the Robin, will ya?) I agree I rather have a few blues than an apartment house filled with Starling. And variety is pleasing. However, while my open mind will allow Nature to own the Iowa bluebirds--not the case here in my life. Same situation with "my" land. Majority agree with you--all this stuff is rented from Nature and we are just passing thru for awhile. Not I Sir Walters! I owe my bluebird--whether he likes it or not! He belongs to me--he feeds my desire for ownership and when he dies, so goes a piece of me to return again when his son or daughter returns to check out the old place. So you keep renting yours Jim, but don't tell me how to feel 'bout what I own or who I am. Anyway I wondered where you had been and trust all is well with you and yours. I enjoy and learn from your posts and some times may take friendly exception. I don't revolve around my world, my world revolves around me. Your Humble Servant, Date: Fri, 10 Mar 2000 01:56:46 -0800 Hi Dusty, Although Santa Clara County has not had a significant problem with BHCO parasitism, the breeding population of migratory warblers was nearly wiped out by the BHOC in Monterey County. Volunteers were building special traps that would gas large groups of cowbirds that could be caught enmasse because they like to flock and feed together. Some of the migratory warblers simply will not distinguish between their young and the intruder. This whole matter of how much if any cowbird parasitism has done, however is a subject of great controversy, some of which is explored in the ABA magazine. It would seem, though, that man plays God sometimes, but never well.. Yours, Date: Fri, 10 Mar 2000 18:40:27 -0500 Vivian Pitzrick, Amity Lake, Belmont, NY about 90 miles SE of Buffalo. Several years ago I found one Brown-headed cowbird egg in a nest box with 5 chickadee eggs. The entrance hole was slightly larger than 1 1/2 in. Aren't cowbirds protected by law? Date: Fri, 10 Mar 2000 15:51:22 -0800 Hi Dave and all; Interesting. I guess that answers the question of whether or not we're permitted to interfere with that bird's way of life. I take it that these actions were made with the permission and blessings of the appropriate authorities. Yes? Anybody in that sort of position read this list? I'm quite certain that some more info along that line would be well appreciated... I don't want to give folks the impression that I'm in favor of BHCO bird proliferation. Quite the contrary. But, it's a native species that's been displaced a bit from it's former territory by the loss of the Bison's range. That's not really their fault. OTOH; I don't enjoy the fact that we're losing other songbirds due to the BHCO birds parasitic activities. The real issue is, that from time-to-time nature selects a species for extinction. Regretfully, in the more recent past, we (mankind) are too often the underlying cause of losses of this kind. But, unlike so many of the "do-gooder" activists, I don't for a moment consider us a disease or blight on the face of this planet. True, we can effect large changes, but that doesn't give us an implied right to pillage and plunder the environment. OTOH; species come, and species go. In the grand scale of things, we're certainly not the most successful eliminator of other species. Regretfully, given our current trends, this might change... I got lots of comments on my post. Thanks to you all. I was a bit surprised that no one commented on my idea of putting the BHCO bird eggs into House Sparrow or Starling nests...(:-)! Dusty ... Date: Fri, 10 Mar 2000 21:27:34 -0500 Dear Dusty, Your initial post about Brown Headed Cow Birds was a plea for tolerance of this species, and, I applaud you for bringing this to our attention. And, placing Cowbirds eggs in House Sparrow nests is very creative, if the sparrow's eggs are removed first. However, I believe I am more disappointed with our own species thoughtlessness and the impact that this mindset creates on other species of this planet than you seem to be. We may not be a blight, but we seem to be doing a lot to earn that title. You said "species come and species go". Given time to research the topic, I'm sure I could list hundreds of species that we have caused to "go" in the last hundred years. And, I'll top my list with the once, most magnificent of all native cavity nesting birds, the Ivory Billed Woodpecker, despite continuing unsubstantiated claims of sightings. But I can't think of a single true species that has "come" in all of recorded history. Can you? Gary Springer ... Date: Fri, 10 Mar 2000 21:51:38 -0600 I got lots of comments on my post. Thanks to you all. I was a bit I am sorry, I missed that! Probably best idea of the century. I wonder how they'd react, though. Robins, among a few others, will dump the BHCO eggs out of the nest pronto! Bill Darnell, Savannah, TN Date: Sat, 11 Mar 2000 08:53:47 EDT Rhonda Watts Thanks for the response on the bronze-headed cowbirds-- definitely not the same situation as with house sparrows. At least they aren't pecking heads in. Here's a little more info on BHCO. It was mentioned that robins will throw out BHCO eggs; there's another species (I've only had one cup of coffee this A.M., can't remember off the top of my head which, but someone will know) which builds another nest or more right on top of the first nest containing BHCO eggs. The species with this ability to "fight back" against the BHCO are those which live in open, brushy, or forest edge habitat areas the BHCO always did use. Those which use deep forest have never developed the instinct to recognise or deal with the problem. With forest tracts getting cut up into smaller and smaller sections with open area in between, it's now easier for the BHCO to get to their nests. Apparently the BHCO also is developing the tendency to go further into wooded areas, as well. Funny, isn't it-- how fast BHCO learn the new behaviour! Date: Sat, 11 Mar 2000 10:22:14 -0500 Rhonda, I think that the bird that you're thinking about is the yellow warbler. But, I rechecked my field guide to be sure and read that the warbler responds by burying the eggs under a new nest lining. Nests have been found which have up to six layers, each containing one or more cowbird eggs. Patty in WV ... Date: Sat, 11 Mar 2000 17:56:20 -0600 ... Also, isn't there a warbler which the cowbird is being credited with driving to the brink of extinction? I have read about, and want to say Kirtland's, but don't know my warblers well enough. Bill Darnell, Savannah, TN Date: Sat, 11 Mar 2000 16:14:22 -0800 (PST) Yes Bill and everyone, It is the Kirtland Warbler that the Cowbird is destroying. I have done alot of reading on this subject. Here is something brief. The Kirt Warbler requires highly specialized nesting habitat of dense YOUNG Jack Pine stands of 320 acres or more with trees 6-18 feet high. That is not all, these trees need intense heat from forest fires to release seeds from their cones. To help them....people are LEGALLY burning of trees that is controlled and logging mature trees and replanting several MILLION seedlings each year; habitat protection; and continual TRAPPING and REMOVAL of the Brown-headed Cowbird, a severe nest parasite. So that is just a brief description. Slowly.......they are coming back.......slowly. kevin bloom of Sunbury Pa... Date: Sun, 12 Mar 2000 13:01:16 -0600 Keith Kridler Mt. Pleasant, Texas... Ice in the bird baths this morning! Cowbirds do lay eggs in boxes with entrance holes as small as 1&7/16" in East Texas. When walking up to a nestbox always look right below the entrance of the nestbox and sometimes you will find a cowbird egg right on the ground. I believe the tight squeeze will sometimes "pop" an egg out of the female as she enters the tight entrance. Sometimes the cowbird will remove a bluebird egg and sometimes she will just add to the number. On three occasions I have watched the cowbirds remove bluebird eggs and recovered two of the eggs. One was from a natural cavity in a snag in a lake and the bluebird egg was dropped in the water and sank before I could paddle over to retrieve it, the other two were dropped within fifteen feet of the box.The cowbird when she removes the egg will leave two marks in the egg less than 1/2" apart. Cowbird eggs hatch in 9 days so a cowbird can add eggs to a nest that is already being incubated and still have their eggs hatch first. Bluebirds are programmed to have all of the young hatch at once. At one box with 4 BB eggs a cowbird added two eggs. 1 cowbird hatched on Monday, the second hatched on Tuesday. The first BB hatched on Wednesday and was now 1/3 the size of the first cowbird. Since the female bluebird had quit incubating and begun feeding, the second and last BB egg to hatch came on Thursday and the now "huge" 1st cowbird was getting most of the food. Friday the second cowbird died (starvation?) and the bluebirds were terribly small. Monday a black rat snake had gotten past the Krueger snake trap and ate the young and was trapped on the way back down the post. Cowbirds are such a rare occurrence in nestboxes that you might want to just watch the progress. Cowbirds have white fuzz where the normal BB will have black or dark fuzz when they first hatch. For those removing sparrow eggs this year try your hand at nestbuilding in trees and bushes. Mark the house sparrow eggs and place them in your "manmade" bird nests and monitor them daily to see if cowbirds will lay eggs in these "fake" nests. It is supposed to be better if you just add one egg a day till four or five and wait a week remove all eggs and start over. This simulates an "active" nest available for this parasite bird. These "dumped" cowbird eggs could then be added to the House Sparrow and Starling nests for your "observations". This nestbuilding will make you appreciate the ability of your birds to be able to keep a nest in a tree! I have found that attaching a strawberry basket to a tree limb and building a nest in this is acceptable to fooling cowbirds. You will also learn that every predator will soon learn where these nests are and begin raiding these unguarded nest! It is amazing to me that any nests are successful! Although illegal for us to bother the cowbirds, our local "Wildlife Control Officer" has been transferred to central Texas for 6 months to work at eradicating the Brown Headed cowbirds to allow the Kirkland (? or other) warblers to nest. Texas is going to spend a great deal of $ to have dozens of trappers and biologists working on this three year project. As usual what is illegal for us to do, the government will pour the money on to "research" this project. KK Date: Sun, 12 Mar 2000 18:37:37 -0500 Keith, I believe the warbler that is "in trouble" in Texas is the Golden-cheeked Warbler. Brenda ... Date: Fri, 31 Mar 2000 07:28:08 -0600 Keith Kridler Cool 50* in the beautiful Tri-lakes region of Northeast Texas (Mt. Pleasant) 2 eggs: It could be that your bluebird is laying eggs in the afternoon and not morning hours. You might also have had another female dump an egg in this box if she was driven from another nest site while in the process of laying eggs. Cowbirds: I read somewhere that a female cowbird had laid 35 eggs over a 6 week period in one bit of research. A yellow shafted flicker was recorded as laying 29 eggs in 31 days. As the flicker laid the second egg the first was removed thus leaving her with only one egg each day. In attempting to complete a full clutch of eggs her egg laying cycle was not shut down. Seems some (or maybe most) birds can control clutch size to a degree. Makes you wonder why some Eastern bluebirds lay 3 or 4 normally up to a high of 6 and others like the Mountain bluebirds will lay upwards of 10 per clutch. If we are having so many millions of man-hours of observations about bluebirds in nestboxes & yards where we can watch ever movement 365 days a year and still have so many questions, how will we ever learn about the habits of secretive/rare species? Mealworms: For those with truly unlimited mealworm feeding in their yard it might be interesting to observe if you have larger egg clutches from the birds feeding compared to those in the "wild". How are hatching rates compared to "wild" and average number of eggs/nesting attempts. What about the time between nesting attempts? Backyard research is sometimes better than a single bit of research done by people just interested in numbers. KK Date: Sat, 13 May 2000 22:37:38 -0500 Keith Kridler Mt. Pleasant, Texas 85*F today heading down to a chilly 53*F tonight :-) cowbird egg: I found one today in an old 4" PVC box dating back to early 1980's. I shipped off the old bluebird nest from it ten days ago and now there is a new nest and five bluebird eggs and one cowbird egg. The entrance hole should be 1&1/2" on my old boxes but will accurately measure it later this week. The problem with leaving this cowbird egg is that it should hatch in 9 days after incubation starts. (To big of a head start on the baby bluebirds.) I have saved a House Sparrow nest with five eggs also laid within these ten days and will move the Cowbird egg or eggs in about 4 days. I just got a digital camera with macro capability and will find a site to post these Cowbird pictures to if and when they (it) hatches to hopefully show the size increase over the parasitized bird young. flying squirrels:I have had flying squirrels (24) all spring in a box just
across a narrow county road from an active bluebird nestbox. (1st nest fledged
and 2nd nesting just about to hatch out) Tonight while my son Shawn checked the
squirrels (we check them once a month) I checked the bluebirds, well Shawn
"accidentally" scared one squirrel out of the box and the bluebirds went
ballistic! Both bluebirds began attacking that poor squirrel as it ran up and
down and round and round the power pole. The male was hot on it's tail as the
squirrel jumped off the very top of the pole. It did a steep power dive just
inches from the pole and went almost to the ground before flaring out and
heading to a nearby tree. The male BB lost the squirrel on the sharp flare but
did a wing over and raced after the squirrel right into the tree branches where
it eventually lost the rodent! The bluebirds chatter was intense and their bill
clicking must have sounded like machine guns rat-a-tatting just inches away from
that flat tailed squirrel! I have never seen bluebirds that aggressive, they
totally ignored Shawn as Date: Thu, 18 May 2000 17:49:16 -0700 A question: My Stokes guide warns that Cowbirds may lay eggs in a Blue's nest. I keep a close eye on my Blues' box, and mama has 5 eggs now, to hatch this week. There are Cowbirds around here, but they seem too big to lay an egg in the box. Do they lay is outside & carry it in? Do they manage to get that big behind into the box? Just wondering.... Nicholas Date: Thu, 18 May 2000 22:18:24 -0500 Nickolas asked how cowbird eggs get into a bluebird box. In this area the female cowbird is much smaller than the male and she is able (occasionally) to get through a 1 and 1/2" hole. Bluebird Bob, Northeast Oklahoma. Date: Fri, 19 May 2000 08:09:57 -0700 Bob & all: I have received about a dozen replies. All except for 2 say that the Cowbird will only lay in natural cavities. One writer witnessed a Cowbird come out of a box with 1 1/2 hole. The writer, as Bob, also indicated the female is much smaller than the male. So there must be a variance in size of the Cowbirds? Thanks again to everyone for your responses. Nicholas ... Date: Thu, 25 May 2000 07:25:21 -0500 Keith Kridler Mt. Pleasant, Texas a muggy 78*F at 7 AM Texas is in the second year of a massive cowbird trapping operation along with the USFWS. This is mostly going on in the central part of the state. I have not been able to get any information about how many cowbirds (Brown-headed) they are removing (6 month trapping season) but it is mostly to save our warbler population. I am not seeing very many in Northeast Texas this year although I do have an egg in a 4" white PVC nestbox wired in the midspan section of a barbed wire fence. I have found that boxes mounted at least 2 feet from a fence post hanging only on wire are not bothered by fire ants. (I lost 3 House Sparrow nests to fire ants last week alone!) This is the first time I remember ever finding a cowbird egg in a PVC nestbox. There is a wood nestbox just about 200' away with a new Eastern Bluebird nest started and I will watch it as in the past I have found 24 (normally one egg per nest in three or four nearby boxes) cowbird eggs in boxes along about a 1 mile stretch as I guessed that the female cowbird stakes out about 600 acres to lay eggs in. The first time I checked this box the cowbird egg was partially buried under the 5 bluebird eggs. Yesterday the cowbird egg was on top of the pile and one bluebird egg was partially buried in the nest cup so she is rotating the eggs. In this heat none of the eggs will get chilled! I plan on removing the egg as soon as it hatches and bring it to a nest near my house to monitor more closely as it is now about 10 miles away. In the past I have located old nests in shrubs and fence lines and reworked them and used House Sparrow eggs to simulate an active bird nest. By marking the sparrow eggs and adding one egg a day you can tell when a cowbird dumps an egg in your fake nest. This also was a good way of monitoring the number of nests that are raided by other predators as often the eggs will disappear altogether. I remove the cowbird eggs from open nesters when I find them in red bird and Mockingbird nests ETC. Only the cowbird survives in these open nests. KK Date: Thu, 25 May 2000 19:53:48 -0500 How interesting that Keith should post about cowbirds. I found my first cowbird egg in an active eastern bluebird nest a couple days ago. I removed it and left the four bluebird eggs, but today on checking, I wasn't certain if the eggs were warm. (When it's in the 90s outside, it's hard to tell whether the egg is warmer than ambient temp!) Keith, or anyone, would a cowbird egg in the nest cause bluebirds to abandon the nest? On a different topic, on the way to check that nestbox, I walked through my hay meadow, where the hay had just been rolled today. As I approached the gate, I saw a turkey vulture sitting on one of the new rolls of hay, and another sitting on the ground. When I came around the bend, there were a total of 12 vultures in all, just sitting on the ground, on rolls of hay or in a nearby dead tree. I didn't see anything they could be eating, so I found the sight interesting, to say the least, since I have never seen them at this particular location before, and certainly not that many at one time! Kate Oschwald Date: Tue, 30 May 2000 06:27:21 -0500 Keith Kridler Mt. Pleasant, Texas I also found a Red Bird nest with two of their eggs and one Brown-headed Cowbird egg yesterday. I will move this to a house Sparrow nest and see if House Sparrows lose young when the cowbird egg hatches early. KK Date: Sun, 4 Jun 2000 14:51:55 -0500 Keith Kridler Mt. Pleasant, Texas 120 miles East of Dallas on I-30 & 65 Thanks Walt on adding to the information! I was not being critical of this nestbox situation just wanting others to be observant. The nest cams this year are showing that many of our cavity nesters can perish in just minutes right before our eyes. The Minnesota groups records from the 80's to early 90's showed that of eggs hatched between 2533% of the young birds would die before fledging state wide from all causes. Cowbird: Remember I moved the cowbird baby from a PVC box with baby bluebirds several days behind in growth to a box of 4 bluebirds the same age and size to see how the competition for food would be? Well the Eastern bluebirds removed the cowbird baby from the nest ending that experiment in a hurry. I foster parented 5 orphaned Eastern Bluebirds into a nest containing only
one young 9 days ago and all 6 are ready to fledge. Adult birds are very Subj: [Bluebird] Cowbirds Revisited
Subj: [Bluebird] Cowbirds Revisited Date: 10/13/00 6:34:28 AM Central Daylight Time From: Edandmj30084"at"aol.com Hi Keith, Do you think this means that these birds can count? Serious question. MJ Many have reported finding Brown headed cowbird eggs in nests over the years and I found two bluebird eggs that were removed out of a nest of four eggs and the cowbird laid two more of her eggs in the nests in two days.
Subj: [Bluebird] Cowbirds Revisited Date: 10/13/00 7:10:28 AM Central Daylight Time From: jabbest"at"americu.net (Brenda Best) MJ, I don't think they can count, but "somehow" cowbirds learned that their eggs would be rejected if they didn't remove the host's eggs. Here's what The Birder's Handbook has to say about clutch sizes: Some birds, such as Barn Swallows, doves, shorebirds, Tricolored Blackbirds, large raptors, and many small songbirds, lay a precise number of eggs in each clutch. Removing one or more eggs, adding additional ones, or the hatching of some, will not lead the female to deviate from the predetermined number. Other birds, however, respond to the loss of eggs by laying more. The domestic hen is the best-known example; take away each egg she lays, and she can lay at a rate of very nearly an egg a day for a year (a talent which, of course, has been enhanced through selective breeding). A Northern Flicker normally lays 6 or 7 eggs. When, however, all eggs after the first were removed from the nest of one female, she laid 71 eggs in 73 days. Such "indeterminate" layers, nonetheless, stop laying when they are sitting on the "proper" number and are left undisturbed. There is some sort of feedback from the number of eggs being incubated to the hormonal system that controls production of eggs by the ovary (only one ovary functions in the vast majority of birds). A clue to the mechanism has been provided by studies of Black-headed Gulls. Courtship in these birds stimulates the ovary to start producing eggs, and the female begins incubation with the first egg. The process of incubation starts to shut down the ovaries. One or two eggs may already be far enough along to complete their development and be laid, but not three. Therefore the female gull will lay a total of two or three eggs, but not four. If she is supplied with a wooden egg to incubate before the development of the first egg in her ovary has proceeded far enough, she will lay no eggs at all. Copyright =A9 1988 by Paul R. Ehrlich, David S. Dobkin, and Darryl Wheye. I think cowbirds are fascinating! How they developed the strategies that they did is a huge puzzle. Brenda
Date: Sun, 25 Feb 2001 20:08:34 -0600 In his response to my question of whether cowbird traps can be used for starlings, Tom Heintzelman of Milton FL asked: "Pauline, if an explanation for the "cowbird trap" you mention is available I would appreciate reading about it. Thanks." There's a photo of a cowbird trap and a success story at http://thecattlemanmagazine.com/issues/2-2000/coexistence.htm. Cowbirds are trapped in Texas because of their parasitism of endangered species' nests (golden cheeked warblers & black-capped vireo). The trap is walk-in size - something like 8' high X 12' length X 6' wide. "We had 212 cowbirds fly into a trap in 10 minutes" is a quote from one person participating in the program! IF these can be used to trap starlings in areas where starlings are more a problem than cowbirds, they would certainly trap a lot of starlings. Pauline Tom Date: Sun, 25 Feb 2001 21:33:12 -0500 Bill Darnell wrote: Also, I meant to mention on my last post, Cowbirds are protected, at least Yes, cowbirds are are a native species and as such are protected nationwide. I have read somewhere (I don't remember the details, unfortunately) that there are programs are in place in certain locations to reduce the cowbird population, but these are officially sanctioned and monitored. Otherwise, it is illegal for an individual to harm a cowbird, just as it is illegal to harm a house wren, like it or not. If you trap a cowbird, you must release it. -- Date: Mon, 26 Feb 2001 06:53:40 -0600 Keith Kridler Mt. Pleasant Texas Cowbirds being protected: There is a loophole in the federal regulations that basically states; a protected species maybe removed or killed IF it is about to commit predation on crops or other items of monetary value. It seems to me & the state of Texas that two species of birds rapidly becoming extinct would be more valuable than an exploding population of another species that just happens to be destroying 90% of the endangered birds nests with their own eggs. (I didn't check the final backyard bird count yet for Texas but the top two birds were House Sparrows followed by Starlings. I find this hard to believe since I was seeing hundreds of finches at the feeders at a time during this time period and no starlings and only about 6 house sparrows.) Check with your local game warden and get a written statement from him concerning House Sparrows, Starlings, Cowbirds ETC. before you begin trapping! Do you need X number of hours of schooling before you begin removal of these birds. Do you need a permit? This trap shown in Pauline's article is basically a modified version of Troyer's design and his is a reduced size exact copy of an Australian fish crow trap designed in the 1800's. This in turn was a copy of traps used to capture massive quantities of the "Kings" birds in England by the starving peasants. Remember the 4 & 20 blackbirds in a pie? They were trapped not shot. All three of these traps work on the birds dropping down through a narrow slot in the traps' roof and not being able to find the exit again. There is a black plastic dipped 1" hole sized chicken wire fencing available now instead of the Galvanized wire used in the past that is practically invisible at a distance. It will last about 15 years longer than normal chicken wire and is especially good for areas near salt water spray or in corrosive environments. This cowbird trap would work on starlings if the trap entrance were modified & especially if nestbox traps were used to capture the first starlings to add decoys to the cage and scrap human food instead of grain were used as bait. Did you notice that they only kill the female cowbirds and banded & released the males!!! Cowbirds work at hunting birds nests in a "pack" like wolves. There is one Alfa female and normally 4 but as many as 9 males hunting for bird nests. While the female is actively laying eggs all males in the "pack" will be mating with this female (unlike wolves) to increase odds of viable eggs. House Sparrows often engage in this type of multiple mating behavior also. KK Date: Mon, 26 Feb 2001 16:02:18 -0500 As I understand cowbirds, adult birds do not kill other adult birds. The adult female lays her eggs in other birds nests and the hatchling may kill the other baby birds of the host nest. Unless you have a permit, I believe it would not be legal to trap cowbirds. Perhaps checking with the local Fish and Wildlife Service would be a good idea to check the status of cowbird trapping. Alicia Craig From: Lonn and Linda [mailto:solong"at"teleport.com] Lonn in Roseburg, Oregon I was informed of the predator control available in Plow and Hearth www.plowhearth.com (early Spring2001 catalog on page 22) by my wife. It's a plastic tube extension for the entrance hole to protect Baby Bluebirds from jay and cat and rocky raccoon with the crow brothers, and as instructed by my penny-pitching wife: let's make our own! As instructed I mentioned the 100 ruined little clay decorative planting pots. The Main Man in her last club of cancer protectors used them with the idea to put wax in the pot to do some pretty inexcusable things. He always was a trouble to anyone; but that's what reorganization is for. We thought about how to use these, (my idea) and she mentioned some of the glass, ceramic cutting equipment we bought at the local vending machine they call Country Fairs, etc..., she was sure she'd use, (just no use for 3 years, Until now!) We used that saw blade, (cuts all metal , blah, blah, ) with the hacksaw and made the bottomless pot and used the ceramic drill bit to screw a hole into the lid overhang of the Nestbox. My experiment looks like a funkified nozzle with a eyeball that follows you around the room. I hope this works, if not it sure is a good laugh to look at. I'm going to do just one this year, as the two eyeballs may lead to the third eyeball and a pyramid scheme of housing for low-income tax preparers. P.S. I have terrible cowbird problems; (whether or not I'm sure of their killing my fellow bluebrothers?, am not), but I'd prefer an excuse to deviate them from my WEBL boxes. P.S.S. What's the trap Pauline Tom: bluebirds"at"austin.rr.com is availing too? Keith - Where will we find plans for a starling trap? Will a cowbird trap serve the purpose? I am in the process of taking up improperly placed boxes (50) on nearby agricultural use acreage. Approximately 10% of the boxes have woodpecker holes on the bottom side of the boxes. The entrance holes were sealed with a wood block during the winter (since house sparrows breed year-round here) so the woodpeckers found another way in. (I mention a cowbird trap because there's a cowbird trap already in place on the developer's acreage.) Date: Thu, 22 Mar 2001 13:54:24 -0600 I have never actually witnessed a cowbird fighting with a bluebird nor entering /exiting a nestbox. I did find a cowbird egg in a bluebird nest however, which tipped me off to their presence in my area. I simply removed the egg. While I realize that the cowbird is a native bird, they are becoming such a problem for some of our other native birds that measures are being taken for their control in some places. I don't think you'd get in trouble for removing a cowbird egg from a bluebird nest. Kate Oschwald Date: Fri, 04 May 2001 10:10:05 -0400 What does a cowbird egg look like? Size, shape color. Friend thinks found one in her Phoebe nest. Chased a cowbird away the other day. Thanks. H Date: Fri, 4 May 2001 12:11:38 EDT Haleya and all, From my experience the cowbird egg looks very similar to a House Sparrow egg. To me they are indistinguishable. Laura,CT Date: Fri, 4 May 2001 13:47:48 -0400 And Eastern Phoebe eggs are white. If the egg isn't white, most likely it's cowbird! Brenda Date: Fri, 04 May 2001 14:36:45 -0400 I have no experience with cowbird eggs despite my many years of birding. Might it not be safer to leave a suspicious egg in the nest till it hatches and begins to grow feathers? I myself would instantly know the difference between a baby cowbird and bluebird, but wouldn't trust myself to identify the egg. I would have no qualms about tossing a baby cowbird, once I knew for sure what it was. Just a thought, as I would hate to see us throwing out perfectly good bluebird eggs just because one looks slightly different from the rest. Dot Date: Fri, 4 May 2001 14:57:40 EDT In our area it's real common for the cow bird to lay their eggs in Phoebe nests... I used to always keep check on the Phoebe nests in the park. Linda - Ind. Date: Sat, 5 May 2001 02:41:48 -0700 (PDT) The cowbird egg is similar in size to the bluebird egg but is very dissimilar in coloration. Cowbird eggs are white with chestnut or burnt-umber spots and blotches pretty generally over the entire surface. ===== Date: Sat, 05 May 2001 08:16:39 -0400 Haleya Priest Amherst MA Whomever can tell the difference between a cowbird egg and a HOSP egg gets first prize for absolute brilliance!!!! The top is maybe a little more rounded - at best. Everything else - size, shape, etc are nearly identical! Very smart birds! :-) H Date: Sat, 05 May 2001 12:22:14 -0700 Someone wanted to know what cowbird eggs look like.. go to http://www.pma.edmonton.ab.ca/vexhibit/eggs/vexhome/egghome.htm the go to nest and pull the menu down to brood parasite (sp) and it will show cowbird eggs in nest with other eggs. Norma Zier Date: Wed, 9 May 2001 18:39:51 EDT Hello All, I realize that this is not BB related, but I could use some of your collective intelligence. I have a cardinal nest in my yard. It contains five eggs. Two of these eggs are clearly larger than the other three. One of the larger eggs has a white background with brown spots. The spots are more concentrated on the larger end of the egg. The smaller eggs have a pale green backgrpound with the brown spots. I have seen cowbirds around the place this Spring. I understand that cardinals are common cowbird hosts, Gr-r-r-r-r-r #"at"!*%x!! One of my questions..... is it likely that cowbird eggs are the larger ones..? Bruce Macdonald SW Ontario, near Detroit/Lake Erie Date: Wed, 09 May 2001 21:40:00 EDT "If we all agree we wouldn't learn anything!" NO SCIENTIFIC RESEARCH will ever explain out why something works for one person and not the other And along the same lines, I decided that there was ONE area in which ALL our bluebirds are alike: They're all different! Rhonda Watts Date: Fri, 11 May 2001 16:33:08 -0400 I'm certainly not the expert here, but from what I've read here and in the books, yes, it is likely that the larger, white/with brown spotted eggs are the cowbird eggs. VMS Brucemac1"at"aol.com wrote: One of my questions..... is it likely that cowbird Date: Fri, 11 May 2001 18:36:51 -0500 Keith Kridler Mt. Pleasant, Texas Brown headed Cowbird eggs are almost identical in size to a bluebird egg. When you mix them in a batch of house sparrow eggs you cannot tell the difference. For us down in this part of Texas the cardinals lay a larger egg that has darker colored spots than the cowbird eggs. The baby cowbirds have a very dark red mouth lining where as the bluebirds have a lighter orange shade to their mouth. I do not know for sure what the cardinals mouth lining color is but the baby cowbirds will have a white or light gray colored "fuzz" when born, once again the baby bluebirds have a black or very dark colored fuzz but I believe the cardinal young will be VERY hard to tell from a cowbird. When in doubt watch, wait and see what happens. Keith Kridler Date: Fri, 11 May 2001 20:26:06 -0700 There is new research that suggests that the color of the lining in a nestling's mouth is related to how recently it has been fed. When the bird has not been fed during a current "round", the blood is collected around its mouth, making it appear bright red. When that particular bird has been fed, the blood is drawn to the digestive area to work on the "meal" and the bright red in the mouth fades. This is how the adults can determine who is the "hungriest" and who gets the next feeding. If they see bright red in some and lighter red in the others, the bright reads get fed next. Pretty neat, huh? Judy Mellin Date: Sat, 12 May 2001 06:35:50 -0400 NO, No, No!!! Cowbird eggs as compared to cardinal's are smaller! One reference I have states cardinal eggs are 25 x 18 mm; cowbird eggs are 21 x 16 mm. A second reference states cardinal's average 25.3 x 18.2 mm and cowbird's average 21.45 x 16.42 mm. Cowbird eggs are colored very similarly to other birds' eggs. This is why it's dangerous to arbitrarily remove cowbird eggs!! (In addition to being illegal.) Bruce, I hope you didn't remove the larger eggs. Brenda Date: Sat, 12 May 2001 06:45:57 -0400 Keith wrote: I do not know for sure what the cardinals mouth lining color is Cardinal chicks: Skin is orange. Down is blackish-gray. Mouth is red; gape flanges are cream. From "A Guide to the Nests, Eggs, and Nestlings of North American Birds." Brenda Date: Sat, 12 May 2001 22:24:34 EDT Thanx for the response Brenda. I must've read the same reference book as you. It told me the Cardinal eggs are slightly larger than the cowbird eggs. Have your ever heard/read about cowburds removing an egg prior to parasitizing a nest..?? Two days ago, my Cardinal nest contained five eggs. Two were slightly larger than the other three. This evening, there were only four eggs. One of the larger eggs was missing..?? I'll watch to see if another smaller egg turns up tomorrow. Bruce Macdonald, SW Ontario, near Detroit/Lake Erie Date: Tue, 29 May 2001 17:48:44 -0500 ... I didn't notice any other eggs but only saw BB eggs in the box; however, we do have a lot of cowbirds around here and perhaps I just didn't see the egg. I guess time will tell if this is a BB or a cowbird. If this is a cowbird baby, will mom and pop bluebird keep taking care of it? I don't plan to remove the eggs yet. As I said earlier, I wasn't expecting them to hatch until around the end of the week. I'll check the box again tomorrow and let you all know what I find. Again, thanks so much for your help. It is so good to have a place to go to where you can get help when you have strange things happening. Dottie, Brown County, Indiana Date: Wed, 30 May 2001 20:19:58 -0500 I checked the BB box this morning and there was only the one baby inside still sprawled over the other BB eggs. It didn't lift it's head when I opened the box but I could see it breathing. I'm too new to tell at present if it is a BB or a Cowbird. No other eggs have hatched as yet. I will keep you posted as to what happens next. We are expecting rain for the next several days, starting tonight, so I won't open the box again unless there is a break in between storms. Again, I want to thank all who responded to my questions. I'm keeping a manual with questions and answers for future reference. In addition, all my Bluebird talk has prompted a couple of friends to put up a BB box a couple of weeks ago. They now have a full nest! I'm hoping to get them into the BB club next. To all you new Bluebirders, (I'm new also) this BB List is a wonderful place to go for information and, sometimes, sympathy. The members are very helpful and provide answers to questions immediately. Good Luck. Dottie, Brown County, Indiana Date: Wed, 30 May 2001 21:43:46 -0500 I'm sorry, Barry, but I don't have that kind of camera right now but we are planning to get one. My son has one but he's in Europe on his honeymoon. In fact, I just e-mailed him. I will also be interested in how your BB's and Cowbirds develop. I was just telling my husband about the "baby Huey" we have in the nest. Do you know if Cowbird babies act the same as BB babies? This one does not raise it's head and open its mouth when I open the box. It just keeps on sleeping like my other BB babies did. But it looks so big and the way it's sprawled all over the other BB eggs just looks kinda strange. I will keep everyone posted. Good luck. Dottie, Brown County, Indiana Date: Fri, 1 Jun 2001 13:12:35 -0500 I have some good news and some bad news. The good news is that Baby Huey is a Bluebird and not a Cowbird. I took a chance during a tiny weather break and checked the box. I couldn't stand it a minute longer without knowing. It is definitely a Bluebird. It has blue down or feathers - not for sure - but they are blue. The bad news is that the other eggs have not hatched. I thought maybe I should leave them in the box a few more days just to be sure unless you more experienced Bluebirders think I should remove them. There should be four eggs. Baby Huey is not sprawled all over them anymore but was over near a corner of the box. I saw mom and pop out near the box yesterday afternoon. We are still having bad weather here-chilly, rainy and windy. Thunderstorms are predicted this afternoon-maybe severe. Dottie, Brown County, Indiana Date: Thu, 7 Jun 2001 16:46:34 -0400 A friend of mine asked me a question about the Cow Bird which deposits eggs in Eastern Bluebird (EABL) nests. The question he asked me: during which days of the nesting cycle are the Cow Bird eggs deposited? This would certainly be very useful information in checking the nest for such parasitic eggs. Any answers would be appreciated. Thank you! Fawzi in MD Date: Mon, 18 Jun 2001 11:15:29 -0400 Hi everyone; My name is Peggy and I am from South Eastren Michigan. I have a couple of questions about cowbirds. 1. What does a cowbird look like ?? I see you all talk about them lots of times. Are they a threat to the EABB. Thanks Date: Tue, 19 Jun 2001 08:05:29 -0400 Peggy, Below is a description of the cowbird and a photo link. I've not had problems with them in the past two years in northeastern Maryland. Field Marks:A rather small blackbird with a short, conical sparrow-like bill. The Male has a brown head. The female is uniformly gray. The finclike bill is a good mark. Voice: Chuck. Also a chatter. The flight note is weeee-titi ( a high whistle, two lower notes). The song is a bubbly and creaky glug-glug gleeee with the last note being on the high pitch. Where found: United States - Mexico border to west Pananma. Habitat:Woodlands, mesquite, citrus groves, towns. Nest: "NONE"; Lays its blue-green eggs in nests of other species and most http://www.tsuru-bird.net/ Pam Ford Date: Tue, 19 Jun 2001 08:11:57 -0400 Oops, sorry the link didn't take you to the picture, but the photo homepage.
Once there go to Images, Birds, and scroll down to Blackbirds and Orioles - Date: Tue, 19 Jun 2001 10:36:19 -0400 (EDT) Hello Peggy, The male Cowbird is glossy black with a glossy brown head. About the size of a Cardinal. The female is brown and not as glossy. You need a bird identification book for this type of identification. These birds are quite common and usually don't bother nest boxes that much. When I lived in Ohio there were Cow birds around my yard most of the time, but never once in 26 years did any lay eggs in a bluebird nest. Joe Huber Venice, Fl. Charter member NABS, Charter member OBS, Life member OBS Joe Huber... Date: Thu, 28 Jun 2001 10:48:21 -0400 I've been bluebirding for 15 yrs or so and have had up to 30 boxes on my trail. Recently I found a brown headed cowbird egg in a nest of 3 Eastern bluebird eggs. I found one broken egg on the ground near the box, however this box had already fledged 4 bluebirds so this egg shell could have been from that clutch. I didn't remove the cowbird egg at that time to see how the bluebirds would react. After several days of observation I realized the bluebirds had abandoned the nest. After about 5 days the bluebirds built a new nest on top of the nest containing the 3 BB eggs and 1 cowbird egg. The hole measurements for the nest were right on 1&1/2". According to Dr Zeleny's book "The Bluebird", cowbirds in a properly constructed box should not be a problem. By the way this old, tried and true book should be required reading for anyone interested in bluebirds. Has anyone else encountered cowbird eggs in their boxes and if so how did the bluebirds react. Andrew From: "Bruce W. Wilkinson"
bwilkinson"at"multipro.com We are a new group of bluebird watchers in central TN and at one of the early meetings someone asked if anyone had experience with cowbirds getting into bluebird nests and laying an egg. If so, how can you identify a cowbird egg from an occasional white bluebird egg? From: "Keith & Sandy Kridler"
kridler"at"1starnet.com Brown headed cowbird eggs look identical to the average house sparrow egg in both size and coloration. I have yet to find a white cowbird egg and they are normally lightly speckled where as the house sparrow eggs can be heavily speckled. Cowbird young have white or cream colored fuzz when they first hatch and the bluebirds have the dark colored fuzz. Cowbird young have a bright red or scarlet mouth and throat lining while the young bluebird throat is orange when compared to the cowbird. Cowbirds hatch in about 9 days I believe and normally have a 3 day head start on growing...Keith Kridler Mt. Pleasant, Texas From: "judymellin"
judymellin"at"netzero.net Date: Fri, 2 Nov 2001 05:45:29 -0800 I wonder if speckling is also a regional phenomenon. I see cowbird eggs here
in the upper Midwest- well, at least NE IL.- that are very heavily speckled. I
have a sterile one on a bookshelf that survived a bluebird nesting and hatching
and it is as speckled as an egg can be without being a solid color. From: "Pauline, Mountain City TX" bluebirds"at"austin.rr.com Do cowbirds lay eggs in 1.5 inch hole bluebird nestboxes? If so, how much of a problem is it? Are bluebirds one of the species that would typically toss a cowbird egg? Pauline Tom From: "Bruce Burdett" blueburd"at"srnet.com Pauline, et al No. I have never see a Cowbird nest in a birdhouse of any kind. Of course, I
should have learned never to say "Never." From: "MJShearer" eshearer"at"attbi.com Hi Bruce, Pauline, and all, Cowbirds will dump an egg in a bluebird nest, and they can get in a 1 1/2 inch opening. You'll find past discussions of cowbirds in Jim's Best of Bluebird archives: http://audubon-omaha.org/bbbox/bestofbbml/bblindx.htm Just checked the boxes in my yard. I have one almost complete bluebird nest, one half finished titmouse nest, and one Carolina chickadee nest complete with female on the nest. The nest boxes are 70-90 feet apart. MJ From: "judymellin" judymellin"at"netzero.net On a bookshelf, I have a sterile cowbird egg that survived a nesting of Eastern Bluebirds. There were two eggs and one hatched before I was aware of it, yet the blues from that nest fledged just fine, even with the cowbird young! Now, before everyone says that this could not happen, I have the egg to prove it! And, this egg will not lay flat. It is raised from the narrow end to the wider end- and holds that posture, whether or not it is the vernal equinox. It is tipped up at about a 45 degree angle. Although our trail sits on a 150 acre contiguous grassland, this is the only incidence of cowbird parasitism I have ever had. Judy Mellin Date: Wed, 27 Mar 2002 15:26:13 -0800 I have read of studies of Cowbird Parisitism on Prothonotary Warblers. (I think the researchers were using milk carton "boxes" for this study!) The Cowbirds could get in all but the smallest entrance hole. So I don't think 1.5" would be a hindrance. I wonder if this behavior is triggered by a lack of "open-nest" hosts or that the individual had been raised in a nest box (or there is the inclination in its genetic line). Was that a Cornell study? I can't quite remember.... BTW: Anyone out there know of a website that lists all known hosts of Brown-Headed Cowbirds? Marsie Nufer Cowbirds in Nestboxes (Part 2) |
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