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Bergmann's RuleFrom: Peter Kwa [mailto:kwapeterca"at"yahoo.ca]
Sent: Monday, January 15, 2007 9:31 PM Subject: Bergmanns Rule and more OP (Ontario Pete) in Canada, sorry long!
Bergmann’s Rule says that warm-blooded animals of the same species are bigger when they live in colder climates compared to those living in warmer climates. Whereas the Rule may not apply to migratory birds such as the various species of bluebirds, I wonder whether the Rule applies to non-migratory birds such as the House Sparrow (HOSP). This is relevant to the hole size required to exclude the HOSP. I could find the following anecdotal evidence that the Rule does apply, as follows.
(from www.sialis.org/hosp.htm) Frank Navratil of IL with a cold continental climate determined hole size thresholds between allowing and excluding HOSPs:
ROUND
1 1/4" diameter allows HOSP entry. 1 1/8" diameter stops entry. However, Phil Berry of balmy FL reported HOSP entering via a 7/8"!
HORIZONTAL SLOT
1 1/2" x 1" slot allows entry. 1 1/2" x 7/8" stops entry. VERTICAL SLOT
1" x 1 1/2" slot allows entry. 7/8" x 1 1/2" slot stops entry, however one Mike (sorry, I don’t have his last name) of balmy Seattle had a HOSP build a nest in a Violet-green Swallow box with this slot size! (end www.sialis.org/hosp.htm) Another non-migratory species with a large latitudinal range is the Black-Capped CHickadee (BCCH). There is again anecdotal evidence from local birders here, that at least some Canadian BCCHs have problems entering the 1 1/8” diameter hole often promulgated, I believe, by US sources. Since I want to attract BCCH to a nestbox while excluding the HOSP, I did not want to simply enlarge the hole, but have approached the issue as follows.
I have carefully watched videos of UK Blue Tits (a species related to the BCCH) how they go through the entrance hole. Without going into much detail, the crux of the matter is that the birds need legroom to push their torsos through the entrance hole. I do not have any videos on bluebirds to carefully watch, but this may explain why bluebirds go through the Peterson oval hole size of 1 3/8” x 2 1/4” although it is narrower than the 1 1/2” diameter round hole. In other words, the 1 1/2” diameter round hole appears to restrict the bluebird in the vertical rather than in the horizontal dimension. I suspect very much that this holds true for the BCCH (and mutatis mutandis perhaps for other bird species as well) namely that a 1 1/8” round hole restricts the BCCH in the vertical rather than in the horizontal dimension, and hence, that an (upright) oval hole is more appropriate by giving the bird the legroom it needs for pushing its torso through the entrance hole.
Consequently, I have opted for an oval hole size of 1 1/8” x 1 1/2” for my BCCH box which oval hole I made as follows. I started out with a NABS-style bluebird box with a 1 1/2” diameter round hole. I took a metal hole reducer place with a 1 1/8” diameter round hole, but cut it out with a Dremel tool to a n-shape with the legs of the n-shape spaced 1 1/8” apart and with the 1 1/8” diameter arc at the top. Aligning the top of the n-shape to the top of the round bluebird hole results in the oval 1 1/8” x 1 1/2” hole. I have opted for an n-shape rather than a u-shape (i.e. mounting the n-shape upside down) to leave wood exposed below the entrance hole for the birds to cling to with their toe and toenails, since with a u-shape there would be a slippery metal surface below the entrance hole. A detail which may or may not have any bearing on the form and size of hole issue is that the box came with a wooden predator guard installed, so that the tunnel behind the metal plate is 1 1/2” deep.
My hope is that all my local (Canadian) Bergmann-Rule-enlarged BCCHs will go through the oval 1 1/8” x 1 1/2” hole. My fear is that such oval hole will not exclude a Frank Navratil HOSP which goes through a vertical 1" x 1 1/2" slot or a Mike HOSP which goes through a vertical 7/8" x 1 1/2" slot. However, my further hope is that my local (Canadian) HOSPs are Bergmann-Rule-enlarged as well so that they cannot go through the oval 1 1/8” x 1 1/2” hole.
I truly hope that my local HOPS have read their Bergmann’s Rule, but kidding aside and in summary, I would like to toss up the following discussion topics:
Does Bergmann’s Rule specifically apply to the HOSP and if so, to what quantifyable extent?
Are there any studies correlating HOSP-excluding maximum hole size to the local minimum annual temperature, latitude, continental climate, coastal climate, etc?
Does Bergmann’s Rule specifically apply to the BCCH (and other bird species) and if so, to what quantifyable extent?
Are there any studies correlating BCCH-allowing minimum hole size to the local minimum annual temperature, latitude, continental climate, coastal climate, etc?
Are there any studies on oval holes for other species than bluebirds?
Again, sorry for the long post. From: Keith & Sandy Kridler [mailto:txbluebirder"at"sbcglobal.net]
Sent: Tuesday, January 16, 2007 8:48 AM Subject: Re: Bergmanns Rule and more Keith Kridler Mt. Pleasant, Texas
This rule applies more to animals than it does to birds. There is a huge variation in the sizes of many immature animals compared to their parents where as MANY young about to fledge birds weigh as much if not more than their parents.
When trapping and weighing House Sparrows we did not see much variation in the birds as adults. BUT House Sparrows kept in a live trap could lose 25% of their body weight in just about 24 hours. House Sparrows by the way weigh about the same as five US or Canadian quarters.
One thing we have found with Carolina Chickadees is that when given the option of using 1&1/4" entrance holes or the 1&9/16" round holes they always used the larger holes for the past three years. They & tufted titmice preferred higher mounted nestboxes in the 8 foot to 14 foot height over boxes mounted 4 feet to 6 feet off the ground. We fledged way more of these species on our 30 acres where we have about 100 nestboxes of various sizes at various heights with various sized entrance holes compared to 300 nestboxes widely spaced along roads. The smaller cavity nesters are more likely to be evicted by bluebirds than they are House Sparrows.
Wood duck nestboxes in Minnesota have the entrance holes 4" wide by 3" tall as birds are the widest at the edges of their shoulders than they are top to bottom. If you use a micrometer on the birds you capture you will see this applies to House Sparrows, Bluebirds ETC. KK ...o Ohio. From: Bet Zimmerman [mailto:ezdz"at"charter.net]
Sent: Tuesday, January 16, 2007 10:51 AM Subject: RE: Bergmanns Rule and more Wow, here's a post that woke me up from hibernation!
RE Bergmann's rule, we've had discussions about starling size variation based on location, with folks in some areas having major problems with access to Peterson oval holes in some locales and not others. (Here in NE CT I have not had a problem to date, fingers crossed, might just be a matter of time.)
With regard to HOSP, the biggest ones I ever saw were in Richland WA - at first I didn't even think they were HOSP. About same latitude as here, warmer overall.
With regard to BCCHs, in my personal experience, I find they won't select a box that has a 1 1/8" hole reducer on it - preferring the 1.5" (I have not had any BCCH nestings in Peterson's to date.). After they lay an egg I add the hole reducer to protect them from HOSP, and they go on to successfully nest. I added your comment on Canadian BCCH's to my All About Black-Capped Chickadees page at http://www.sialis.org/chickadee.htm, thanks for the info.
RE Oval holes, I gather from what I've read that the thinking on that design was it better conforms to the bluebird's body shape.
RE your research questions, I just added them to the list I'm keeping of topics I think we need more info on for now, at http://www.sialis.org/research.htm, although there may be some stuff in Birds of North America....
Bet from CT
... From: Torrey [mailto:torrey_canyon"at"yahoo.com] Hi Pete in Ontario, Your questions could be best answered by the Bird Banding Lab. The US office is at the Patuxent Wildlife Research Center in Maryland -- I'm not sure where the Canadian office is. All the data (typically age, sex, weight, wing length, maybe tail length, maybe fat score, & of course band number) from any project is sent to the Banding Lab, where it can be accessed by any scientist. We run 40-50 mist nests here (southern Michigan, halfway between Chicago & Detroit) seven days a week during fall migration & band 8-10 thousand birds. We also have a summer banding program (Monitoring Avian Production & Survivorship), which has fewer nets, operates fewer days per week, & catches just a couple thousand birds. Since chickadees don't move much, it wouldn't matter if you got fall or summer data, just so long as you're consistent. (Chickadees don't put on the huge amounts of fat a migrating bird does -- I've held some thrushes that feel more like a water balloon than a Unfortunately, i'm not sure how you query the Banding Lab. I just handle the birds -- All the data entry & data submittal is done by our head bander. But it should be a very easy question to answer -- You just look at average weights of your particular species at widely spaced banding stations. If you do find anything out, let us know. yours, Torrey Torrey Wenger From: Peter Kwa [mailto:kwapeterca"at"yahoo.ca]
Sent: Tuesday, January 16, 2007 4:03 PM Subject: Bergmanns Rule and bird brains OP (Ontario Pete) in Canada says thank you for the welcome and the responses on and off the list! And a special thanks to Bet Zimmerman for the ‘best of bluebird-l’ archives and the sialis.org web site. They are truly marvelous resources, and most of all, am I glad that other cavity nesting birds are included! It is also a nice surprise that a comment from a beginning backyard birder like myself makes it to the sialis.org web site. It is a good thing, that the comment has been qualified as anecdotal evidence which it truly is :-) --------
On the comments that chickadees prefer bigger hole sizes such as a 1 1/2” or a 1 9/16” diameter round hole when selecting a nestbox: thanks for the suggestion, I will take the metal hole reducer plate off and put it back on after the first egg has been laid (as protection against the HOSP). Interesting, that there appears to be a bird brain factor at play here which dominates physical torso size factors.
In the same vein, are there any indications that chickadees prefer a short 3/4” tunnel over a long 1 1/2” tunnel? In other words, shall I take the wooden predator guard off my box too? (My NABS-style bluebird box came with a wooden predator guard already installed, i.e. the hole diameter is 1 1/2” and the total length of the tunnel now is 1 1/2”)
Birds of the cold may like the vast sky and may dislike long tunnels into their nesting cavities … Bergmann’s Rule for bird brains. Kidding aside,
What are the dimensions of a natural nesting cavity of a BCCH (and other bird species) ?
What is the diameter of the tunnel?
How long is the tunnel?
It is more than likely that Cornell, USGS, CWS, CWF, and others already have the raw field data. I’m hoping that they have processed the raw data to extract from it useful information for practical use. From: Peter Kwa [mailto:kwapeterca"at"yahoo.ca] Sent: Wednesday, January 17, 2007 9:21 AM Subject: re: Bergmann's Rule and more On bird banding lab: the raw data will need to be processed to extract useful information from it. This is a sizeable amount of effort, and I wonder if a scientist would spend the effort.
The main benefit, as I see it, is information on local size variations of desirable and undesirable species. This information can then be used for the determination of size and form of entrance holes for maximum selectivity, which determination may vary from locality to locality. From: Bet Zimmerman [mailto:ezdz"at"charter.net] Sent: Wednesday, January 17, 2007 1:28 PM Subject: RE: Bergmanns Rule and hole depth There is a wealth of data out there, but I'm not sure how much of it has been mined. I remember a study of U.S. Army data - something like 96% of resources were spent on collection and 4% on analysis.
A while back I had posted a request for what kinds of results people on the Bluebird_L would like to see pulled from the Cornell Birdhouse Network database. Tina was willing to look into it, and possibly write an article for NABS. But I didn't get any responses....
In terms of natural cavities used by Black-capped Chickadees (hard to imagine they can excavate their own with that teeny beak!) I read that cavities they excavate are generally 5" deep x 2 3/8" wide. Both the male and female excavate, and it takes them 7-10 days. Keith reported that chickadees have nested in a log that was only 2" in diameter. Chickadees are very secretive during nesting season, but if you see one dumping wood chips somewhere, you may be able to follow it back to an excavation site.
I haven't seen anything definitive on the impact of nestbox preference or utilization by depth of hole... A lot of people use wooden block hole guards that increase the depth. Some people say Tree Swallows don't like that, some people say House Sparrows do like it or don't like it...it's a good question. There is concern about the amount of time it takes to feed through a deeper hole, and wear and tear on feathers.
I have seen some cross-section photos of woodpecker nest excavations - some make a little tunnel that goes into the nesting cavity. see photo here: https://www.denix.osd.mil/denix/Public/Library/NCR/Documents/RCW-fact-sheet-Aug06.pdf of a red-cockaded woopecker nest. This would certainly help to prevent predation by large birds or raccoons.... Some folks on the list like Evelyn do use the wooden blocks to prevent starling predation.
The only natural cavities I have seen chickadees using (I'm not very observant though) are hollowed out, rotten fence pots that are open on the top.
Bet from CT
From: Peter Kwa [mailto:kwapeterca"at"yahoo.ca] Sent: Wednesday, January 17, 2007 3:59 PM Subject: Re: Bergmanns Rule and hole depth I am certainly all for a more balanced than 96%-4% effort distribution, how about 50%-50% between data collection and analysis? It would seem to me that pretty well all the research questions posted on the sialis.org web site deserve practical answers. It would be ideal if the scientists themselves are interested in finding practical solutions for their own backyards/trails. ----------
I found the following pictures on the Ontario government web site showing a typical natural nest of a BCCH http://wildspace.ec.gc.ca/life.cfm?ID=BCCH&Page=Nest&Lang=e Makes me wonder what the cavity behind that entrance hole looks like. Does it go inwardly first, or does it right away go down or sideways? If it goes inwardly first, how far inwardly? Or do the BCCHs excavate the cavity following the rotten wood? Do wood in snags rot in certain compass directions more than in others? Analysis, please, analysis!
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Artificial nestboxes have simpler geometries than natural cavities. But box sizes given by various sources are often ambiguous. Take for example, box depth. Some sources define it as the height measured from the top of the floor to the bottom of the hole. Some sources define it as the height measured from the top of the floor to the centre of the hole, while not mentioning the size of the hole. Some sources mention but do not define the term box depth at all. Not sure though what to do about ‘disambiguation’ to borrow a term from Wikipedia.
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to Bruce and all, I am in Ontario, Canada. I did not include the location information in my previous posting, but I did so in the ones before.
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to Bar, please look at my previous postings before making any accusations, I am certainly as interested as anyone else is in preventing predation of backyard tenants. From: Bet Zimmerman [mailto:ezdz"at"charter.net] From wikipedia.org "Adult females have an average wingspan of about 7 feet (2.1 meters); adult males have a wingspan of 6 ft 6 in (2 meters). Adult females weigh approximately 12.8 lb (5.8 kg), males weigh 9 lb (4.1 kg). The smallest specimens are those from Florida, where an adult male may barely exceed 5 lb Quite a variation! Bet from CT From: Robert Barron [mailto:rebarron"at"gmail.com]
Sent: Friday, February 02, 2007 6:49 PM Subject: Re: OT: Bergmann's Rule - Eagles ... In addition to Bergman's rule (do we really understand if there are "rules" in nature?), this demonstrates the general "observation/rule" that female raptors are larger than males.
Interesting discussion. Why not in songbirds, or mammals?
Rob Barron
Fredericksburg, VA
From: Bet Zimmerman [mailto:ezdz"at"charter.net]
Sent: Friday, February 02, 2007 7:51 PM Subject: RE: OT: Bergmann's Rule - Eagles I think with most raptors, the female is about 25% larger than the male...not sure why this doesn't apply to songbirds.... Certainly a big difference in size for Bald Eagles as you go from North to South!
Bet
From: Torrey [mailto:torrey_canyon"at"yahoo.com] Female raptors are generally bigger than the males because she incubates the eggs (or broods the young) & is fed by the male. She has to bully him to actually get the food, sometimes, & any good bully knows that it's better to be big. :-) Red-tailed Hawks have no size difference, so it's not a class-wide rule. Songbirds have got different temperments & different habits. So do ducks & shorebirds. It's actually a better question "Why are raptors different?" From: Keith & Sandy Kridler [mailto:txbluebirder"at"sbcglobal.net] Keith Kridler Mt. Pleasant, Texas Wow we warmed up to 63*F today. Then they flew across the street into a massive oak tree right next to our truck and continued on with their sex education class for the whole neighborhood to see...... I had just got done explaining that the male hawks were a lot smaller than the female when we observed this display up close and personal......After several exhibitions Shawn said, "Well they look the same size to me, do we have two females or two males?" Nice to know that male and female hawks can be the same size:-)) Since it was warm and sunny the bluebirds were sitting on or near nestboxes everywhere today.KK From: charlene anchor [mailto:charleneanchor"at"msn.com]
Sent: Tuesday, February 06, 2007 6:05 PM Subject: OT - male and female raptor size differences Charlene Anchor
East Central Illinois
Sometime in the past I read explanations about the size differences between male and female raptors. I didn't remember where I read them so I checked into Paul Johnsgard's "Hawks, Eagles and Falcons of North America". He discusses this in a small section of his book. It turns out that there are various theories but nothing is certain. Ornithologists have put forth theories supported by their research and then someone else comes along with an equally plausible theory supported by what they think their research has shown. One known fact is that the greatest size difference exhibited is typical of the most highly effective predators - the accipiters and the falcons. The Red-tailed Hawk being a buteo, doesn't fall into either of those categories. But there is still a size difference between the male and female Red-tail. The average wingspan of the male is shorter than the average wingspan of the female. The average length of the male is shorter than the average length of the female. But there is an overlap and because of that some Red-tail pairs can be close to, if not, the same size. On the other hand, if a small male and a large female pair up, they will be different.
I'll quote the last two sentences in his discussion: "It is apparent that this fundamental question has not been answered to the satisfaction of all ornithologists, and indeed a single answer to the question of reversed sexual dimorphism in raptors may not be the most appropriate solution to anticipate. Let it suffice to say that the study of foraging ecology in hawks is still indeed an actively growing and changing one, and viewpoints firmly held today may well be discarded tomorrow as new information becomes available."
Sounds a little like Bluebird-L as we put forth our theories. There are surely more than one answer or solution to our questions and problems.
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