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Discussion of other Raptor species; their anatomy, biology, ecology, etc.
Topic Started: Sep 16 2007, 11:04 AM (18,108 Views)
ostrich2
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Here is an interesting story about a barn owl:

Wedding Rings Duties For Barn Owl
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Raptorman
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ostrich2
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Raptorman,Jan 3 2008
12:39 AM
Using the same simple techniques years ago I did a commercial for a fast food chain in Georgia (I think). A MacDonald's type setup with order taking speaker and pickup window. My Barn Owl's job was to be sitting on the order speaker, vocalize a pretend order, fly down the driveway and grasp the order in a company bag while flying past the clerk at the pickup window and off into the wild blue yonder. I have a copy of the commercial somewhere and will see if I can post it on PhotoBucket. Bill :D

That's pretty interesting - is there any particular reason they decided to use a barn owl for the commercial? I'm imagining a barn owl is a little bit of a relatively less known species to the average viewer - I'm mildly surprised they didn't want to use a hawk or something more familiar to the casual viewer.
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Patti
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Bill, looking forward to your commercial video! My friend has had a wild-caught Umbrella cockatoo for years who has been in a number of TV commercials. His name is Judy (from previous owner) but we call him Toot. Will still bite and be nasty if he feels like it and VERY aggressive while in the hormonal mode, so not to think he's a sweet dear fellow all the time. No, he isn't--just for the record. A good bird, but still a wild beast. :lol:
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ostrich2
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I know when I read Peter's posting about some of the Catalina birds skipping egg laying I was thinking a bit about some of those factors. I wonder what it might have been in these specific cases - we know the Channel Islands provide plentiful food and territorial resources for the balds, and presumably the population is still well below the maximum carrying capacity for the area, so I regarded food availability as less likely. Disturbance can always happen I suppose and it's hard to predict when/how this may occur, but I did get the general impression that human activity at least on Catalina in the areas where the actual nesting territories are located is quite minimal. That's why I had wondered whether this is occasionally due to no particular "external" cause at all, but one in which something hormonally/physiologically doesn't quite happen right and the process is skipped.

I did check Stalmaster on this topic, and it does briefly mention this topic indirectly:

"The Bald Eagle: Mark Stalmaster (1987) pg 56"
 

The clutch size - the number of eggs laid in the nest - ranges from one to three (Fig 5.5). Clutch sizes of four have been recorded, but they are thought to be the result of two females laying eggs in the same nest. (4) The vast majority of clutches have two eggs.  The average clutch size, based on hundreds of nests, varies from 1.90 to 1.97, or just under two eggs. (10,22,23,25,50,52).  The number of eggs laid is predetermined: if eggs are removed, eagles usually will not continue laying to fill the clutch and will incubate only the ones remaining. But if all eggs are removed, they will likely relay an entirely new clutch


Unfortunately Stalmaster does not delve specifically into the topic of when and under what conditions balds might skip egg laying, although some of the references may discuss it. The comments in the blog certainly imply that this is a "known" trait of balds, in which case if true I assume there would be some sources that document it, (including ones of course more recent than Stalmaster) but I don't have any of these handy.
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I would actually tend to make a distinction between several different statements in the blog. In particular I regard the question of what the bald's behaviour actually is on this topic as separate question from what the reason/causes for that behaviour would be.

In the blog, there are several different things mentioned. I don't know who the author is either, although even if he does not have any specific professional expertise with balds I wouldn't tend to necessarily dismiss the possibility that the information is drawn from valid sources. On one hand the blog kind of implies that some of these traits are "well known" and thus probably scientifically documented, while on the other he seems to mention some of his own personal observations, which may or may not apply to the species as a whole.

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The first, unfortunately, is that Bald Eagles are famous for being productive for two or three years (sometimes, only in a single year) and then they take a year off.


Not being an expert on the bald, I don't know whether this is true of the bald or not, but at least it does not seem to be in and of itself totally implausible or out of the question. I wouldn't tend to dismiss the idea out of hand anyway.

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They go through all the motions of laying eggs, but simply fail to do so.


This is actually a description of a quite specific behaviour, which if it happens I would think would be quite easy to identify.

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It's a normal part of their biology. This tends to happen more frequently following a previous year's production of three eaglets.


This is a statement about the specific conditions that are correlated to the behaviour - assuming the behaviour does occur, that it might be related to activity the previous year might be possible.

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This apparently wears out the parents and they then sometimes take a year off.


This by contrast is a statement about the actual reasons/causes for the purported behaviour. This I do find much more implausible - if the behaviour does occur, it doesn't make a lot of sense to me that it would be because of "fatigue". That strikes me as projecting a human interpretation on the behaviour. Even "fatigue" if it exists would have some physiological source. If you say "a human being can run a maximum of a few miles before tiring", there are actual physiological reasons why this happens (the lungs can no longer supply sufficient oxygen, the muscles build up lactic acid , etc). If the eagles were "tired" I can't imagine what such a reason could be - the nesting seasons are months apart, and it's not like egg laying is such an intensive process that you would expect to have some long term effect on a healthy bird.

On the question of stringing out laying, I take it that implies removing eggs while the clutch is partially laid, not after all eggs have been laid as a group. There are a number of references cited by Stalmaster, but I assume that any data on balds on this question would have to have been collected from captive situations. I can't imagine how you could effectively measure a stringing out process in the wild. This citation from Stalmaster is about captive balds, so that's a good candidate for such information:

1973. Captive propagation of bald eagles (Haliaeetus leucocephalus) -- A review. International Zoo Yearbook 13:244-49.
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Patti
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Bill & Ostrich: after I read your thoughts on bald eagle "burnout," I Goggled failed bald eagle nests and found this info. I checked into this Tucson, AZ website after and it seems pretty neat. Also, they have a Sources link at the bottom of the page I've posted here. It didn't really tell me about egg-laying, but I thought I would post here and have cross-posted in Chat.

After you open the link, you can go to California and read a bit about our Channel Islands eagles. Keep in mind, this is only the LOWER 48. Cannot see it well, but Washington state has 835 pair.

Center for Biological Diversity
Bald Eagle Population Exceeds 11,000 Pairs in 2007


http://www.biologicaldiversity.org/swcbd/species/eagle/

Long-term trend for each state available for first time
Most recent count of eagle pairs in the lower 48 states


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Patti
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Bill: Thanks! Also, there was an interesting page on the status of the Arizona bald eagle...which nests in the winter...link posted below. Apparently many in Arizona are not happy with taking it off the endangered species list in Arizona. I can see why.

Desert Nesting Bald Eagle--Center for Biological Diverity

Taken from the Map page: "The bald eagle of the Sonoran Desert is unique among all other bald eagles in that it nests during the wintertime."
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