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For those of you who missed John's terrific explanation of this behavior, here's a sample. I hope I can repeat his words accurately.
Birds with dark plumage do this to raise the body temperature to a point where it would kill certain insects. White birds will never raise the temperature enough, that's why they don't bother with this.
Interesting explainning for this behaviour.
You have it right Fabs. Nice image of sunning behaviour. I'll try to dig up one I have of a Brown Noddy doing the same thing. To add a little to what Fabs said: most/all birds carry a suite of parasites in their plumage. These are feather lice, ticks, and the like. Work on dark-plumaged birds such as noddies has shown that when they "sun", the temperature in their plumage rises to a level which is lethal to these ectoparasites, as they are called. White/light coloured birds reflect most of the radiation back so have trouble raising the temperature to lethal levels.
..... so what do white birds do? Must have a different way of dealing with parasites !!!
Woah! Love the eye detail here Fabs. Wonderful job in explaining to us about the parasites.
Al, Good question. Inquiring minds want to know.
Sharna
Good question Al. Light/white birds may on average carry higher parasite loads than dark birds but there may not be a huge cost to this as good parasites don't harm their host. It is possible that individual birds only "sun" if they detect they have a heavy burden so it's more an individual band-aid measure rather than species-specific activity. Maybe light birds preen more and preen each other more (allopreening).
Here's an example of Brown Noddies at my study colony in Culebra, Puerto Rico, sunning. They cock their tail to the right or left and lay an outstretched wing over the tail. You can imagine they get pretty hot in full sun at 18° north latitude, 90°F/32°C in shade, dark rocks behind and dark plumage! The birds show signs of heat stress when they do this (panting) but they do it anyway. When they measured temperatures within the plumage of Black Noddies doing this I think they got 113-122°F/45-50°C! I'll check the paper.
Image is from scanned Kodochrome-64 slide (those were the days), taken in about 1986. The metal object above the bird is a stainless steel numbered tag we used to mark nest locations.
Thanks for the explanation, John, great example too :)
I see Turkey Vultures doing this all the time and have also seen Calfornia Condors doing it as well. Thanks for the explanation John.
Steve
Here are my contributions. Some time ago I found a family group of barn swallow, or maybe two families, displaying an interesting behavior. All the birds were flying very low, near the ground and began to perch on the sand and spreading tails and wings, facing to the sun (no dust bathing in any moment). I think that this is another example of the same behavior and, by the way, the sun was really burning the birds:eek::eek::eek:
I observed this behavior about ten minutes.
The first example is a young bird and the birds in the second image are both adult birds. I think that they were full loaded with bugs after the nesting ;)
A couple of adult birds under a torrid sun
Interesting thread. Is this bird doing the same thing (great blue heron with its underside wings pointed to the sun):
http://www.clarkvision.com/galleries...744.d-750.html
Roger
I think you GBH is practicing yoga Roger.:D
Very nice image.
Steve
Interesting discussion. I knew about sunning behavior which has been documented in over 140 species of birds. The thermoregulatory function never seemed sound except perhaps in colder environments but the parasite killing hypothesis also seems somewhat weak. Preening is the first defense against ectoparasites though some exotic behavior such as anting (letting ants run over the feathers) is thought to kill parasites also.
Observations in zoos have shown that many species of birds will sun under the same conditions irrespective of size or color. To believe that they are all similarly heavily loaded with ectoparasites and invoking the same behavior at the same time seems like a long shot.
Other hypotheses in the literature include thermoregulation, dealing with moult, drying feathers and so on. None though seem to explain this behavior very satisfactorily. The function of dusting in birds isn't so clear either. Complex behavior like this isnt so easy to interpret and probably serves multiple functions.
I agree Barry- there is usually never just one explanation for everything.
Here's the paper I referred to on Black Noddies:
http://elibrary.unm.edu/sora/Auk/v11...1073-p1077.pdf
I was low on the plumage temperatures attained when noddies sun- up to 72°C/162°F! You could probably cook an egg at those temperatures.
Roger- This is the classic heron sunning pose. Someone a week or more ago posted a similar image of a night-heron doing the same thing.
Quote:
Originally Posted by rnclark
John, yes i saw that paper. Really good stuff. Here is another that shows you that similar looking behavior can be caused by different precipitating events
http://icb.oxfordjournals.org/cgi/co...tract/28/3/845
