Thursday, August 04, 2005

Wing-drying? Thermoregulating?

(click for larger version)

At Nine Springs a few days ago, this Great Blue Heron was standing with its wings open for several minutes at a time. It would close them for a short while but then repeat this display. I don't recall seeing this behavior before and given the hot weather, I'm wondering if the bird was simply regulating its body temperature?

Here are explanations I received from various members of the Wisconsin Birding Network:

"I've also seen this behavior and was puzzled about it. It was so strange that I made a small sketch (which I do VERY rarely) in my field book. We saw the heron just after completing our canoe breeding bird survey at Red Cedar Lake near Cambridge one year, so it would have been mid-morning in June sometime. I don't recall that there was anything extraordinary about the weather, either really hot or really cold. The bird was standing on a branch facing the sun."

"I believe when birds do this it's called 'sunning'. Mostly I've seen song birds doing this. They usually spread all their wing feathers out and puff all their body feathers out and then stare up at the sun. Biologist don't really know the reason other than maybe it helps kill parasites that bother the birds. I have a photo of a chickadee in my back yard doing this in late June. It looks very bizarre, like the birds hypnotized."

"I saw a Great Blue Heron exhibit a very similar pose (his wings held more in a 'basket' like in the picture submitted by Jeff Bahls) in Florida two years ago during the Space Coast Birding Festival. I also thought that he may be thermoregulating, but wasn't sure. We were able to capture it on video - very interesting!"

"Of interest to me is that the only time I have observed this behavior in Great Blue Herons is when I have previously seen them wading deeper into the water than they typically do - which makes me lean toward thinking that it has to do with wing-drying."

"According to Sibley, Studies of Cormorants who do this frequently have revealed no correlation between the spread-wing posture and air temperature. The article goes on to suggest they spread their wings just to dry them and a study of flightless Cormorants showed no significant change in body temperature as a result of this posture."

Link: All about the Great Blue Heron from Cornell Labs

Great Blue Heron image © 2005 Michael Allen McDowell

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