With its bill agape, I watch as the crow fans out awkwardly across the cedar shingles. Pressing the camera to my face I snap a couple photos, pleased to finally capture on film a moment I so often encounter in the field. Unlike the crow, who’s keeping a watchful eye on the sky, I’m completely taken with my admittedly creepy behavior. Until, of course, I hear the stiff “Excuse me, can I ask what you’re doing?” from the driver’s window as the homeowner’s minivan pulls up behind me.
Fortunately for me, crow curiosity isn’t hard to come by and quickly the homeowner is as taken with watching this bird as I am. “So, what is it doing up there? I see them like this on my roof all the time” he asks after I give him my credentials. It is a rather odd sight. It’s nearly 90˚ and the crows is sitting in direct sunlight, mouth open, head cocked and wings outstretched like it’s injured. Rather than escaping to shade, it’s joined by its fledgling and together they bake their bodies in the hot sun for a few minutes before gathering themselves and carrying on down to the grass to forage.
Although the specifics can vary slightly, this general kind of posture can be observed across hundreds of bird species, even those you might not expect to have much opportunity for it like owls. Often it’s used to dry wet feathers or warm up on a crisp winter morning but, given that they do it even when it modestly heat stresses them, it must have some other physiological benefits beside thermoregulation.
There are a handful of other reasons that birds may sunbathe, but the big picture is that applying intense heat to feathers is critical to maintaining them in good condition. For example, sunlight exposure has been shown to suppress feather degradation caused by the bacteria Bacillus licheniformis 1. Heat also helps control ectopatasites, possibly by making them more mobile and easier for birds to remove2. Lastly, sunning may relieve discomfort caused by molting and promote vitamin synthesis3.
So, far from being a signal of distress or heat exhaustion, observing this posture in crows is like watching them ruffle around in a puddle. It’s a routine, and important part of their self care regimen. Plus, everyone knows a few minutes in the sun just plain feels nice.Literature cited
1. Saranathan, V., and Burtt, E.H. Jr. (2007). Sunlight on feathers inhibits feather-degrading bacteria. The Wilson Journal of Ornithology 119: 239-245
2. Blem, C.R., and Blem, L.B. (1993). Do Swallows sunbathe to control ectoparasites? An experimental test. The Condor 95: 728-730
3. Potter, E.F., and Hauser, D.C. (1974) Relationship of anting and sunbathing to molting in wild birds. The Auk 91: 537-563