My late colleague Jack Christian documented barn and tree swallows taking the low spread-wing posture, exposing their wings fully, on metal barn roofs on hot summer days. I also saw a few instances. One possibility is that direct heat helps drive out feather parasites and exposure to UV and heat may decrease bacterial load on the feathers. Actual sunning for body warmth seems very unlikely because, like an anting bird in the sun, they often pant and look, if anything, heat stressed.
So I favor the interpretation that they are trading off their own excessive heating against what it might do against arthropod or bacterial parasites. I love the mousebird story--they are truly strange and wonderful little birds that I only partly appreciated when I lived in South Africa so long ago. Anne On May 31, 2013, at 7:01 PM, Suan Hsi Yong wrote: > On May 12, our SFO group at Arnot saw a brown creeper do the same pose but > vertically on a trunk, remaining fully camouflaged when doing so. I wish I > had my camera then. Anyhow, I assumed it was sunning itself, a reasonable > assumption on that cool day (40s-50s). The fact that your gnatcatcher did it > on this 90-degree day makes one wonder if something else is going on. > > In South Africa I saw a speckled mousebird sunning itself in what I thought > was an odd posture: > > http://suan-yong.com/s.africa.php?s=Mousebirds&k=101618 > > I later learned that this was common behavior for mousebirds and helps warm > the stomach to digest the leaves it eats (digesting leaves is slow and > inefficient and tends to work best in cow-sized beasts with multiple > stomachs, not easy to pull off in a bird, though the hoatzin has managed it). > > Suan > -- > Cayugabirds-L List Info: > Welcome and Basics > Rules and Information > Subscribe, Configuration and Leave > Archives: > The Mail Archive > Surfbirds > BirdingOnThe.Net > Please submit your observations to eBird! > -- -- Cayugabirds-L List Info: http://www.NortheastBirding.com/CayugabirdsWELCOME http://www.NortheastBirding.com/CayugabirdsRULES http://www.NortheastBirding.com/CayugabirdsSubscribeConfigurationLeave.htm ARCHIVES: 1) http://www.mail-archive.com/cayugabirds-l@cornell.edu/maillist.html 2) http://www.surfbirds.com/birdingmail/Group/Cayugabirds 3) http://birdingonthe.net/mailinglists/CAYU.html Please submit your observations to eBird: http://ebird.org/content/ebird/ --
