Excerpts from Jim Conrad's
from the June 9, 2007 Newsletter issued from Sierra Gorda Biosphere Reserve, QUERÉTARO, MÉXICO
TURKEY VULTURES SUNBATHING ON A VERY HOT DAY
Several times I've seen Turkey Vultures with their six-ft-long wingspreads "sunbathing," and I've always figured it was for the reasons usually given in books: To dry feathers and warm the body to help digestion. However, last Saturday afternoon as I sat next to my tent gazing across the reservoir I saw three vultures sail onto the lake's opposite shore, two of them hobbled down to the water and drank for a minute or two, and then all three turned their backs to the sun, spread out their wings, and sunbathed for about 15 minutes.
Here is what made me scratch my head: As I sat there the temperature in the shade was exactly 99° (37° C). Across the lake on the sunny bank almost perpendicular to the sun's incoming rays -- if my readings made other times in similar situations can be a guide -- it was at least 115° (46° C).
The birds didn't have a morning's dew to dry off their feathers, they hadn't bathed at the water's edge, and I doubt their intestines needed more heat for better digestion.
I suspect that the advantage a vulture might enjoy sunbathing in such heat is that it might encourage some external parasites to abandon ship, or maybe die from the heat, or at least weaken so that they can more easily be dislodged by preening.