Path: utzoo!utgpu!news-server.csri.toronto.edu!cs.utexas.edu!helios!tamuts!e343gv From: e343gv@tamuts.tamu.edu (Gary Varner) Newsgroups: rec.birds Subject: Re: The buzzards of Hinkley Summary: Why vultures sun themselves in the morning Message-ID: <10775@helios.TAMU.EDU> Date: 10 Dec 90 20:05:40 GMT References: <1990Dec9.010930.15344@redpoll.neoucom.edu> <2510@mentor.cc.purdue.edu> <1990Dec10.170017.26347@midway.uchicago.edu> Sender: news@helios.TAMU.EDU Distribution: rec.birds,usa Organization: Texas A&M University Lines: 57 >>On numerous occasions I have seen a group of vultures perched in a tree >>in the early morning with their wings spread cormarant style, >>presumably warming themselves. An impressive sight. > >I've heard they do this to kill bacteria (the UV rays kill bacteria, I >guess)--does anyone know if this is true? I've never heard the bacteria story before, but at the raptor center I volunteered at we were taught that they sun themselves in order to get vitamin D. The sunning stimulates an oil gland at the base of the tail, exposure to the sun produces vitamin D in the oil (much as exposure of our skin to the sun produces vitamin D from pro-vitamin D), and the vulture ingests the vitamin D when it subsequently preens itself. Vultures are quiet in the morning because they need thermal updrafts for their foraging flights. They are large, heavy birds (four or four and a half pounds, as I recall -- your arm would really get tired holding one) and they search for carrion by flying with relatively few wing flaps, which is only possible later in the day when the same sun-driven convection which gives us afternoon cumulus clouds (and, eventually, thunderheads) is operative. Notice that they often gain a lot of altitude by flying in fairly tight circles. What they are doing is catching a cell of hot, and therefore rising air, and sticking with it until they get up high. At which point, like a glider pilot, they can set off for a distant spot in a long shallow glide. I've always wondered how different a nation we might have become if the turkey vulture -- a shy, quiet scavenger -- had been our national bird, rather than the bald eagle -- a noisy, aggressive raptor (*) . . . +---------------------------------------------------------------------+ | Gary Varner "It's too late to die young." | | Department of Philosophy -- Gregg Brown | | Texas A&M University | | College Station, TX e343gv@tamuts.tamu.edu | +---------------------------------------------------------------------+ (*) Before this remark touches off another semantic frenzy like my earlier unguarded remark about "hawks" vs. "accipiters and falcons" (I meant the buteos, by the way, I was speaking carelessly), let me emphasize that the vultures and condors _are_ raptors. "Raptor" is actually a functional rather than a phylogenetic category. The owls on the one hand and the hawk and falcon families (which includes everything from eagles and buteos to kites and kestrels, _as_well_as_ vultures_and_condors_) are now thought to be examples of convergent evolution: both categories of birds developed keen eyesight, strong feet with sharp talons, and sharp, hooked beaks, because they lead similar lifestyles (catching and killing fast moving prey). The vultures still have keen eyesight and sharp, hooked beaks for tearing flesh, but they have lost the strong feet the other raptors need for catching and killing their prey. Since vultures eat carrion, they don't need strong feet, and since they spend a lot of time on the ground (unlike other raptors, who prefer to carry their prey into a tree or onto a ledge to eat it, if possible), the strong grasping feet of (say) a great horned owl would actually be maladaptive.