On a lovely spring day, my wife and I were on our up into the Sierra Nevada foothills in central California for a weekend of camping. As we drove along a narrow road that traces its way up and down the crests and valleys of that part of the state, we were lucky enough to see something amazing! Just as we were coming around a beautiful curving stretch of forested road we saw movement off to our right. Up off the side of the road, two Turkey Vultures took flight. There was a deer carcass in the ditch that they had both been feeding on until they were disturbed by our passing car. One of the Turkey Vultures flew away from the road farther into the trees. The other decided to fly across the road, directly in front of our car! This startled us, and apparently did worse to the bird, because this is when the amazing thing happened. The Turkey Vulture threw up!
This is a behavior that many New World Vultures do, and may have several functions. One is called defensive vomiting and is used in predator deterrence. If a vulture feels threatened by a predator the vulture may vomit at, and onto, the predator coating it with smelly, partially digested carrion. I can imagine that being a very unpleasant experience for the predator, and causing it to want to leave as quickly as possible. Apparently many predators agree. A competing hypothesis is that the vulture’s vomit is actually a decoy. They give the predator something that it may want to eat, the vulture’s partially digested food, and while the predator is busy with that the vulture makes good its escape. In my reading, I have not found a lot of support for this hypothesis, but it is out there and has not been well investigated. A third reason that vultures vomit is to become lighter. Vultures are somewhat boom-and-bust feeders in that they cannot count on finding a carcass every day. This means that when they do find one, they eat a lot so that they have energy to see them through until the next carcass is found. The down side of eating a lot of meat is that it is heavy which makes a fast take-off rather difficult. If a full vulture is startled, and needs to get off the ground and up into the air and out of reach quickly, one fast way to lighten the load is to empty their stomach! This is exactly what I think the vulture we saw was doing. On suddenly finding itself in front of our oncoming car, and wanting to gain altitude as fast as it could, it threw up the deer meat it had just eaten, and thereby made itself lighter, and up it went. Actually quite ingenious!
What made me especially excited about this whole thing was that I had never actually seen this behavior before! I had read about it and heard other people talk about, but I had never witnessed it myself! I felt so lucky. It was one of the high points of my day!
Aaron N.K. Haiman has been a student of nature, and particularly of birds, since he was a small child growing up in Berkeley, California. After studying birds in college and graduate school, he now lives in West Sacramento, California with his wife and young daughter where he works for the State of California as an Environmental Scientist at the Sacramento-San Joaquin Delta Conservancy. Follow Aaron and read more of his writing by visiting his blog: A Birding Naturalist.
Photo by Michael Lane