by Whit Gibbons

March 17, 2013

Until last month, I had never seen a puff adder. After two days in South Africa, I had seen nine. Although this highly venomous viper is shy if unprovoked, the species is credited with the majority of human deaths from snakes on the African continent. Apparently some folks have a way of provoking them.

Mike Dorcas, a professor at Davidson College, and I went to South Africa to collaborate with colleagues conducting research on vipers and cobras. Our hosts were Graham Alexander, a professor at Wits University in Johannesburg, and Xavier Glaudas, who has a postdoctoral position. Xavier was one of my students at the University of Georgia, conducting studies on pit vipers - rattlesnakes, cottonmouths and copperheads. He now works with the even more dangerous puff adder.

Puff adders reach lengths well over five feet, and the largest ones have a mid-body diameter approaching that of a football. The head of the largest one we found was about as wide as my boot.

Puff adders are typically very secretive and well camouflaged, so hunting for them is not as easy as it sounds. The reason we found several is because most of them had radio transmitters in them that allowed us to locate them in the wild. They had been caught over the previous month, and the researchers had surgically implanted a transmitter in each one before releasing it. Xavier is then able to track the snakes' movements on a daily basis.

Xavier's project is the first of its kind in Africa. One scientific goal is to determine how a male puff adder's feeding intake affects reproduction. The specific research objectives are to find out if well-fed male puff adders cover more ground in search of receptive females, and if they win more battles for access to females against other not-so-well-fed males. Prior to mating, male puff adders, like most pit vipers in North America, often engage in combat to see which one gets the female. They don't bite each other. The contest consists of each snake trying to physically overpower the other in what looks like an arm wrestling contest (with really big arms; for their length, puff adders are one of the stoutest large snakes). Presumably snakes that have consumed more prey than others will be healthier and heavier. They will also presumably travel longer distances to find females and will win more contests. But no one knows for sure. The experiment will help scientists better understand whether enhanced feeding opportunities can decide which male is more effective at acquiring females.

A puff adder will eat almost any vertebrate that crosses its path, mostly small mammals, birds, and lizards. I watched with trepidation as Xavier offered a native mouse to one of his animals as it lay motionless and virtually invisible beneath a bush. Leaning into the bush he used long tongs to dangle the already dead prey in front of the snake's mouth to entice it to eat. In the experiment, he feeds half of the male snakes mice but leaves the other half to fend for themselves in the natural environment. Such studies help unravel the endless mysteries about how wild animals interact with others of their species and what determines whether one individual is more successful than another.

Will the well-fed experimental puff adders be more successful in mating than their counterparts that are feeding at the normal rate? The results of the study will become clear later in the year during the reproductive season. Xavier is testing the hypothesis that a direct connection exists between having a few good meals and mating success.

Conducting field ecology experiments is a time-consuming process and, with puff adders, a risky enterprise. But uncovering details about how ecological systems work is the way we increase our understanding of the natural world. I was captivated watching these incredibly dangerous yet highly camouflaged snakes up close in their native habitat. I was also glad Xavier was the one feeding them the mice.

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