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Bay State Forest, where we made most of our cottonmouth observations, changed
dramatically in the summer of 1998 during the catastrophic wildfires that
ravaged much of Florida. Prior to that summer, most of the habitat was
closed canopy flatwoods; probably half or more of the flatwoods burned during
those fires. Conditions in the post-fire habitats are significantly better
for some organisms (like wildflowers), but it's not clear how the fires (and
subsequent logging and salvage operations) affected the cottonmouth populations.
Cottonmouths, like other snakes adapted to eating large meals relative to their own body size, are admirably adapted to alternating periods of scarcity and abundance. They can not only consume a quantity of prey equal to their own body weight in a short period of time, but can also make resources stored during their periods of gluttony last for an exceedingly long time. All snakes allow their body temperature to drop when environmental temperatures do, or seek cooler microhabitats when conserving resources. Lower body temperature results in a decreased metabolic rate (energy consumption), and this alone allows some snakes to fast for months (or even years in extreme cases) at a time. Their frugality with stored energy goes beyond this, though. Studies by physiologists Steven Secor and Jared Diamond have shown that some snakes, including rattlesnakes and pythons, conserve energy in other ways beyond thermoregulation. Some snakes that feed infrequently and on large meals essentially turn their gut tissues off when in a non-feeding state. This means that they allow the cells lining their gut to atrophy, stop producing enzymes, and wait until food is present in the gut before becoming active again. During this period of “upregulation” or “gut refurbishing”, resting metabolic rates can skyrocket to seven times as great as they were previous to feeding (Secor et al. 1994; Secor and Diamond 1995). This remarkable discovery has numerous implications for snake biology, and it is of great interest to know how many species shut down the gut between meals. Certainly it would be expected in species like cottonmouths that often live under extremely variable conditions of resource availability.
Though not really aggressive, the somewhat combative responses of cottonmouths when threatened probably add to their mortality rate. In the middle is a gravid cottonmouth that was killed by cretins. We opened her abdominal cavity to see how far along the embryos were. Large yolk masses give some idea of how much energy these females expend during reproduction. Unfortunately, finding dead cottonmouths (and other snakes) is still far too common in Florida, even in protected areas and refuges. In many cases, the morons killing the snakes probably don't even know which species they are persecuting.
Cottonmouths in other areas experience resource fluctuations similar to or greater than those we see in our flatwoods snakes. Charles Wharton studied the dense cottonmouth populations that occur on Seahorse Key and several other small islands in the Gulf of Mexico (not the Florida Keys!!), and found that in those areas, their main food source was from rookeries of nesting birds in spring and summer (Carr 1992; Wharton 1966, 1969). The snakes congregated under the nesting areas, and ate fish dropped by parent birds feeding their young, or baby birds that dropped out of the nests. Wharton kept track of the weights of individual snakes in these populations, and found that most individuals steadily lost weight all year long, until the bird nesting season began and food began to fall from the sky! For the Gulf cottonmouths and our flatwood cottonmouths, this resource boom couldn’t come at a better time. Pregnant cottonmouths begin to contribute yolk to their developing eggs in the spring, and give birth later in the summer. The burst of food during the spring or early summer feeding period may heavily influence the number and size of their offspring that are borne live later in the year.
Our observation of flatwoods cottonmouth behavior has been fairly casual, and has largely been an enjoyable diversion from our taxing and exhausting studies of pigmy rattlesnakes (May et al. 1997). However, this remarkable ophidian spectacle begs for more serious and intensive study. For example, what are the movement patterns of individual snakes as smaller ponds dry and fish become concentrated in the larger remaining pools? Do cottonmouths engage in extensive migrations to track this sequence of drying pools, or do they gorge themselves at their nearest pool and then retreat to cover until the next feeding period? What are the behavioral interactions between individual snakes sharing the same pool? How do wet years, when pools fail to dry up and concentrate resources for the snakes, affect growth and reproduction of the cottonmouths? For serious students of snake biology and behavior, these populations and behaviors present a remarkable opportunity for further discovery.
Carr, Archie. 1994. The Gulf Island Cottonmouths. pp. 225-229 in A Naturalist in Florida: a celebration of Eden. Yale University Press, New Haven.
Ernst, C.H. 1992. Venomous Reptiles of North America. Smithsonian Institution Press, Washington.
May, P.G., S.T. Heulett, T.M. Farrell and M.A. Pilgrim. 1997. Live fast, love hard, & die young: the ecology of pigmy rattlesnakes. Reptile & Amphibian Magazine 45: 36-50.
Savitzky, B.C. 1992. Laboratory studies on piscivory in an opportunistic pitviper, the cottonmouth, Agkistrodon piscivorus. pp. 347-368 in Campbell, J.A. and E.D. Brodie, Jr., eds., Biology of the Pitvipers. Selva Press, Tyler, Texas.
Secor, S.M., E.D. Stein and J. Diamond 1994. Rapid upregulation of snake intestine in response to feeding: a new model of intestinal adaptation. American Journal of Physiology 266: G695-G705.
Secor, S.M. and J. Diamond. 1995. Adaptive responses to feeding in Burmese pythons: pay before pumping. The Journal of Experimental Biology 198: 1313-1325.
Wharton, C. H. 1966. Reproduction and growth in the cottonmouths, Agkistrodon piscivorus Lacepede, of Cedar Keys, Florida. Copeia 1966: 149-161.
Wharton, C.H. 1969. The cottonmouth moccasin on Sea Horse Key, Florida. Bulletin of the Florida State Museum Biological Science. 14: 227-272.
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