Peter G. May and Terence M. Farrell
Stetson University, DeLand FL 32720
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This article originally appeared in Reptile & Amphibian Magazine, 1998, 56: 18-24.
Florida Cottonmouths (Agkistrodon piscivorus conanti): These snakes can be abundant in the right time and place. The snakes on the right are showing different degrees of the open-mouth gape used as a threat, from which they acquired the common name.
Snakes, like other ectotherms, have a huge advantage over endotherms in environments that are highly variable over time. Regardless of the source of variability, the ability of ectotherms to vary their body temperature, coupled with their lower rate of energy expenditure than a similarly sized endotherm at the same body temperature, allows them to wait out the bad times using stored resources. During good times, the prodigious feeding capacity of snakes allows rapid accumulation of fat reserves that will be used to wait out the next bad spell. Highly variable environments often bring to mind temperate habitats at higher latitudes, where climatic conditions are unfavorable for most organisms for much of the year. The tropics and more southerly areas, on the other hand, are often thought of as being relatively invariant and benign to the organisms that occur there. For some organisms in habitats of tropical and near-tropical areas, though, environmental conditions can vary tremendously over the course of a year. The pine flatwoods habitats of Florida are such an environment, and the cottonmouths that are often abundant in these areas are highly adapted to a boom-and-bust lifestyle.
Young cottonmouths (left) are more boldly colored
than adults, and have a yellow tail tip used to lure prey. Adults can be dark
and show little banding, or can retain prominent patterning (right).
The cottonmouth (Agkistrodon piscivorus) is a well-known and widely mythologized pitviper that ranges in the eastern U.S. from southern Virginia all the way to the Florida keys. The mythology surrounding the cottonmouth is responsible for the death of countless harmless colubrid snakes that are aquatic or semi-aquatic in habit; in most of the cottonmouth’s range (and often out of its range), any snake seen within 100 meters of water is labeled a cottonmouth or water moccasin and promptly dispatched by ophidiophobes. While the cottonmouth merits respect because of its capacity for inflicting damage through its bite, it is equally impressive from a purely biological perspective. Occasionally obscenely abundant in appropriate habitats (see Carr 1992 for a classic account), the cottonmouth is the only pitviper that is adapted for a primarily aquatic or semi-aquatic existence. In some of the habitats favored by cottonmouths, the presence of available prey, or even standing water, can be a highly seasonal event. In the past couple of years, we have become avid students of cottonmouth feeding behavior in the pine flatwoods of central Florida.
habitats in the flatwoods of central Florida consist of both natural and
man-made low areas that fill with water during the wet season, then often dry
out by late winter-early spring. The left and middle shots show the same
pool about four weeks apart.
Pine flatwoods are one of the most widespread terrestrial ecosystems in Florida. They occur as broad bands of habitat that were once shallow marine seas. Their geological history has endowed them with soils that are nutrient-poor and often characterized by a layer of clay several feet deep (the hardpan layer) that prevents the infiltration of water to the underlying aquifer. Consequently they are slow to drain when flooded, and may be mostly inundated by inches to feet of water for weeks at a time. Especially during Florida’s rainy season (usually May-September) they become saturated and flooded. During dry periods (typically from November-April), they drain and often become bone-dry before seasonal rains return. It is during these drying periods that a remarkable biological event occurs - congregation of cottonmouths (and other predators) at the shrinking water holes to gorge themselves on the concentrated and helpless aquatic vertebrates. Snakes as a group are often difficult to study behaviorally in the field - they are often cryptic, very aware of potential predators, and generally hard to find and observe. For most snake enthusiasts, the vast majority of snake observations are of a very specific group of behaviors - escape and/or defensive behaviors. Flatwoods cottonmouths can be a notable and welcome exception.
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