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on immobile prey (or carrion) in the mud has another advantage - the
cottonmouths often have several different prey sizes and types from which to
choose. The snake on the right is surrounded by small Gambusia, but seems to be
looking for something bigger.
Another interesting aspect of these feeding behaviors is the choice of available pools used by the foraging cottonmouths. Since the pools in these habitats range in size from small depressions a few feet across and a couple of inches deep to some, mostly manmade, that are dozens of feet across and several feet deep, pools that are at a stage of drying where prey are highly concentrated can be present for a couple of months in a row. Obviously, there are also permanent ponds or lakes in the vicinity to act as refuges for fish populations during extended droughts. The behaviors and population dynamics of the fish that are involved in these repeated local extinction and recolonization events during flood/drought cycles are nearly as interesting as the behaviors of the snakes (but not quite!). As expected, snakes tend to avoid the larger, well-filled pools until later in the season when shallower pools have completely dried. There are probably other factors involved in pool selection, though; for example, we don’t see cottonmouths foraging in the same pools that wading birds are using. Not surprising, given that some of the wading birds (such as wood storks and the larger herons and egrets) using these resources are known to prey on cottonmouths as well. Alligators, usually juveniles up to a couple of feet long, also take up temporary residence in the pools, and are also a potential predator for smaller snakes. The presence of other cottonmouths in a pool may also influence foraging decisions. When more than one snake is present in a single pool, they are usually snakes that are nearly equal in size, or a large adult paired with a juvenile snake of much smaller size. Other observers have suggested the formation of dominance hierarchies among individual cottonmouths foraging together (Ernst 1992). Since cottonmouths will engage in cannibalism, one might expect that smaller individuals in the mixed-size pairs would be quite wary of their larger brethren, but it may be that under these conditions of prey abundance, cannibalism is not a real concern.
In addition to
cottonmouths, several other species of aquatic snakes also take advantage of
these resource bonanzas, including several species of water snakes (Nerodia) and
crayfish snakes (Regina).
Observing the behavior of these magnificent snakes is not too difficult; they can be amazingly abundant in the flatwoods. We have found as many as 40 in a couple of hours. They can be approached closely if one is reasonably careful to avoid rapid movements or heavy vibrations. When foraging in the smaller muddy pools and mud holes, their eyecaps are often covered with mud, so their ability to see approaching humans is probably impaired (this may also account for their apparent inability to visually track lost prey described earlier). Fortunately, they can be observed throughout the day if the temperature is appropriate. Until about May, they will forage throughout the day on cooler days, or concentrate their foraging in morning and late afternoon as temperatures rise. As typical summer temperatures approach, they seem to become mostly nocturnal in their behavior. We also see a variety of other snakes using these drying pools, including a couple of species of water snakes (Nerodea fasciata and floridana), ribbon snakes (Thamnophis sauritus), and glossy crayfish snakes (Regina rigida).
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