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and center: Two pools that have dried to only a bit of mud and water, stranding
hundreds of fish, tadpoles, and crayfish. Fish include several species of
sunfish, catfish, killifish and mosquitofish, pickerels, and bowfin. Many
snakes feeding in drying pools muddy them up with their activity, feeding mainly
by feel on the concentrated prey, then bring
their prey back to shore to swallow them.
Most pitvipers are primarily ambush predators. Watching one forage, if you are fortunate enough to do so, consists of observing a snake sitting alertly, without so much as blinking an eye, for hours (or days) on end. Cottonmouths, on the other hand, can be very active foragers, though to our eyes, sometimes remarkably inept. One of their typical behaviors while foraging along pond edges or in shallow water is the “craning-cruising” posture, where they slowly crawl with the head and neck held a couple of inches above the ground or water surface. We have seen a couple of fairly different approaches to foraging in drying flatwood pools that are related to the stage of drying. While there is still ample water in the pools for the fish to be mobile, cottonmouths will submerge their heads and wave them around under water to locate and catch fish. Capturing a fish is probably mostly tactile; the pools are often so clouded with mud from the activity of hundreds of fish that seeing anything under water would be impossible. This type of tactile foraging is probably only feasible when the prey are extremely concentrated, as they are in drying pools. Aquatic foraging is not particularly well-suited to typical pitviper behavior; striking and releasing the prey, then scent-tracking it several minutes later as most pitvipers do, is not very practical when the struck prey can swim away. Instead, cottonmouths simply grab and swallow smaller fish without envenomating them. They do strike and release larger fish on occasion, but probably frequently lose them. On some occasions, we have seen fish in small pools become alarmed by the foraging gyrations of the cottonmouth and jump completely out of the water. Barbara Savitzky has extensively studied the foraging behavior of cottonmouths in laboratory arenas simulating natural environments, and found they spend far more time foraging along the edge of aquatic habitats than in open water (Savitzky 1992). She also found that cottonmouths usually bring fish caught in the water to shore to manipulate and swallow them, but that they occasionally lose them while positioning the fish for swallowing.
Cottonmouths feeding on dead or dying prey trapped in dried or drying mud often have their choice of prey items. This one is digging out a tadpole that is nearing the frog stage. Gaping before and after eating is often seen.
Even more fascinating than their aquatic foraging behavior, though, is their behavior at pools that have recently dried to mud holes. In these situations, fish and tadpoles will bury into the mud, and can live for hours, or perhaps even days, after the standing water is gone. The cottonmouths locate the lowest point in the former pond or depression, and concentrate their efforts where the prey are most abundant. They slowly and methodically dig their snout into the mud and pull out their prey individually. Once extracted, though, the fun has just begun. Contrary to the observations of other researchers (Savitzky 1992), the snakes do not always hold on to the prey in these situations. We have observed on numerous occasions that a few flops or wiggles from a tadpole weighing less than 20 g will cause a cottonmouth weighing more than 200 g to release it. Once released, they seem to have a hard time relocating them, and when they do, it seems to be primarily by olfaction, accompanied by lots of tongue-flicking and head-waving. Though the tadpole may be flopping on the mud an inch or two from the snake’s head, cottonmouths don’t seem to orient to the prey visually. They will sometimes give up on a dropped prey item, and go back to the mud and dig out a new one. Perhaps when prey are abundant and easily replaced, cottonmouths will drop those that are capable of inflicting damage (as from the pectoral spines of a small catfish) or those that resemble dangerous prey (tadpoles).
When feeding in mostly dried mud, digging the prey (often still living) out can be a chore. The eyes of these snakes are sometimes so covered with dried mud that it's hard to imagine they can see what they are doing very well.
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