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Alternate title suggested by David Steen: Why snakes might benefit from holding it
|A young Racer (Coluber constrictor) that has eaten a|
Ring-necked Snake (Diadophis punctatus) nearly 92% its length
|And the python's small heart grew two sizes that day|
Figure from Riquelme et al. 2011
|Uromacer oxyrhynchus just can't hold it's poop|
|A Burmese Python intestine before (top), two days|
after (middle), and 10 days after (bottom) eating.
From Secor 2008
|Poop from this African Rock Python's last meal might help anchor it|
as it laboriously swallows this wildebeest
In addition to providing ballast, the long time the fecal material spends inside the intestine could potentially increase the absorption of nutrients and water, although it probably doesn't take many months before the snake has got all it can out of its old meals. Uric acid and feces are normally mixed in snakes with short passage times, but in heavy-bodied viperids, boids, and pythons, feces are usually more compact and are more separate from the uric acid.
Few people have looked very deeply into these patterns of defecation (perhaps few would want to), so a lot of questions remain: does more frequent activity induce premature defecation? Do drinking or skin shedding influence defecation patterns? Do these patterns hold up in the field? What other functions might snake poop have? One study showed that captive snakes pooped more quickly after their cages were cleaned, whereas control animals whose cages were merely rearranged did not, which suggests that snakes might be using their feces for marking...something (we really don't know what since they aren't generally thought of as territorial, although they are a whole lot more social than most give them credit for). The mysteries are many.
Chiszar, D., S. Wellborn, M. A. Wand, K. M. Scudder, and H. M. Smith. 1980. Investigatory behavior in snakes, II: Cage cleaning and the induction of defecation in snakes. Animal Learning & Behavior 8:505-510 <link>
Cundall, D. 2002. Envenomation strategies, head form, and feeding ecology in vipers. Pages 149-162 in G. W. Schuett, M. Höggren, M. E. Douglas, and H. W. Greene, editors. Biology of the Vipers. Eagle Mountain Publishers, Eagle Mountain, UT <link>