SNAKES ON A (COASTAL) PLAIN

Animals move around. It's what separates us from the minerals. When I was about five, the first sight record for a Cattle Egret (Bubulcus ibis) was established in my home state of Utah. When I left high school the species was still considered accidental, but within five years it had become a common breeder. Today the New World population of these birds, descended from African stragglers a century ago, inhabits relatively unexploited pastureland habitat from Alaska to Tierra del Fuego. Any year now, Nine-banded Armadillos (Dasypus novemcinctus) should cross into my state as well. In the past couple of decades, the lovely Eurasian Bluethroat (Luscinia svecica) has traversed the Bering Strait into Alaska and Yukon, as the West Indian Shiny Cowbird (Molothrus bonariensis) slipped up the Eastern Seaboard into New Brunswick. These pioneering events can be random, or can be precipitated by climatic, geological or ecological changes. The Pliocene formation of the Isthmus of Panama was one of the most profound occurrences in recent geological history, allowing the migration of placental mammals into South America, and a sparser flow northward, which included those advancing armadillos.

These days, most pioneer species are assisted by humans, either exploiting anthropogenically altered habitat or actually being transported, either purposely or inadvertently. Peninsular Florida's subtropical climate provides the most welcoming habitat in the contiguous U.S., and a wide array of recent animal and plant species have set up shop there in the past century, including some 47 reptiles. Florida's most common reptile, the Brown Anole (Anolis sagrei) is a recent stowaway from Cuba, but lately all eyes have been on the big constrictors. Boa Constictors (Boa constricor) have reproduced in the Everglades for some 40 years, but are not known to breed elsewhere in the state (since they bear live young, it's a bit harder to confirm these things). Green Anacondas (Eunectes murinus) and Yellow Anacondas (E. notaeus) have been found in southern Florida, as have Reticulated Pythons (Python reticulatus-above), with no confirmed breeders from these three species. The fifth pioneer constrictor, the Burmese Python (P. molurus bivittatus), has so far been the only constrictor to really establish itself, a feat accomplished within the past six years. The first nesting Burmese was found in 2006, but it's likely that a thousand or more eggs had been laid in Florida by that time. The graph below shows the number of individual Burmese Pythons removed from Everglades National Park over the past fifteen years (data from last year are not yet available; the only released figure so far is “over 300”). In each of the past few years, increased effort has gone into removing pythons, probably exaggerating the curve's steepness some. It's much harder to estimate the species' total population with any accuracy than it is to assume they're there to stay.
Last week, Senator Bill Nelson of Florida introduced a bill intended to address this situation. The degree of sound biological advice he received can be inferred from the bill's title alone: A bill to amend title 18, United States Code, to include constrictor snakes of the species Python genera as an injurious animal. Should the bill pass muster, it would (despite the awkward phrasing) prohibit the interstate transport of Python spp. within the United States. Nelson's introductory comments were typically hyperbolic, particularly his contention that “...recently, researchers also found cougar parts in the stomachs of captured pythons. This development could signal a new threat to the endangered Florida panther, which we have been working so hard to save,” referring to an incident in November, 2005, when a Bobcat (Lynx rufus) foot was found in the lower GI tract of a female Burmese. This is just the latest in a string of hysteria, including a couple of fairly crazy USGS projections predicting python migrations into the American heartland (see below). These papers have been nicely debunked here and here.Nutty discussions about a problem, though, don't necessarily invalidate concern, and pythons in South Florida are something to be concerned about. Last year, the state initiated new regulations defining Burmese, Reticulated and African Rock Pythons (P. sebae), Green Anacondas, Amethystine Pythons (Morelia amethistina) and Nile Monitors (Varanus niloticus) as “reptiles of concern,” mandating implanted microchips in all captives over 2” in diameter and a $100 annual permit to own one. Legislators, wildlife managers and journalists have generally worked under the assumption that the wild pythons are descended from intentionally released, unwanted captives, but there is no evidence to support this. It is at least as likely that their release was a single unintended consequence of 1992's Hurricane Andrew. Whatever the case, the new state legislation is sound. The release of any exotic wildlife in Florida is a first degree misdemeanor, punishable by up to a year in prison and a $1,000. fine. Further dissemination of this fact and a bit of education for prospective snake-owners would go a long way here, especially at the pet shop end. Putting the practice of importing young, wild-caught pythons from Asia out of its misery would be a welcome blow against a destructive industry, in addition to driving the price of captive snakes out of reach of the less-than-serious keeper.

Florida Panthers (Puma concolor coryi) surely have bigger worries than pythons, and I consider the widespread agonizing over possible competition with Indigo Snakes (Drymarchon corais) to be overboard as well, due largely to the widely divergent optimum body temperatures of the two genera. The endangered Key Largo Woodrat (Neotoma floridana smalli) is another story. Perhaps the biggest concern of all is the potential spread of Reticulated Pythons further south into the Caribbean. This species swims well and has dispersed itself throughout Indonesia and the Philippines. In the simple ecology of the Caribbean islands, these snakes could wreak far more serious havoc than is likely in the complex Everglades community, where wildlife managers are busy trapping them, tracking them with dogs, and following radio-telemetered males to females. Because pythons and other poikilothermic predators do not feed regularly, a parcel of land can support far more individuals than it could a similar homeothermic species, and the maintenance of a python population at a somewhat innocuous level is feasible, if labor-intensive.
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upper: RETICULATED PYTHON & MASKED FINFOOT (1999) acrylic 20" x 30"
middle: Graph based on USNPS data. 2008 data added by CPBvK
lower: Map by USGS