Feral species challenge understanding of predator/prey relationships
MIAMI––Florida hosts 1.3 million alligators, about a quarter of a million pit bulls, a few billion mosquitoes, and––according to promotional material for the 2016 Python Challenge Burmese Python Removal Competition––perhaps 100,000 pythons, the species officially deemed most in need of killing after the first Florida bear hunt in 21 years ended in October 2015.
Serious population modeling suggests that the actual Florida python population is probably more like 10,000, but the Florida Fish & Wildlife Commission tends to pass lightly over numbers, having sold 3,700 licenses to shoot the estimated 3,300 black bears in the state. After 304 bears were actually shot, including 36 lactating sows, the FWC speculated that Florida might actually have 5,000 bears.
The Python Challenge will be underway from January 16, 2016 through Valentine’s Day.
“So far, more than 500 competitors have signed up,” reported Jenny Staletovich of the Miami Herald, “about a third of the number who participated in the inaugural Challenge in 2013. That hunt drew global attention but disappointed hunters with a haul of just 68 snakes.”
Despite the low bag in 2013, the python challenge hosts, the Florida Fish & Wildlife Conservation Commission and the Fish & Wildlife Foundation of Florida, appear to regard pythons as the state’s most urgent environmental health and safety threat.
Less deadly than armadillos
Certainly no effort appears to have been spared to portray pythons as a fierce alien invader worthy of trophy hunters’ attention. In addition to the flurry of media releases and training events accompanying the opening of any hunting season, the Python Challenge promo included an “Invasive Species Awareness Festival” and two online contests.
But among the alligators, pit bulls, pythons, other predators, and other alleged invasive species roaming Florida, pythons rate well behind even armadillos: 10 Floridians contracted leprosy in 2015 from killing and eating armadillos, according to Florida Department of Health data.
The body count
As the 2016 Python Challenge started, Florida alligators had most recently killed a person on November 13, 2015: burglary suspect Matthew Riggins, 22, believed to have hidden in a lake near Barefoot Bay to evade law enforcement. His remains were recovered 10 days later.
Pit bulls had killed three people in 18 months in Miami-Dade County alone, where pit bulls have been banned since 1989, yet Miami-Dade Animal Services on January 13, 2016 boasted that it had “successfully reached its goal, achieving a combined save rate for cats and dogs of 90% in 2015.” The Miami-Dade pit bull victims included Nyjah Espionsa, almost age 2, on December 20, 2015; Carmen Reigada, 91, on September 22, 2015; and Javon Dade Jr., age 4, on August 13, 2014. (See Christmas baby killed by pit bulls because Miami-Dade law is not enforced.)
Florida bears have injured 16 people since 1976, according to Florida Fish & Wildlife Conservation Commission data. A bear killed a Yorkshire terrier in an accidental encounter near Orlando just three weeks before the 2015 Florida bear season opened.
Wild pythons have yet to kill or seriously injure anyone, either in Florida or anywhere in North America.
Victim put python on shoulders
Worldwide, the last python known to have killed anyone was captured on December 27, 2013 by security guard Ambar Arianto Mulyo, 59, near the Bali Hyatt hotel in Sanur, Bali, Indonesia.
Reported Bali Hyatt hotel security manager Agung Bawa, who witnessed the incident, “Mulyo managed to secure the snake’s head and tail and put it on his shoulders, but the python wrapped itself around his body and strangled him.”
Facebook images circulated a few weeks earlier of a python allegedly swallowing a drunk near Attapadi, Kerala state, India, turned out to have been faked. Globally, since 1900, there appear to be only 11 authenticated cases of wild Burmese pythons actually killing people: seven in the Philippines, two in Indonesia, one each in Malaysia and Burma.
2009 Florida death
Pet pythons have been considerably more dangerous, killing at least half a dozen Americans and Canadians since 1992. Most notoriously, an escaped pet African rock python killed brothers Noah and Connor Barthe, ages four and six, on the night of August 5, 2013 in Cambelltown, New Brunswick, Canada.
An escaped pet albino Burmese python killed 2-year-old Shaiunna Rose Hare in her crib on July 1, 2009 in Sumter County, Florida. Her parents, Charles Darnell and Jaren Hare, were convicted in 2011 of third degree murder and child neglect.
“Although that Burmese python was the instrument of death, those two defendants are responsible for the death of Shaiunna Hare,” summarized the prosecution. The python had not been fed for a month, had last been fed a roadkilled squirrel, was confined in a terrarium only by a quilt thrown over the top, and had escaped five times in the month preceding the two-year-old’s death.
Nonetheless, the fact that the “instrument of death” was a python seems to have made the most lasting impression on Floridians.
Five pythons struck at biologists
“The estimated tens of thousands of Burmese pythons now populating the Everglades present a low risk to people in Everglades National Park,” the U.S. Geological Survey and National Park Service scientists agreed in a February 27, 2014 media release. “The human risk assessment looked at five incidents that involved humans and Burmese pythons over a 10-year period in Everglades National Park. All five incidents involved pythons striking at biologists who were conducting research in flooded wetlands.”
Were the biologists, like Agung Bawa in Bali, menacing the pythons?
Humans not on menu
“The strikes did not appear to be defensive, but were more likely were associated with aborted feeding behavior,” said U.S. Geological Survey wildlife biologist and herpetologist Bob Reed, who led the assessment.
“In four of five cases the python was small compared to the size of the person, which resulted in the snake likely aborting the attack upon realizing the large size of its prey,” concluded Reed and co-author Skip Snow, a retired Everglades National Park scientist.
In other words, even when the pythons had the drop on the humans, humans were not on their menu.
What are they eating?
So if Florida pythons are not eating people, what are they eating?
Allegations that pythons might be eating even the alligators out of house and home gained momentum in 2010 after Proceedings of the National Academy of Sciences published findings by Davidson University biology professor Michael Dorcas that according to roadkill surveys done in the Everglades from 1993 to 1999, and nighttime road wildlife surveys done between 2003 and 2011, there had been declines of 99.3% in the frequency of raccoon observations, 98.9% in the frequency of opossum observations, and 87.5% decrease in the frequency of bobcat observations. Rabbits appeared to have vanished entirely.
Summarized Bryan Walsh of Time magazine, “Since all of those animals can serve as a python’s dinner––and given the fact that the mammals were more common in areas where the pythons hadn’t been seen––it’s reasonable to infer that the Burmese pythons are treating the Everglades as an all-you-can-eat buffet.”
That was the uncritical spin that Dorcas, Walsh, and most other media gave to the data. But overlooked was that raccoons, opossums, bobcats, and rabbits are also prey of American alligators.
Dorcas’ earliest data came from a time when the Florida alligator population was officially estimated to be just under one million. Alligator hunting had just been reopened in 1987, after a 20-year hiatus due to too few alligators.
By 2009 the Florida alligator population was officially estimated to be 1,850,000, twice what it was in the early 1990s.
100 gators per python
A January 2010 cold snap knocked alligator numbers down to the present estimated 1.3 million, where the population appears to have stabilized, perhaps at least in part by predation pressure from pythons. Whatever the reason, though, alligators still outnumber pythons in the Everglades by a minimum of at least a dozen to one, and most likely––discounting the claim of 100,000 pythons as hyperbole––by more than 100 to one.
Allegedly reinforcing the Dorcas study was the fate of 26 rabbits who were trapped in storm water treatment areas outside Everglades National Park, radio-collared, and released into the park in September 2012. Seventeen of the rabbits were killed by pythons, reported University of Florida biologist Robert McCleery.
Noted Jennifer Kay of Associated Press, “The prey consumed by the 68 snakes caught in the 2013 hunt was almost evenly split between small mammals, such as cotton rats and rabbits, and wading birds. A few also made room for alligators.”
But an obvious limitation of the Dorcas, McCleery, and 2013 Python Challenge data was that it all came from the relatively high and dry parts of the Everglades easily accessed by road, not from the much wetter designated wilderness regions constituting 86% of the habitat.
While relatively few alligators were found among the prey of pythons killed near roadsides, there is no python habitat in Florida that is not also alligator habitat, and does not have alligators in sufficient abundance to support routine python predation.
Predators of crocodilians
More significantly, pythons and other giant constricting snakes evolved, long before mammals existed, as predators of crocodilians, the order including American alligators. Indeed, the largest constricting snake in the fossil record, the 42-foot Titanoboa, and a 20-foot croc, both circa 60 million years old, were found more-or-less together in the Cerrejon open-pit coal mine in Colombia.
Until the arrival of pythons a few decades ago, Florida––the northernmost habitat for any crocodilians––was the only part of the world with abundant crocodilians but no giant constricting snakes to prey upon them since the last Ice Age covered Florida circa 18 million years ago.
“Death roll” helps constrictors
The constricting method of killing used by pythons and anacondas takes advantage of the “death roll” used by crocodilians to drown prey and fend off attackers.
Mammals and birds are secondary prey for pythons, who may grab whatever is easily accessible, but often do not bother with warm-blooded species, especially if those species are large or quick.
U.S. Geological Survey research has established that Florida python home ranges are on average an area of about three miles square, mostly in saltwater slough and coastal habitats featuring tree islands, where a python can lie in ambush to drop down on unwary prey.
Florida python prey includes some deer and feral pigs, but alligators appear to be the most abundant and most often accessible large prey species.
Brake on feral rock pythons?
The Burmese pythons constituting most of the Florida python population may also hunt feral northern African rock pythons, a somewhat smaller and less aquatic feral species that was considered an incipient threat to the Everglades circa 2000, but is now seldom seen. Twenty-nine rock pythons were captured between 2001 and 2011 in a six-square-mile suburban area west of Miami, one killed a dog in 2013, and one was hit by a vehicle removing roadside vegetation in 2014.
Rock pythons have so far not been able to extend their range into Burmese python range, despite a March 2015 U.S. Fish & Wildlife Service pronouncement that “Scientists have not found any way of eradicating invasive constrictor snakes once they become established in the wild.”