Science News - February 25, 2012

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Pleased
to eat you
Wildlife surveys
of the Florida
Everglades in the
1990s found abun-
dant deer, raccoon
and opossums.
But those species,
and several others,
have plummeted
as the population
of introduced Bur-
mese pythons has
increased in recent
years.

3.0

Everglades National Park mammal abundances

Number observed per 100 kilometers driven

2. 5

2.0

1. 5

1.0

0.5

1996–1997 2003–2011

0.0

Deer
Raccoon
Opossu m s
Rabbits
Rodents
Foxes
S q uirrels
SOURCE: DORCAS ET AL/PNAS 2012

B obcats

common mammals, although sightings of each were down by more than 98 percent in the most recent survey. Counts were 94 percent lower for white-tailed deer, and bobcat sightings were down by 87 percent. And in contrast to the earlier survey, scientists saw no rabbits or foxes. Rabbits had been among the most common mammals seen in the 1990s.

Roadside sightings of mammal species remained unchanged between the two periods in areas outside the python range. In spots of recent python migration, mammal sightings were also down somewhat from a decade earlier, drops ranging from 20 to 80 percent, Dorcas’ team reports online January 30 in the Proceedings of the National Academy of Sciences.

The diminished mammal counts in python territory “are pretty similar to what we found,” says Joshua Holbrook of Florida Atlantic University in Davie. A more circumscribed road-sampling survey he coauthored in 2010 in Florida Scientist turned up nine mammals over four nights: seven deer, an opossum and an unidentified small mammal. On five nights, he and his colleagues saw none. Meanwhile, beyond the pythons’ range in the nearby Corbett Wildlife Management Area, he and Thomas Chesnes of Palm Beach Atlantic University sighted 40 mammals over nine nights.

“This study paints a stark picture of the real damage that Burmese pythons are causing to native wildlife and the Florida economy,” says U.S. Interior Secretary Ken Salazar. His agency announced new rules on January 17 that will ban the importation and interstate transport of Burmese pythons, yellow anacondas and two other invasive constrictors sold in the pet trade. All have been found in Everglades National Park.

With so many invasive constrictors already breeding in South Florida, research is now focusing on ways to limit their spread and better understand the prey they threaten. Although Burmese pythons need freshwater to survive, a team of biologists with the U.S. Geological Survey led by Kristen Hart in its Davie, Fla., lab showed that the snakes can apparently derive much of their needed moisture from the tissue of prey animals.

The team’s experiments suggest that python hatchlings can’t survive more than two months with access to only saltwater. But a pair of hatchlings was still alive after 200 days with access to only brackish water. And a yearling snake with access to only saltwater survived seven months — holding open the prospect that these adept swim-mers could, if motivated, migrate long distances through seawater, the team reports in the Feb. 10 Journal of Experimental Marine Biology and Ecology. In fact, Burmese pythons have already been found eating endangered wood rats on Key Largo, off the mainland coast. s

2

Back Story | SNAKES IN THE GRASS In most of North America, a constrictor found slithering around in the wild is bound to be a lost or intentionally released pet. But in Florida, Burmese pythons have started expanding from the southernmost reaches of the Everglades (red dots indicate numbers of sightings). Researchers believe a breeder or dealer may have deliberately released a number of snakes in the remote location.