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Burmese pythons (Python molurus bivittatus) are native to Southeast Asia, but toward the end of the 20th century, they established themselves as a breeding population in the U.S. state of Florida, specifically in the Everglades. A popular exotic animal that has been released or has escaped from people's homes or outdoor enclosures, the first of these snakes was observed in Everglades National Park in 1979. Because they are well adapted to thrive in the South Florida environment they are considered as an invasive species. Between 2001 and 2005, more than 200 Burmese pythons were observed in park boundaries and National Park Service staff created a policy to remove and euthanize them immediately. The estimated population of pythons in the Everglades is between 5,000 and 180,000, and they can be found in all areas of Everglades National Park, Big Cypress National Preserve, and have been observed north of the parks' boundaries.
Burmese pythons eat amphibians, reptiles, birds, and mammals that vary in size from small rodents to deer. Spectacular photographs of the snakes in struggles with native alligators (Alligator mississippiensis) have been released, directing international attention on the problem of invasive species in the Everglades. Authorities have proposed curbing the import of several species of snakes into Florida. A scientific study regarding the impact of Burmese pythons in the Everglades, published in late 2011, asserts that populations of mid-size mammals such as raccoons (Procyon lotor), opossums (Didelphis virginiana), and rabbits (Sylvilagus), all native to South Florida, have declined as the number of Burmese pythons has increased. Burmese pythons were included on a list of four snakes banned from import into the U.S.; Secretary of the Interior Ken Salazar announced the ban at Everglades National Park in January 2012.
The Everglades is a region of subtropical wetlands comprising the lower third of the Florida peninsula, fed by a slow-moving river that empties from Lake Okeechobee into Florida Bay, about 60 miles (97 km) wide and 100 miles (160 km) long. During the 20th century, the population of Florida increased at four times the rate of the rest of the country, and much of the Everglades were drained for agriculture or otherwise altered for urban development. Many exotic plant species were introduced to improve landscaping and drainage, and animals were imported as food or pets. Only 25% of the original Everglades remains, protected within Everglades National Park. The subtropical climate of South Florida and the location of the Everglades, surrounded by the South Florida metropolitan area to the east, Naples to the west, and Florida Bay to the south, make it particularly vulnerable to infestations of exotic species. With more than 40 species, no other location in the world harbors as many exotic reptiles as Florida.
Burmese pythons are native to many parts of South Asia, Southeast Asia and southern regions of China. They are endangered in Southeast Asia, where they are hunted for their skins and captured for sale overseas as exotic pets. They can grow 18 feet (5.5 m) and weigh over 200 pounds (91 kg) and are thus one of the world's largest snakes. They have light brown skin and dark red or brown blotches outlined in black, although python breeders have created several variations of patterns and colors—including albinism—that have been observed in the wild. Capable of climbing trees and swimming, they can remain submerged for up to 30 minutes; they have successfully made the 6-mile (9.7 km) journey to Key Largo over Florida Bay, where they have been observed but are not yet established.
Burmese pythons in South Florida typically eat rodents, but can feed also on fish, amphibians, other reptiles, and birds. Animals ranging in size from wrens to white-tailed deer have been found in captured pythons' digestive tracts, as have other animals considered invasive to the Everglades, such as cats. As constrictors, Burmese pythons seize and wrap themselves around their prey, suffocating them, then proceed to consume them entirely. Their size is dependent upon how much they feed. They can live 15 to 25 years and can reproduce prodigiously: one female can have a clutch of 100 eggs. The hatchlings are larger than native snake hatchlings and grow more quickly when food is plentiful, thus they are less vulnerable to predation. The likely predators for pythons in the Everglades are alligators, American crocodiles, black bears, and cougars. Hatchlings are also likely vulnerable to hawks, Golden Eagles, raccoons, and bobcats.
A popular animal in the exotic pet trade, a Burmese python (as of 2005) could be purchased for as little as $20. The number of Burmese pythons imported in the U.S. jumped from 17,000 (1970–1995) to 99,000 between 1996 and 2006. The first Burmese python was observed in Everglades National Park in 1979, but no more were found until 1995. Between 2001 and 2005, however, the number of pythons observed by workers in water management or ecological restoration efforts or killed by farm machinery in and near Everglades National Park rose to 201, and doubled to 418 between 2006–2007, at which time a nest of eggs was also discovered, causing national park staff to determine that pythons had begun breeding in the wild. In 2009, the South Florida Water Management District estimated between 5,000 to 180,000 Burmese pythons were living in South Florida.
Despite the infestation being relatively recent, python predation is of particular ecological concern. Because of human action and habitat encroachment, several animals that are native to South Florida—or birds that regularly migrate to the Everglades—are threatened or endangered. Some of the same species have been observed in the gastrointestinal tract of Burmese pythons during necropsy. Although they have not become established on Key Largo, those found in the Keys have been observed eating the endangered Key Largo woodrat (Neotoma floridana smalli), and Burmese pythons are in direct competition with the native indigo snake (Drymarchon couperi), a federally threatened species. Although not observed as of 2008, authorities are concerned that other threatened or endangered species, such as the Florida panther (Puma concolor coryi), mangrove fox squirrel (Sciurus niger avicennia), Key Largo cotton mouse (Peromyscus gossypinus allapaticola), wood stork (Mycteria americana), Cape Sable seaside sparrow (Ammodramus maritimus mirabilis), and American crocodile (Crocodylus acutus) may also be targeted or otherwise adversely impacted by Burmese pythons, as the snakes may consume and thus limit the food resources for the mentioned animals.
A study published in December 2011 established that the number of mid-size mammals observable at evening and night along major roads in Everglades National Park had drastically decreased. The authors measured more than a 99% decrease in the number of raccoons, nearly 99% and 88% decrease for opossums, bobcats (Lynx rufus), and white-tailed deer (Odocoileus virginianus), and the authors were unable to observe any rabbits during their period of study. Other mammals, such as rodents, coyotes (Canis latrans), and Florida panthers were observed at a slight increase but still remained infrequent. The study's authors pointed to the Burmese python as responsible for the decreased numbers of mammals: the decreases began occurring about the same time Burmese pythons sightings increased, locations where pythons have been observed for the longest periods of time also shows severe decreases in numbers of mid-size mammals, and in other areas where pythons have been observed more recently, some mammal species numbers are lower than where no pythons have been observed. Raccoons, opossums, rabbits, deer, and bobcats live or feed near water where pythons tend to live, they have been found in digestive tracts of pythons, and as there are no snakes native to the Everglades near the size that Burmese pythons can grow, the study authors stated the mammals "may be naive to predation by large snakes". Everglades National Park is an ecological sanctuary where hunting is illegal; water levels that are often human-controlled, or other environmental factors, have remained unchanged over the past two decades.
In May 2013, a Florida man  captured and killed a Burmese python 18 feet, 8 inches long (5.7 meters) that weighed 128 lbs. It was the longest Burmese python ever caught in the Florida Everglades.
In response to the number of exotic reptiles released by pet owners who are no longer able to care for animals that grow beyond a manageable size, Florida enacted laws to prohibit the release of exotic animals into the wild. To dissuade people from dumping animals, local authorities have begun holding "Nonnative Amnesty Days" in several Florida locations where pet owners who are no longer willing or able to take care of non-traditional pets can deposit animals without being prosecuted for illegal dumping of exotic species. The Florida Fish and Wildlife Conservation Commission (FWC) initiated a task force to concentrate on identifying the most invasive animals. The agency created a list of "Reptiles of Concern" for the Burmese python, African rock python (Python sebae), amethystine python (Morelia amethistina), reticulated python (Python reticulatus), green anaconda (Eunectes murinus), and the Nile monitor (Varanus niloticus), all of which were chosen for their formidable sizes and aggressive natures. Florida also began requiring owners to pay a permit fee of $100 a year and place microchips on the animals. The FWC has furthermore allowed hunters permits to capture Reptiles of Concern in a specific hunting season in wildlife management areas, euthanize the animals immediately and sell the meat and hides.
One natural measure of control for Burmese pythons is extreme cold temperatures atypical for South Florida winters. For the first two weeks of January 2010, temperatures dropped below what had ever been recorded for several locations in South Florida. Monitoring stations recorded 48 °F (9 °C) in Miami and the next day temperatures ranging from 25–32 °F (−4–0 °C) from several urban South Florida locations. In addition, the cold was sustained over ten days—a period of time that also set records. This cold snap killed significant numbers of native animals, including West Indian manatees (Trichechus manatus), sea turtles (Chelonioidea), crocodiles, and numerous species of fishes. It also brought large number of deaths for exotic animals such as iguanas (Iguana iguana), and pythons.
To combat the number of exotic snakes in the U.S., and specifically in South Florida, the U.S. Department of the Interior added four species of snakes—Burmese pythons, two subspecies of African rock pythons (northern and southern), and the yellow anaconda (Eunectes notaeus)—to Lacey Act provisions, making their import into the U.S. illegal, in 2012. U.S. Secretary of the Interior Ken Salazar announced the inclusion of these species at Everglades National Park.
On January 12, 2013, the "2013 Python Challenge," a Burmese python hunting competition, sponsored by the Florida Fish and Wildlife Conservation Commission began. It was a month-long event in which some 68 pythons were caught (ending February 16) and it encouraged amateurs and professional hunters to hunt the Burmese python. A $1500 reward was given to the hunter who caught the most pythons, and a $1000 reward was given to the hunter with the longest python.