Justification for Congressional python ban unscientific, researchers say

Biologists and veterinarians are urging the U.S. Congress to hold off on a ban on trade in pythons and other large exotic snakes until research into how much of a threat they pose to U.S. ecosystems has been thoroughly reviewed by independent scientists.

In a letter to the U.S. House Committee on the Judiciary (full text at the bottom of this blog entry), an independent group of scientists characterized a United States Geological Survey (USGS) report being touted as the justification for a ban on import and trade in pythons as “unscientific,” stated a news release issued by United States Association of Reptile Keepers (USARK).

USARK President Andrew Wyatt presented written testimony to Congress last month. “It is our belief that best management practices and professional standards specific to certain reptiles is what is needed, not draconian measures that will only succeed in destroying a viable industry,” he said. (Read a summary of Wyatt’s testimony.)

Congress is weighing a ban on the importation of large snakes like pythons and boas following a report by the USGS earlier this year that stated that climate conditions might be conducive to the spreading of feral Burnese pythons across much of the southern part of the United States.

“The independent group of scientists and herpetologists, including professors from the University of Florida, Arizona State, and Texas A&M among others penned members of Congress in response to comments made by the U.S. Fish & Wildlife Service (USFWS) during a November 6th hearing on H.R. 2811, a bill that could determine the fate of much of the reptile trade in the United States,” the USARK statement said.

“During that hearing USFWS Deputy Director Dan Ashe characterized the USGS report as “peer-reviewed science”, a claim that struck a nerve within the scientific community.

“It is a misrepresentation to call the USGS document ‘scientific’” stated the scientists,” USARK said. “As written, this [USGS] document is not suitable as the basis for legislative or regulatory policies, as its content is not based on best science practices, it has not undergone external peer-review, and it diverts attention away from the primary concern.

“We encourage the USFWS and USGS to submit this document to an independent body for proper and legitimate peer review. Additionally, we encourage the Committee to review this document, not as an authoritative scientific publication, but rather as a report currently drafted to support a predetermined policy.”

H.R. 2811, Introduced by U.S. Representative Kendrick Meek (D-FL), who recently announced his candidacy for the U.S. Senate, could add all pythons, and even boas, to the Injurious Wildlife list of the Lacey Act; a designation reserved for only the most dangerous alien invaders to our natural ecosystem, according to USARK.

“Such a move would prevent all import, export, and interstate transport of pythons in the U.S. The scientific justification for such a move hinges on a recently published report of the United States Geological Survey (USGS) entitled ‘Risk Assessment of Nine Large Constricting Snakes,’ which attempts to paints a picture of large constrictor snakes as an immediate threat to eco-systems over much of the U.S.”

Letter To Congress:

24 November 2009
U.S. House of Representatives Committee on the Judiciary
The Subcommittee on Crime, Terrorism & Homeland Security

Dear Chairman Bobby Scott and Ranking Member Louie Gohmert:

We write in regard to the recent Congressional hearing on HR 2811. As scientists who have worked with reptiles including those cited in HR2811, we express our reservations regarding the document recently released by USGS as an “Open-Report”, titled Giant Constrictors: Biological and Management Profiles and an Establishment Risk Assessment for Nine Large Species of Pythons, Anacondas, and the Boa Constrictor.

Simply put, this report is not a bona-fide “scientific” paper that has gone through external peer review. Part of this report is fact-driven, described by the authors as “traditional library scholarship.” By the authors’ admissions, there are surprisingly little data available regarding the natural history of these species. In their attempt to compile as much information as possible, the authors draw from a wide variety of references, ranging from articles published in peer-reviewed professional journals to far less authoritative hobbyist sources, including popular magazines, the internet, pet industry publications, and even various media sources.  While such an approach is inclusive, it tends to include information that is unsubstantiated and, in some cases, contradicts sound existing data.

As scientists whose careers are focused around publishing in peer-reviewed journals and providing expert reviews of papers submitted to these journals, we feel it is a misrepresentation to call the USGS document “scientific”. In fact, much of this report is based on an unproven risk assessment model that produces results that contradict the findings presented in a recently published scientific paper that used a more complex and superior model (see: Pyron R.A., F.T. Burbrink, and T.J. Guiher. 2008. Claims of Potential Expansion throughout the U.S. by Invasive Python Species Are Contradicted by Ecological Niche Models, PLoS One 3: e2931.doi:10.1371/journal.pone.0002931). 

Unfortunately, the authors of the USGS document limit their reference to this scientific work to an unsubstantiated criticism.  To the contrary, this alternate model is validated by its relatively accurate prediction of the natural distribution of the species in question (something the USGS model does not even attempt).   Furthermore, despite its conclusion of a limited potential distribution of Burmese pythons in the United States, the model presented by Pyron et al. accurately predicts the presence of Burmese pythons in the Everglades.

The USGS model likely provides a gross overestimate of potential habitat for these snake species.  People throughout the United States keep pythons as pets, yet the only known breeding populations in the United States are in the Everglades.  Such a wide distribution of potential sources of invasion, but only a localized invasive event, suggests that factors beyond those used in the USGS model are critical to limiting the suitability of habitat for pythons.  The authors even state that climate is only one factor of several that affect the distribution of an animal, yet they develop a model that only uses overly simplistic climatic data (e.g., the climatic data did not take seasonality into consideration).

We are further concerned by the pervasive bias throughout this report. There is an obvious effort to emphasize the size, fecundity and dangers posed by each species; no chance is missed to speculate on negative scenarios. The report appears designed to promote the tenuous concept that invasive giant snakes are a national threat. However, throughout the report there is a preponderance of grammatical qualifiers that serve to weaken many, if not most, statements that are made.

We fully recognize the serious concerns associated with the presence of persistent python populations in southern Florida.  As top predators, these animals can and will have a dramatic impact on the community of wildlife that lives in the Everglades.  Inaccurately extending this threat to a much large geographic area is not only inappropriate, but likely takes needed focus away from the real problem in the Everglades.  

In conclusion, as written, this document is not suitable as the basis for legislative or regulatory policies, as its content is not based on best science practices, it has not gone through external peer-review, and it diverts attention away from the primary concern. We encourage the USFWS and USGS to submit this document to an independent body for proper and legitimate peer review.  Additionally, we encourage the Committee to review this document, not as an authoritative scientific publication, but rather as a report currently drafted to support a predetermined policy.

Elliott Jacobson, MS, DVM, PhD, Dipl. ACZM
Professor of Zoological Medicine
University of Florida

Dale DeNardo, DVM, PhD
Associate Professor School of Life Sciences
Arizona State University

Paul M. Gibbons, DVM, MS, Dipl. ABVP (Avian)
President-Elect, Association of Reptilian and Amphibian Veterinarians
Interim Regent, Reptiles & Amphibians, American Board of Veterinary Practitioners
Director, Exotic Species Specialty Service
Animal Emergency Center and Specialty Services

Chris Griffin, DVM, Dipl. ABVP (Avian)
President, Association of Reptilian and Amphibian Veterinarians
Owner and Medical Director
Griffin Avian and Exotic Veterinary Hospital

Brady Barr, PhD
Resident Herpetologist
National Geographic Society
Endangered Species Coalition of the Council of State Governments
Crocodilian Specialist Group

Warren Booth, PhD
Invasive Species Biologist
Research Associate
North Carolina State University
Director of Science
United States Association of Reptile Keepers

Ray E. Ashton, Jr.
Ashton Biodiversity Research & Preservation Institute

Robert Herrington, PhD
Professor of Biology
Georgia Southwestern State University

Douglas L. Hotle
Curator of Herpetology/Conservation/Research
Natural Toxins Research Center
Texas A&M University

Francis L. Rose (Retired) , B.S., M.S.  (Zoology), PhD (Zoology)
Professor Emeritus
Texas State University

Edward J. Wozniak DVM, PhD
Regional Veterinarian
Zoonosis Control Division
Texas Department of State Health Services
CC: Secretary Kenneth Salazar, US Dept of the Interior; Director Marcia McNutt, US Geological Survey; Director Sam Hamilton, US Fish & Wildlife Service

“National Geographic Explorer: Python Wars” airs in the United States on February 9, at 10 p.m. on National Geographic Channel. Click on the video above to watch an excerpt. Click here to view more excerpts and get additional information.


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More than forty years in U.S., UK, and South African media gives David Max Braun global perspective and experience across multiple storytelling platforms. His coverage of science, nature, politics, and technology has been published/broadcast by the BBC, CNN, NPR, AP, UPI, National Geographic, TechWeb, De Telegraaf, Travel World, and Argus South African Newspapers. He has published two books and won several journalism awards. In his 22-year career at National Geographic he was VP and editor in chief of National Geographic Digital Media, and the founding editor of the National Geographic Society blog, hosting a global discussion on issues resonating with the Society's mission and initiatives. He also directed the Society side of the Fulbright-National Geographic Digital Storytelling Fellowship, awarded to Americans seeking the opportunity to spend nine months abroad, engaging local communities and sharing stories from the field with a global audience. A regular expert on National Geographic Expeditions, David also lectures on storytelling for impact. He has 120,000 followers on social media: Facebook  Twitter  LinkedIn