Debunking the Claim that Burmese Pythons are causing Severe Mammal Declines in the Everglades

The National Academy of Science often publishes some really bad studies.  Two years ago, the journal of this organization published a paper entitled “Severe Mammal Declines Coincide with the Proliferation of Burmese Pythons in Everglades National Park.”  This study was authored by Michael Dorcas, an herpetologist from Davidson College, along with a long list of other scientists.  I’m always leery of studies with a long list of contributing scientists.  I suspect the lead authors of these studies do most of the work, and misleadingly include many co-authors.  With minimal input, the many co-authors lend legitimacy to a study in exchange for getting the publishing credit that is so important for their academic careers.

Michael Dorcas.  This scientist authored a really bad study of Burmese pythons that led him to conclude they were wiping out mammal populations in the Everglades National Park.  His study was debunked by the Florida Fish and Wildlife Conservation Commission.  Nevertheless, the media took his ridiculous conclusions as gospel.  Not a single journalist questioned this terrible amateurish study.

I read Dr. Dorcas’s study and knew the results didn’t fit within ecological reality.  He went back to records of road-killed animals in Everglades National Park during the 1990’s before the population of Burmese pythons had become significant and compared them with the number of road side sightings of these same species 10 years later.  He concluded that the populations of raccoons, possums, bobcats, and marsh rabbits had been decimated and in some cases had been reduced by 100%.  This doesn’t make any sense ecologically.  If the population of prey declines in abundance, than the population of predators declines as well because there is nothing for the predators to eat.  Burmese pythons couldn’t decimate mammal populations without eventually succombing to starvation themselves.  So the results of Dr. Dorcas’s study were unbelievably ridiculous.  Nevertheless, every news media outlet picked up this alarmist nonsense and not a single journalist questioned the credibility of such an absurd conclusion.  This demonstrates the ignorance of basic ecology among the average layperson.  I mentioned my logical objections to this study’s findings on my blog about a year ago but thought I was a lone voice in the wilderness.  However, I discovered someone from The Florida Fish and Wildlife Conservation agrees with me.  They found the following flaws in Dr. Dorcas’s study.

1. The survey for road-killed animals (Dr. Dorcas’s data from the 1990’s) didn’t include critical information–how many observers, the number of miles driven, the number of days the survey was done, and the procedures used to avoid double counting.  In other words this data is anecdotal and useless.

2. The year of the pre-python survey was a high water year when more animals were forced to take refuge on the high ground where the road exists.  This explains why more animals were counted during the survey than during later drought years.  Road-side surveys yield dubious data.  Dr. Dorcas should have used live trapping to get an accurate count of mammal populations.

3. There is no actual data on python densities.

4. The timing of the python population increase and the supposed decline in mammal populations is not documented.  Scientists can’t explain how python populations could increase following prey population declines (my point exactly).

5. There is no mention in Dr. Dorcas’s study of coyotes.  Coyotes recently re-colonized south Florida and may play a role in the decline of mammal populations there.

6. The differences in prey density inside and outside Everglades National Park are likely due to differences in habitat, not the presence of pythons.  Everglades National Park is actually very poor wildlife habitat.  More wildlife lives outside the park than inside.  With very few exceptions most of the best wildlife habitat left in the world is occupied by humans.  We give animals the wastelands that are too expensive to commercially develop and call them national parks.

Burmese python killed by alligator.  Burmese pythons are beneficial additions to Florida’s ecology, despite what alarmist environmentalists claim.  South Florida’s ecology was in desperate need of a large predator.

Contrary to the claims of alarmist environmentalists, Burmese pythons are a beneficial addition to South Florida’s ecosystem.  During the Pleistocene in this region there were 5 species of big cats plus dire wolves, bears, and alligators.  Now, there are just alligators and pythons.  (Very few Florida panthers live in Everglades National Park.  Most occur on cattle ranches located well north of the park.) Without the presence of large predators, the populations of smaller predators such as raccoons and possums increased.  These predators eat reptile eggs and put a big dent in the population of 17 endangered and threatened species of reptiles, including rare sea turtles.  Pythons help control the numbers of raccoons and possums, helping increase the nesting success of endangered reptiles.  Pythons are beneficial for twice as many endangered species than ones they might prey upon.

Scientists’ estimates of Burmese pythons populations in Florida are not based on scientific data.  They are wild guesses bordering on fantasy.  The oft-cited number of 30,000-150,000 is a wild overstimate.  Over the past 12 years, 2000 pythons have been removed from Everglades National Park.  That’s less than 200 per year–nowhere near what one would expect, if there were 30,000 large snakes slithering inside the park.  Last year, there was a python round up.  For a month 1500 snake hunters looked for Burmese pythons to kill.  They netted just 50.  This is strong evidence Burmese pythons are not even close to being as abundant as researchers claim.


Dorcas, Michael; et. al.

“Severe Mammal Declines Coincide with Proliferation of Invasive Burmese Pythons in Everglades National Park”

PNAS December 2011

Unnamed author

“Commentary on Mammal Declines in Everglades National Park”

Florida Fish and Wildlife Conservation Commission report 2012


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9 Responses to “Debunking the Claim that Burmese Pythons are causing Severe Mammal Declines in the Everglades”

  1. Bob Says:

    “Contrary to the claims of alarmist environmentalists, Burmese pythons are a beneficial addition to South Florida’s ecosystem.” You’re claim isn’t backed up by any scientific research. You’re doing the same thing that you complain about in your blog, lack of sound scientific data and analysis. Also, you make it sound as if alligators don’t feed often on raccoons and opossums and the large American alligator population and the increasing American crocodile population in the Everglades don’t make a dent on the raccoon and Virginia opossum population.

    You are right that non-native snakes are feeding on raccoons and opossums, but these snakes are also feeding on species you seem to think the non-native snakes are “protecting”. For example, non-native snakes are opportunistic and feed on state and federally listed wading birds, species that raccoons and opossums may not typically feed upon to due the location of bird rookeries in deeper water.

    Your comment indicating that the number of pythons removed in the Everglades is indicative of the size of the python population in the Everglades is vastly misleading. Please provide the scientific data backing up this correlation. Also, the python hunters you mentioned had a wide disparity regarding experience catching pythons, experience in python ecology, and experience in Florida natural habitats. All of those topics determine where, when, and how to hunt pythons. If people are missing that information then their python catch ability decreases. Also, the Everglades is vast. Even an extremely low number of pythons per acre can still result in a rather large python population occupying the Everglades.

    • markgelbart Says:

      That Burmese pythons ARE a beneficial addition to south Florida’s ecosystem is my opinion but it is backed by scientific research. Some species of turtles are increasing in numbers because of python predation on small mammalian predators. See: Dorcas, Michael; et. al.

      “Severe Mammal Declines Coincide with Proliferation of Invasive Burmese Pythons in Everglades National Park”

      PNAS December 2011

      I never wrote that alligators don’t feed on raccoons and opossums. I can’t debate points that you invent in your imagination.

      Snakes don’t eat that much because they have a low metabolism. There’s no evidence Burmese pythons are having any significant impact on wading bird populations.

      If pythons really were as abundant as alarmists claim, the great python round-up would have yielded many more specimens. That’s common sense. Why would you need scientific data for something that merely requires logic? But, if you want a correlation that compares hunting results with population of a species, why don’t you just look up every state’s statistics on white tailed deer and turkey harvests? Every state game and fish commission has these statistics. Of course, there is a close correlation between hunter harvests and overall population of species. You have to be really dumb not to understand that.

  2. Bob Says:

    First, you’re now citing paper your critiqued very negatively as proof that pythons are beneficial….that makes absolutely no sense.
    “Snakes don’t eat that much because they have a low metabolism.” First, metabolism depends on a number of factors including size of the animal, physical activity, and outside temperature. To say pythons have a low metabolism therefore they aren’t a threat to native Florida wildlife is ridiculous.

    You’re continued theory that few pythons captured in the FWC python roundup means there are few pythons in the Everglades is ridiculous. Have you ever caught a Burmese python or seen one in the wild? I’ve caught two and they are very hard to find. I was basically stepping on one (an 11 foot long Burmese python) before I saw it. They are very cryptic and thus hard to find. Also, the Everglades is vast therefore the search area covered by the python round up participants is extremely small.

    You don’t know much about wildlife management if you are comparing the ability to hunt white-tailed deer or turkeys to the ability to hunt Burmese pythons. You’re comparing apples to oranges. You showed your true knowledge when you made that comment.

    • markgelbart Says:

      My first point makes no sense to you because you are too stupid to understand it. The paper admits that pythons help increase turtle populations. That is beneficial.

      Burmese pythons are hard to find because they are not as common as alarmists claim.

      You caught a whole 2 pythons? Wow! That’s proof there are 150,000 in the Everglades, isn’t it?

      The best evidence of an animal’s estimated population would be the number of specimens captured or killed. I’m sorry you are too obtuse to accept that logic.

      • Bob Says:

        You keep citing a paper that you ridiculed!! You found one thing that you agree with in the paper so now you cite it. The rest of the paper you think is garbage so you ridicule it. That makes your opinion not worth listening to at all.

        it’s obvious you know nothing about Burmese pythons because you can’t understand that their cryptic coloring and coupled with a python’s behavior make Burmese pythons extremely difficult to locate in the wild. You use the example of my catching only two pythons as proof that there is a low number of pythons in south Florida. We all had a good laugh when we read that comment. It’s hilarious that you somehow feel that there is an exact correlation with the size of a population and capture probability, no matter what the species.
        You seem to think that a low number of animals captured always means a low number of animals occupying an area. To prove this you used a bizarre comparison of white-tailed deer/turkey hunting success to success at capturing Burmese pythons. You don’t understand or can’t grasp the concept that an animals coloring and camouflage, behavior, types of habitat utilized, etc. play a huge part in capture probability of an animal. You don’t understand that human capture effort, knowledge of a species, access to habitat, etc. also plays a huge part in hunting success. You don’t understand the Everglades is extremely vast (bet you’ve never been there) and large parts of the Everglades are difficult to access by humans. None of this matters because you don’t believe in what scientists studying the species have to say. Instead you base all of your comments on personal opinion and disregard science. That’s incredibly sad and embarrassing.

  3. Bob Says:

    To markgelbart,

    Please see the attached link. You really need the education on pythons.

    Click to access uw28600.pdf

    • markgelbart Says:

      I’ve already read that piece of alarmist propaganda. The authors present no evidence that pythons are detrimental to the ecosystem. Pythons provide a much needed addition to the predator guild of south Florida.

      • Bob Says:

        So you classify publications from scientists as “alarmist propaganda” but consider your opinions sound and rational arguments on the subject. That’ makes no sense.

  4. markgelbart Says:

    You think my opinion is not worth listening to at all and yet you have spent a considerable amount of time responding to it.

    Hey, the only way to determine the population of an animal is to collect data. This includes capturing them physically or on camera. If you aren’t capturing many that way, then that means there just aren’t many there. (The roundup results definitely support my argument.) You can’t estimate population size on guesswork which is what you want to do. Claiming they are hard to find or see and that the Everglades is vast are excuses.

    I could make the claim there are 2000 Bigfoot apes in the Everglades but because it is so vast and they can hide in the shadows we can’t find them. This logic = your logic.

    There’s nothing in the link that convinces me Burmese pythons are detrimental to the environment. They eat the same prey items that Florida panthers or alligators eat. They live in areas that are practically devoid of Florida panthers and therefore occupy that niche. Most Florida panthers live on cattle ranches north of protected areas.

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