The Big Squeeze: Pythons and Mammals in Everglades National Park
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The Big Squeeze: Pythons and Mammals in Everglades
Welcome and thanks for listening to this episode of
CoreCast. I'm Marisa Lubeck.
The wet, subtropical wilderness of Everglades National
Park is home to a diversity of Floridian wildlife, but one
invader is causing severe changes in these native animal
populations. Many of the park’s mammals are declining dramatically as
a result of invasive Burmese pythons, according to a
recent study by U.S. Geological Survey scientists and
partners. Mid-sized mammals such as foxes, rabbits, and raccoons
that were previously populous in the Everglades are the
most severely affected.
I'm here with USGS scientist and co-author, Robert Reed,
to discuss the Burmese Python situation and what these
mammal declines mean for the Everglades ecosystem. Thanks for talking with me, Bob.
What's the extent of the problem and why are these mammals
Well, the general findings were that a number of mid-sized
mammal species in the Everglades appear to have declined
precipitously over the last eight years as compared to
surveys done in the mid-1990s. Species that were declining the most were mid-sized
animals like raccoons, opossums and marsh rabbits.
And then some species, such as foxes and bobcats, weren't
seen at all in recent years.
The spatial scale includes a large proportion of the
Everglades and so we have two main aspects of the study. One was temporal or time-based. We repeated a study
that was done in the mid-1990s that consisted of driving
roads in the Everglades and just recording the number
mammals we saw per kilometer driven. Then we also did a spatial aspect that includes looking
at the heart of the area that's occupied by pythons in the
Before and after showed that mammals had declined a lot
since the 90s and the spatial showed that there are very
few in the heart of the Everglades where the pythons have
been there the longest. There are more on the edge of the python's range where
they've only recently arrived and there are a lot more
outside the area where we see pythons.
So does this mean that these animals are at risk of
becoming endangered in the area?
Well, the marsh rabbit is endangered in the lower Florida
Keys, but because most of these species are common
somewhere else, it's unlikely that they'd be formally
classified as endangered under the Endangered Species Act. However, if you define the word endangered more generally
as something that's at risk of local extinction, some of
these species may qualify for that designation, especially
in the southern Everglades.
Bob, what are the risks to the overall Everglades
ecosystem? For example, could other species be
Everglades is a really complex ecosystem. The
potential effects of removing some of these mid-sized
mammals are largely unknown. Animals like marsh
rabbits were formally really abundant. We've got records where people said they drove down a
single levee in the morning and saw over a hundred marsh
rabbits. And those same levees with rabbits are
basically gone now. The rabbits were certainly an important part of the food
lab for a variety of predators. Losing them could
make it hard for the other predators to find food.
On the other hand, raccoons are notorious nest
robbers. They're egg eaters. So we could see
an increase in turtles or other egg-laying animals. We can take a hint on what might happen from the island
of Guam where the invasive brown tree snake wiped out most
of the island's birds. Many of the native trees on
the island are now failing to replace themselves, because
their seeds aren't being dispersed by birds.
And it's impossible to walk through the forest on Guam
now, without ending up completely coated in spiderwebs
from head to toe. Without birds to pick with spiders
and to compete with the spiders for insect prey, big or
weaver spiders are everywhere. And this is the sort
of long-term effect of an invasive snake on the ecosystem
that is really difficult to predict.
What sort of control measures could work in the
park. For example, could people hunt and eat the
pythons to keep their number sound, things like that?
There are two main obstacles to trying to get rid of
pythons at the scale of Everglades National Park.
The first is that the park is a vast area. Thousands
of square kilometers. And most of it is largely
inaccessible to people. We only have access to a very small proportion of the
pythons that are in the park. Most of them are
encountered on roads or on levees. Those roads and
levees only account for maybe a percent or two of the
total area of the park.
The other problem is that pythons and snakes, in general,
are generally hard to detect. I've been in the
Everglades with three or four other people, standing in a
circle that's maybe 6 or 8' in diameter, we're in a foot
of water and between us there's a 12-foot Burmese python
that has a radio transmitter inside it. We know it's
there, but we cannot see it. So, there are obviously obstacles, but that doesn't mean
that all hope is lost. We may be able to prevent
their spread to the Florida Keys. We may be able to
prevent their spread farther north and we may be able to
protect locally important ecological resources.
For example, if we've got endangered wood storks that are
nesting communally in a small area, perhaps we can deploy
traps and other snake control tools to make sure that
those birds are not being impacted by pythons. Local control may be possible.
Have any such control measures that instituted yet?
Well most of the snakes that are currently being taken out
of the Everglades are taken from roads and levees.
And so, it's possible that we're at least having a local
effect on population densities. About 1,500 pythons
has been taken out of Everglades National Park and the
areas around the park over the last decade alone.
Last year we conducted a trap trial where we put up 60
traps for about 60 days. Unfortunately, we didn't
catch many pythons but we did catch some. And then
suggest that if we continue to improve the traps, our
success in controlling the snakes will continue to
Speaking of remoteness, is it possible that the problem
could actually be affecting more species than your
findings indicate, given that it's so hard to get to most
of the areas within the park to conduct your research?
The results of our study only applied to mammals that
could be seen on roads at night. There are also a
number of mammals that rarely cross roads, especially the
aquatic animals. And so, we don't detect them.
And yet, animals like that might be at severe risk of
being eaten by pythons. The round-tailed muskrat is perfect prey size for
medium-sized python and the pythons spend a lot time in
the water. Very few round-tailed muskrats were
detected in recent mammal surveys in the Everglades.
But, they showed up with increasing frequency in python
diets in the 2000s before they started decreasing in
frequency in the python diets. That suggests that
they may be declining as well, but we don't have good
evidence based on observations or real population sizes
yet. So, that's one of the main goals of future research is to
start concentrating on some of those other species to
determine what's going on with their populations.
Are human visitors to the park at risk?
Chances of a human being attacked by a python in the park
are extremely low. Even in their native range,
Burmese pythons are not known to attack people very often. In the U.S., there have been deaths attributed to the
Burmese Python, but all of those are from captive
animals. There have been no attacks on people in the
wild in the U.S.
These pythons are invasive, meaning they aren't native to
the Everglades. Where did they come from?
There's been a lot of controversy about the origin of the
pythons that are in the Everglades. Some folks are
convinced that hurricane Andrew in 1992 is the source of
the population, because we know that there were python
breeder facilities that were knocked over by the
hurricane. On the other hand, the first pythons observed and the
apparent founding population was way down in the southern
Everglades, roughly in the area that's at the end of the
main park road. That area's almost 50 kilometers
from where are the import businesses were.
We will never know the answer to this question for
sure. We do know that the snakes were ultimately
brought in to the country, intentionally, for the pet
trade. How they went from the pet trade into the
wild is not as important. We know why they were
brought in originally.
And when did the pythons start showing up in the
The snakes were probably established in the park prior to
1990. But, they probably took a while to build up
their numbers and attain densities that allowed us to
start seeing them regularly. Starting in the 80s,
there were a couple found, in the 90s, there was a trickle
of animals and then in the 2000s, that trickle turned into
Bob, as the scientist attempting to answer these questions
about a complicated python problem in a very complicated
ecosystem, what lessons have you learned along the way?
One of the most depressing facts to those who are studying
invasive reptiles around the world is that there has never
been an established and wide-spread population of invasive
reptile that has been eradicated. Eradication is
really difficult and requires a lot of resources.
And that points to the need for prevention. If we
can prevent these things from becoming established or
becoming wide spread or abundant, then we may have a
chance of preventing future scenarios like what we're
seeing with Burmese pythons in the Everglades.
Thanks for your time, Bob.
Sure thing, Marisa.
CoreCast is a product of the U.S Geological Survey
Department of the Interior. I'm Marisa Lubeck.
Thanks for listening.
Title: The Big Squeeze: Pythons and Mammals in Everglades National Park
The wet, subtropical wilderness of Everglades National Park is home to a diversity of Floridian wildlife, but one invader is causing severe changes in these native animal populations. Many of the park’s mammals are declining dramatically as a result of invasive Burmese pythons, according to a recent study by U.S. Geological Survey scientists and partners. Mid-sized mammals such as foxes, rabbits, and raccoons that were previously populous in the Everglades are the most severely affected. USGS scientist and co-author Robert Reed to discusses the Burmese python situation and what these mammal declines mean for the Everglades ecosystem.