Scientists with the University of Florida and the U.S. Geological Survey (USGS) have found that Burmese pythons are occupying bird nesting areas in the Everglades, suggesting that pythons are attracted to wading birds where they breed.
These findings reveal the current scope of the invasive snake’s impact on native wildlife, said Peter Frederick, one of the study’s co-authors, and a professor of wildlife ecology and conservation in the UF Institute of Food and Agricultural Sciences.
“We already knew that pythons are responsible for eating over 90 percent of the mid-sized mammals in the Everglades. Although we have known they eat wading birds where they forage, this is the first time we have documented pythons foraging on nestlings within densely packed colonies,” Frederick said.
In the Everglades, wading bird species, which include herons, egrets, storks and ibises, nest in clusters of trees. These clusters are called “tree islands” because they stand out in the flat, marshy landscape. Researchers wanted to know how common pythons were in tree islands where birds nest.
However, Burmese pythons are notoriously elusive, and there has been no efficient way for researchers to confirm their presence in a given location.
“Tree islands of the Everglades contain really dense vegetation. Conducting field work in tree islands often involves crawling through branches, vines and mud. Actually seeing a python is near-impossible,” said Sophie Orzechowski, the study’s lead author. Orzechowski performed this research as part of her recently completed master’s degree in the department of wildlife ecology and conservation in the UF/IFAS College of Agricultural and Life Sciences.
For help, the UF/IFAS researchers turned to USGS research geneticist Margaret Hunter, a co-author of the study. In her lab at the USGS Wetland and Aquatic Research Center in Gainesville, Fla., Hunter has developed a unique genetic marker for Burmese python environmental DNA.
Environmental DNA, or eDNA, is a research tool that uses sophisticated laboratory tests to detect trace amounts of genetic material left behind by the skin cells, saliva, mucus or waste an animal sheds as it passes through water, air or soil. The tests can show whether individuals from a particular species, such as Burmese pythons, have recently been in an area.
"Tracking pythons is very challenging, because like many wild animals, they have evolved camouflage and behaviors that keep them very well hidden,” said Hunter, an eDNA expert.
“But eDNA allows us to identify when the species we're looking for was recently present in a water body or a wetland. This is valuable information that is very difficult to get any other way, and can help
managers develop strategies for managing this invasive species."
To test the hypothesis that pythons favor tree islands with bird colonies over tree islands that lack birds, Orzechowski collected water samples at 15 nesting sites and 15 control sites in the Everglades, and analyzed them with guidance and lab and software resources provided by Hunter and USGS
statistician Robert Dorazio, now retired.
“Using eDNA, our results suggest that Burmese pythons are attracted to tree islands with active wading bird colonies,” Orzechowski said.
Orzechowski, Frederick and Christina Romagosa, UF/IFAS assistant professor of wildlife ecology and conservation, have also just published a study in the journal Biological Invasions that furthers the conclusions of the eDNA study. This second study used trail cameras to capture images of pythons preying on
nesting wading birds and showed that pythons have about five times the effect of native predators like raccoons and rat snakes. Together, the two studies show that pythons are attracted to nesting areas and are a nontrival source of nest loss.
Orzechowski said scientists believe that Burmese pythons were introduced into South Florida wild ecosystems beginning in the 1980s. Since then, they have been eating their way through the Everglades. Scientists hypothesize that native wildlife do not instinctively see pythons as predators.
“They aren’t evolutionarily prepared to deal with this kind of predator,” Frederick said.
To make matters worse, Burmese pythons are true eating machines, able to consume more than their own body weight in prey, he added. If they consume a lot of prey, as they appear to be doing in the Everglades, they can grow up to 3.5 to 7 feet long in their first year of life, and they reproduce rapidly.
This latest study indicates that some pythons are attracted to breeding colonies of birds, where they can have a large effect, Frederick said.
The pythons’ threat to wading birds is a threat to the goals of Everglades restoration, said Frederick, who has studied wading birds in the Everglades for the last 30 years.
“One of the stated restoration goals is the return of large wading bird colonies to the Everglades. The assumption is that the management of water flows
controls their food, and their nesting. But if pythons are resulting in big increases in predation, food and water management might cease to be the controlling force on bird populations. That could make hydrological restoration less effective as a tool to restore bird populations,” Frederick said.
The study was published in the journal PLOS ONE.