To Move or Not to Move, That’s the Frog’s Question

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Adult Gopher Frog following capture. Photo by Garrett Lawson

Author: Garret Lawson

Habitat alteration is one of the greatest threats facing wildlife species that have specialized food and shelter preferences. Discovering whether—and how—native species use human-modified habitats is an important part of understanding their likelihood of persisting in changing landscapes. This is an especially interesting question for amphibians that use both aquatic and terrestrial habitats, like the Gopher Frog.

An adult Gopher Frog is relatively large, about the size of your palm. This native species is distinguishable from other frogs by its dark gray spotting and two gold/tan lines running parallel down its back. Unlike bullfrogs and some other highly aquatic frog species, Gopher Frogs don’t live full-time in ponds. Instead, for most of the year they live in the burrows of other animals, such as Gopher Tortoises, armadillos, and small rodents commonly found in fire-maintained scrub and sandhill. Found throughout the Southeast United States, Gopher Frogs populations are in decline range-wide due to a loss of the upland, fire-maintained habitats they rely on. Although many of our scrub and sandhill habitats have been cleared of native vegetation, those cleared areas might still be occupied by Gopher Frogs if tortoise burrows or other underground holes are available.

A recent study at Archbold Biological Station focused on Gopher Frogs to learn whether this secretive, nocturnal species has different movement behaviors in areas cleared for pastures and fields versus native shrub-dominated habitat. Archbold intern Garrett Lawson (a recent graduate of Arkansas Tech University) captured and tracked Gopher Frogs found at tortoise burrows in these contrasting habitats. The study field was once sandhill habitat but was cleared of native vegetation and planted with non-native grasses decades ago.

But, how does one track a frog? The method Lawson used requires a non-toxic glowing powder. As he explains, “I captured frogs just after sunset, dipped their bellies in the non-toxic fluorescent powder, and released them.” With each jump of the frog, flecks of fluorescent powder are left behind on the ground. Lawson further explains, “I came back the following morning before sunrise to find and measure their trails with a black light. By following the glowing trail of powder left after their nightly activity, I could track the individual movements of each frog.” Lawson predicted that differences in vegetation density or insect prey abundance in different habitats might influence the frequency or distance of Gopher Frogs’ nightly movements. The research was conducted using sterile gloves and equipment and following permit protocols.

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Powder trail left by a Gopher Frog after nightly activity.
Photo by Garrett Lawson

Lawson captured and tracked more than 80 individual Gopher Frogs over the spring and early summer of 2019. Lawson says, “The frogs were pretty sedentary in both habitat types, staying within a few feet of their burrows. The likelihood of a frog venturing away from its burrow was affected mostly by temperature, with an increase in movement frequency and distance as temperature increased. And the effects of high temperature were more pronounced in sandhill habitat.” When asked about the most interesting finding of his study, Lawson said, “My data suggest that the frogs moved greater distances in the least disturbed habitat, namely unburned sandhill. This might have to do with the higher density of native vegetation, including shrub cover, in sandhill providing more protection from predators.”

Lawson believes more work is needed to fully explore the movement behaviors of Gopher Frogs. “I did my sampling during the dry season so we would need a study covering at least a full year to see how weather affects their movements. These frogs are known to travel up to 3.5 kilometers to get to their breeding ponds in the wet season. I did notice a lot of frogs left my upland study area in June when there was some rain, presumably heading to their breeding ponds.”

 

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