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Compass issue 10
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Compass is a quarterly publication of the USDA Forest Service's Southern Research Station (SRS). As part of the Nation's largest forestry research organization -- USDA Forest Service Research and Development -- SRS serves 13 Southern States and beyond. The Station's 130 scienists work in more than 20 units located across the region at Federal laboratories, universites, and experimental forests.

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Issue 10

Froglogging in East Texas

by Zoë Hoyle

The decline of frog populations across the world has received a lot of attention in the last few years because of the key role frogs play in aquatic ecosystems as both predator and prey. Frogs and other amphibians, with their permeable skin and unshelled eggs, can also be seen as indicator species—canaries in nature’s coal mine—for the health of aquatic ecosystems. So far, no single cause has been found for declines in frog populations, though chemicals, disease, and loss of habitat have been identified as possible causes.

Changing weather patterns from global climate change could also be a contributing factor, particularly for frog species using ephemeral water sources. In eastern Texas, some frog species rely on ephemeral sources— sometimes literally a rain puddle— while others rely on permanent ponds.



“It’s widely known that the breeding activity of amphibians like frogs is closely tied to weather,” says Dan Saenz, SRS research wildlife biologist. “However, the specifics of these relationships have barely been explored.”

Saenz, along with other scientists from the Nacogdoches, TX, team of the SRS Southern Pine Ecology and Management group, is currently studying the effects of rainfall and temperature on the breeding activities of 13 different species of frogs in eastern Texas. Information from the research will make it possible to predict potential effects of a changing climate on frog populations.

“There’s a particularly high level of diversity in frog species in eastern Texas,” says Saenz. “There’s also a lot of seasonal variation in temperature and rainfall, so we suspected that weather might be a major factor influencing breeding activity in frogs.”

Frogs call at night to advertise for mates. To study breeding activity in relation to weather, Saenz and fellow researchers used “frogloggers” to record calls at eight different ponds every night for 2 years. Additional dataloggers recorded hourly air temperature and daily rainfall for each site.

After identifying calls from the tapes and relating them to weather data, the researchers were able to map out 5 different breeding patterns among the13 frog species that vary from total independence from local weather patterns to dependence on specific rainfall patterns in specific temperature ranges.

“Our research has shown how frog breeding activity is related to rainfall and temperature,” says Saenz. “A prolonged change in the weather will have different effects on different species—some negative, others positive or neutral. We don’t know how this will affect the diversity of frog species, but our research has given us a good foundation to begin making predictions.”

One type of wildland-urban interface is the isolated interface, where second homes are scattered across remote areas.
Gulf coast toad (Bufo valliceps). (Photo by Daniel Saenz, U.S. Forest Service)