Capture-Mark-Recapture of Treefrogs at Bayou Teche National Wildlife Refuge

Science Center Objects

WARC researchers are gathering amphibian data to better understand the impact of natural disasters on treefrog populations and examine post-event processes.

The Science Issue and Relevance: Declines in amphibian abundance, as well as extinction and extirpation of certain species, have been observed in different habitats worldwide. Several hypotheses have been proposed to explain this trend including disease, climate change, environmental pollution, and habitat loss. The USGS Amphibian Research and Monitoring Initiative (ARMI) was formed in response to growing concerns about these threats and the potential loss of biodiversity. The goal of ARMI is to implement monitoring to gather baseline data and to investigate negative trends in amphibian populations. 

 

Methodology for Addressing the Issue: We initiated a study at Bayou Teche National Wildlife Refuge (NWR) in 2017 to gather baseline data on the population through a capture-mark-recapture study and promote partnerships within the Department of the Interior (DOI). The area surrounding Bayou Teche NWR is primarily agricultural and is located within 24 km of the Gulf of Mexico. In the event of a natural disaster like a hurricane, our baseline data would allow us to better understand the impact of such an event on treefrog populations and examine post-event processes.  

Capture-Mark-Recapture of Treefrogs at Bayou Teche National Wildlife Refuge

Cope’s Gray Treefrog with the orange alphanumeric tag A13 inserted into the thigh (Photo by Brad M. Glorioso)

PVC pipe

Typical placement of PVC pipe on tree in our study plots (Photo by Brad M. Glorioso)​​​​​​​

Our primary means of anuran sampling are polyvinyl chloride (PVC) pipes, a passive capture technique that allows frogs to enter and exit at their will. Hung from trees by nails, the pipes are attractive refugia to treefrogs, as they offer desirable temperature and humidity conditions as well as a sense of safety. We have four sites within the NWR that each have 50 PVC pipes. We check these pipes monthly and mark each new frog in the leg with a unique alpha numeric tag which has a combination of one letter (A-Z) and two numbers (00-99). We measure the snout-vent length of captured frogs and determine their sex, if possible. We most commonly catch squirrel treefrogs, green treefrogs, and Cope’s gray treefrogs, and recapture many of the frogs we mark. We installed an air temperature and humidity logger to gather hourly local climatic data. Soon after beginning the project, we began swabbing captured frogs for the fungal pathogen Batrachochytrium dendrobatidis (Bd), the causative agent of chytridiomycosis, which has caused declines and extinctions of frogs worldwide. We suspended this effort when initial testing showed no evidence of the pathogen in our samples.

 

Future Steps: We plan to continue our monthly sites visits. With each successive trip, we improve our ability to answer questions regarding movement, growth, survival, longevity, and phenology of the local treefrog community.