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Using Pipe Traps to Monitor Treefrog Populations:
A Cautionary Tale

George Cline, Jason Adams, Eric Blackwell, and Paul Rogers

Much effort has been directed towards developing a standard methods for monitoring amphibian populations. This effort has produced some valuable data and has produced some interesting methodologies. One method that has received a lot of attention in recent months has been the use of PVC pipe traps to monitor treefrog populations. Presumably, these pipes represent refugia from desiccation during the day. We attempted to use this technique as part of a survey of herptiles in northeast Alabama.

The study site was an unnamed pond on Dugger Mountain, Calhoun/Clebourne County, Alabama. Dugger Mountain is part of the Talladega National Forest and is currently being considered for Wilderness Area designation. Two diameters of pipes were used in this study (2.5 cm and 3.8 cm). Twenty-five 60 cm long pipes of each diameter were attached vertically to trees ca 2 m above the ground. A foam plug was saturated with water, placed in the ventral opening, and secured with duct tape. Forest Service regulations restricted us from using nails to hang pipes up, so duct tape was used to secure the pipe traps to the trees. Pipe traps were placed in shaded areas no farther than 30 m from standing water. Since our only concern was to determine presence or absence, these traps were not checked on a regular basis between May and early July.

We found no frogs in any of the pipes during this study. In fact, the only herptile collected using this technique was a medium-sized Ringneck Snake (Diadophis punctatus) found stuck to the duct tape that secured the trap to the tree. Additionally, we found that we suffered high trap loss (32%) at this site. A few of the traps were found planted in the soil near the edge of the pond. Apparently fishermen used these pipes to hold fishing rods while catching catfish. No obvious preference by fishermen for a particular pipe diameter was observed in this study. This problem, while not monetarily expensive, did cost us several trap nights and could have a significant impact in areas where treefrogs use the traps. Special care should be taken to make the pipe traps as inconspicuous as possible.

We cannot explain the lack of trapping success observed in this study. Several treefrog species were observed in the area (Hyla chrysoscelis, Hyla cinerea, Hyla gratiosa, and Pseudacris crucifer), and at least one of these species (H. cinerea) has used pipe traps in other studies, and another species (H. chrysoscelis) has used bluebird boxes as daily refugia. We plan to continue this study at another site where public access is limited.

Editorial Note: In some ways, this technique is not different from other techniques where habitat is supplemented (i.e., placing boards for terrestrial salamanders or adding bromeliads to attract dendrobatid frogs). The danger might be that it might provide additional shelters where resting sites are limiting, or it might reduce mortality associated with desiccation. In both cases, the result would be an increase in survivorship that would bias the results of the study. Great care must be taken in interpreting results using this technique.

 

U.S. Department of the Interior
U.S. Geological Survey
Patuxent Wildlife Research Center
Laurel, MD, USA 20708-4038
http://www.pwrc.usgs.gov/naamp3/naamp3.html
Contact: Sam Droege, email: Sam_Droege@usgs.gov
Last Modified: June 2002