Patuxent Wildlife Research Center

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Funnel Trapping Larval Amphibians in Prairie Pothole Wetlands

Erin Johnson, Shawn Jones, Todd Gunderson, Kenneth Klang, and Michael J. Lannoo

Recent concerns over reported amphibian declines have prompted a renewed interest in methods that can be employed for amphibian sampling and monitoring. Unbaited funnel (or minnow) trapping has several advantagesover other aquatic sampling techniques. We report funnel trapping success of four common amphibians, the eastern tiger salamander (Ambystoma tigrinum),the northern leopard frog (Rana pipiens), the American toad (Bufo americanus), and the western chorus frog (Pseudacris triseriata) in 17 prairie pothole wetlands in northwestern Iowa. Our goals were to: 1) document the usefulness of this technique for sampling aquatic amphibians; 2) determine biases in this technique; 3) determine the effect of wetland type on trapping success; 4) and to determine the effort needed to statistically document a change in the population. Our data show that minnow trapping can be an effective method for sampling amphibian larvae in discrete wetlands. Factors such as trap orientation and diurnal variation did not generally influence trapping success. Several biases, including size and species biases, arise with trapping amphibian larvae. These biases must be considered when inferring population characteristics across years and wetlands, and when comparing species. Additionally, we emphasize that certain results from larval monitoring may or may not be relevant to amphibians populations as a whole.

Key Words: funnel trapping, population, monitoring, survey, Rana pipiens, Ambystoma tigrinum, wetlands, sampling design

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U.S. Department of the Interior
U.S. Geological Survey
Patuxent Wildlife Research Center
Laurel, MD, USA 20708-4038
Contact: Sam Droege, email:
Last Modified: June 2002