Yearly variation in amphibian sampling on the Targhee National Forest

Authors(s): R. J. Clark and C. R. Peterson

Publication:

Publisher:

Publication Date: 0000-00-00

Type: final report

Location: Pocatello ID

Abstract: This study was a continuation of an amphibian survey we performed in 1992 for the Targhee National Forest (TNF). Our primary objectives were to (1) describe yearly variation in amphibian sampling (ie, presence-absence and habitat associations), and (2) compare current information with records of historical amphibian occurrence (ie, museum records and documented observations). This study is important for several reasons. First, it provides a measure of the temporal variation in amphibian sampling. This information should assist forest biologists in designing appropriate surveys for amphibians. Second, it provides land managers with potentially important information when making land-use decisions that could affect populations of amphibians, especially those of sensitive species such as the spotted frog. Third, comparing changes in historical and current amphibian occurrences will help in the detection of trends in amphibian ppopulations. To accomplish our objectives, we compared amphibian sampling results obtained from surveys performed in a dry, warm year (1992) to those obtained during a wet, cool year (1993). We returned to 79 of the 98 sites that we first surveyed in 1992 (Clark et al, 1992). We employed the same survey methodology used in the 1992 survey (ie, timed searches). We aso addresssed the question of declines in amphibian populations by comparing results from this two-year survey with museum records that describe the previous occurrence of amphibians. Finally, we analyzed physical and environmental factors (ie, elevation, pH, and conductivity) that may influence amphibian distribution. Summary of results from this study: 1. We noted considerable yearly variation in the detectability of amphibians on the TNF. For example, chorus frogs were detected in neearly three times as many sites in 1993 (25) than in 1992 (9). 2. Although leopard frogs have occurred on the TNF in the past, we failed to observe any individuals in either 1992 or 1993. 3. The occurrence of amphibians on the TNF did not appear to vary significantly by elevation, aquatic pH, or aquatic conductivity. Conclusions: 1. The results of this study indicate that caution should be exercised when evaluating studies that either do not determine repeatability or report low repeatability. 2. The correct identification and sampling of breeding localities is important to the success of future suveys 3. We consider it very likely that northern leopard frogs have experienced significant declines on the TNF, and may now be extinct within the portion of its former range within forest boundaries.

Keywords: animal , herpetology, amphibian, frog, Anura, Bufonidae, Ranidae, toad, salamander, Caudata, Targhee National Forest, population, breeding, habitat, tiger salamander, Ambystoma tigrinum , western toad, Bufo boreas, chorus frog, Pseudacris triseriata, spotted frog, Rana pretiosa, leopard frog, Rana pipiens