Abstract:
The overwintering behavior and ecology of American Bullfrogs are poorly understood. A Jolly-Seber capture/recapture population estimation was conducted during fall 2001 and summer 2002 to estimate winter mortality of American Bullfrogs at a pond located on the property of Wolf Creek Nuclear Operating Corporation in Coffey County, KS. American Bullfrogs (12 adults ~ 69g) were collected and a radio transmitter was implanted into each frog. Frogs were located once a week and ten habitat variables were recorded at each frog's location (frog points), at one point, < 1 m, 1-4 m, and> 4 m from the frog's location (non-frog points), and in areas where frogs were not located (pond points). Locations were recorded on aerial photos and Spearman rank correlation was conducted to determine if movements were correlated among frogs. Principal Components Analysis was conducted on the habitat variables. ANOVA revealed that the only significant differences between frog, non-frog, and pond points were on PC-1 and PC-2, with a Tukey's studentized range test
grouping frog and non-frog points as a significantly
different group than the pond points on PC-l and PC-2. The
high, positive loading score for temperature and the high,
negative loading score for dissolved oxygen on PC-l show
that as temperature increased at sample sites dissolved
oxygen decreased. The high, positive loading scores for
depth and % gravel substrate show a positive correlation
between these variables. American bullfrogs were selecting
shallow areas of the pond with lower temperatures and
higher dissolved oxygen. The estimate of winter mortality could not be estimated due to an absence of ranids at the
pond during summer sampling. Movements were uncorrelated
among frogs during the winter sampling and the purpose for long-range movements is unclear.
