Breeding Chorus Indices Are Weakly Related to Estimated Abundance of Boreal Chorus Frogs
Call surveys used to monitor breeding choruses of anuran amphibians generate index values that are frequently used to represent the number of male frogs present, but few studies have quantified this relationship. We compared abundance of male Boreal Chorus Frogs (Pseudacris maculata), estimated using capture–recapture methods in two populations in Colorado, to call index values derived from automated recordings. Single index values, such as might result from large monitoring efforts, were unrelated to population size. A synthetic call saturation index (CSI), the daily proportion of the maximum possible sum of index values derived from multiple recordings, was greater in larger populations, but the relationship was not highly predictive.Abstract
Mean (±1 SE) daily call saturation index (for eight years at Lily Pond and ten years at Matthews Pond combined) relative to the initiation of calling activity. Data from years without recordings or when recordings failed to determine the initiation of breeding activity were not used in this figure. Arrows indicate the mean dates for the first three CR occasions.
Mean (±1 SE) hourly call saturation index (years combined, but excluding 2006–2007, when recording did not include all 24 hr) of P. maculata at Lily Pond and Matthews Pond.
The maximum three-day mean call saturation index versus the estimated number of male P. maculata in breeding choruses at Lily Pond and Matthews Pond (R2 = 0.18; regression equation [solid line] CSI = 0.432 + 0.099 × log10(N^), P = 0.046). The dashed line indicates the regression with the slope (0.102) corrected for error in estimating N^.
Contributor Notes
Associate Editor: M. J. Lannoo.