Diel Patterns of Detectability for the Different Life Stages of a Common Anuran (Pseudacris Sierra) in Visual Encounter Surveys

Estimates of relative abundance are fundamental to ecology, but estimation methods that assume constant detectability of individuals across space and time may be overly simplistic. This study examines the relationship between time of day and detectability for multiple life stages of Sierran Chorus Frogs (Pseudacris sierra) in visual encounter surveys (VESs). Using generalized additive models, we found a significant nonlinear relationship between time of day and detectability for P. sierra larvae, with detection peaking during midday and waning in the early morning and late afternoon. The timing of peak larva detection was not significantly different between our 2 study regions, Lassen Volcanic National Park and Quail Ridge Ecological Reserve, California. We also examined the relationship between time of day and detectability for each of 3 juvenile metamorphic stages: larvae with no limb development, larvae with limb development, and froglets that had completed metamorphosis. Detectability of both larval stages had significant nonlinear relationships with time of day, but the relationship between time of day and the detection of froglets was determined to be significant and linear, increasing throughout the day. Overall, these results suggest that the relationship between time of day and detectability should be considered when estimating relative abundance, and that this relationship may be species- and life-stage-specific.