Zoological Studies

Effective Point-Count Duration for Estimating Bird Species’ Richness in Chilean Forest

Pablo M. Vergara, Jaime E. Jiménez, and Roberto P. Schlatte (2010) When point counts are used to assess species richness or diversity, optimizing the allocation of sampling effort requires that the effective point-count duration be determined that optimizes the species detection rate at each point.  In this study, we used species accumulation functions to estimate the effective point-count duration in 6 different Chilean forests.  An effective point-count duration was dependent upon forest habitat, the type of accumulation function, and travel time.  The effective count durations predicted by 2 different species accumulation functions, the linear dependence and Clench models, increased with increasing travel time.  For short travel times (≤ 10 min), effective count durations were ≤ 5 min and slightly shorter than count durations required to reach 80% of the function asymptote.  For long travel times (20-30 min), effective count durations were about 7 min, but shorter than count durations required to reach 90% of the function asymptote.  These results show that for travel times of 5 min, the use of effective count durations can result in 50% more points.  Effective count durations are suggested when a survey is focused on assessing species richness and the presence of common or conspicuous species.