Point count duration: five minutes are usually sufficient to model the distribution of bird species and to study the structure of communities for a French landscape

摘要

The point count method is very widely used for estimating bird abundances. In studies of bird environment relationships, the duration used for point counts varies considerably from one study to another. Short counting times may increase the number of false absences while long counting times increase the probability that birds initially absent immigrate during the counting period. This study aims to quantify the effect of point count duration on the performance of bird distribution models and on the estimated structure of the communities. We used a sample of 256 point counts collected in south western France and we compared four count durations (5, 10, 15 and 20 min). After comparing the predictive performance of seven statistical methods, we constructed one GAM (generalized additive model) per counting time to link the presence absence data of each species with seven landscape variables. We evaluated the models by examining explained deviance and by comparing predicted and observed values for an independent data using AUC (area under the curve) and TSS (true skill statistics). At the community level, we constructed one CQO (constrained quadratic ordination) per counting time, then we compared the species' scores along the latent environmental variables. For the 21 species studied, the overall performance of GAMs only improves very moderately with a lengthening of the counting time (mean D-2 = 25% for 5 min and 28% for 20 min; mean TSS = 0.40 for 5 min and 0.43 for 20 min), with an increase for some species and a decrease for others. The latent environmental variables of the four CQOs were associated with the same explanatory variables and the scores of the species along the latent variables were highly correlated (between 5 and 20 min, P < 2.10(-16), rho = 0.99). In the perspective of building reliable bird distribution models, our results thus show that a point count duration of 5 min is sufficient in temperate regions such as France.