Regional patterns in proportion of bird species detected in the North American Breeding Bird Survey

Counts from the North American Breeding Bird Survey (BBS) underestimate species richness. We use capture-recapture methods to estimate species richness from BBS count data collected in 1996 and show that detection probabilities demonstrate clear regional patterns. Capture-recapture methods should be used to estimate species richness from count data, and failure to use estimation procedures for species richness could result in biased estimates of spatial change in species richness.