Movement of Breeding Birds May Create Bias in Abundance Estimates

Movement of birds within a breeding season may be a substantial source of bias in estimates of their abundance, according to recently published research funded in part by SW CASC. The authors used both simulated data on breeding birds and data from point-counts of breeding birds conducted in the Great Basin to evaluate an assumption of many occupancy models—that individual animals are present throughout the survey season. Their results suggested that movement between surveys was common in their study system, and that the magnitude of bias in estimates of abundance was affected by how abundance was defined. However, in most situations, movement did not affect inferences about associations between abundance and environmental attributes.