A methodological approach to feral pigeon (Columba livia) census in urban areas

Correction coefficients (CCs) are used to improve censuses of Feral Pigeons, Columba livia, within large urban areas, because most of individuals are not directly visible. However, a satisfactory analysis of procedures of quantifying CCs has not been thoroughly addressed. In this study we investigated, by capture-recapture methods, the effects of structural heterogeneity of buildings, non complete closure of population, and heterogeneity in bird’s capture probability, on the procedure commonly used for the computation of CCs. Our results indicate that either heterogeneity of capture as structural features of different areas of the city differently affected pigeon sightability, and consequently CC values. Two main solutions might be applied: 1) using capture-recapture methods based on partial closure of population and heterogeneity of capture (e.g. the Bowden index) instead of the Petersen-Lincoln index, and 2) sampling more than one site in order to remove the effects of structural variability of buildings.