Estimation of Feral Pigeon (Columba livia) population size using a novel Superimposed Urban Strata (SUS) method

Abstract

A reference method to estimate Feral Pigeon (C. livia) population size in urban areas is missing: results of different surveys are difficult to compare due to the wide heterogeneity of approaches. A combined technique, the Superimposed Urban Strata (SUS) method, especially designed to estimate pigeon population size in urban areas, is proposed. SUS implements methods based on stratified sampling layers: its reliability was tested with a pilot study in Padua (Italy). The survey area was split into two superimposed strata and a different survey technique was applied to each stratum. The first stratum consisted of twelve topographic sampling units, identified as critical ornithic-density loci. The second stratum was obtained by selecting 10 % of the survey area with systematic sampling. In the estimate of the population size, different detection probabilities were assigned to the two strata. The SUS method was first applied in 2007, when three-year growth projections for the C. livia population were calculated, with a density-dependent model. In 2010, the survey was repeated to countercheck previous data. Estimated C. livia population size was of 2340 ±93 units in 2007, whereas in 2010 it was of 3679 ±161 units. The 2010 estimated population size resulted in fair accordance with the three-year projections, showing less than a 4 % mismatch. SUS proved to be an adequate estimate method for urban areas: so far it has been tested only in an average Italian urban area, but it could be easily adapted to other cities by calibrating parameters linked to the peculiar urban background.