Distance sampling as an effective method for monitoring 5 feral pigeon ( Columba livia f . domestica ) 6 urban populations 7

13 Abstract Current methods for estimating feral pigeon (Columba livia) population size and 14 for monitoring population trends are mainly based on indices, which according to the 15 current literature on wildlife census methods often produce biased results. Distance 16 Sampling techniques have never been used in this context, even though they could 17 theoretically produce absolute abundance estimates at relatively low costs. The aim of this 18 paper was to investigate the performance of Distance Sampling to census feral pigeons, and 19 to compare these results with those obtained by using Quadrate Counts, a widespread 20 method for monitoring these birds. Surveys were performed in Pisa (Italy) in two different 21 periods of the year 2004 (end of January–beginning of February, and November), which 22 correspond to a minimum (January–February) and a maximum (November) numbers for 23 pigeon populations. We conducted 40 line transects each about 250 m long for Distance 24 Sampling, and 40 250×250 m cells for Quadrate Counts. In both cases, sampling units were 25 randomized in a stratified design. In contrast to Quadrate Counts, Distance Sampling 26 detected the predicted increase of abundance from January–February to November with an 27 acceptable precision and no increase of costs per survey. Even though the possible biases 28 (due to the not rigorously random distribution of transects and to the spiked nature of 29 collected distances) should be further investigated, results suggest that Distance Sampling is 30 a viable and efficient alternative to the traditional methods used to estimate feral pigeons 31 population size and to monitor trends.