Year-round used large communal roosts of Black-billed Magpie Pica pica in an urban habitat

Ientile R.

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Five roosts of Eurasian Magpie Pica pica have been studied in Siracusa city (Sicily, Italy). One of the roosts was monitored periodically, for a total of 34 visits. All these communal roost was used all year round, although the highest densities were detected during the non-breeding season. The following environmental characteristics of the wooded areas used as night roosts were registered: the location and the extent and composition of vegetation. Roosts features suggest an active preference for areas with a favourable microclimate during the cold season; Black-billed Magpies avoided north exposed areas as well as deciduous trees; on the other hand they selected safe areas (i.e. with scarce or no human presence). Significant correlations have been found between the mean daily temperatures and roost arrival time. In particular, roost arrival times are delayed during the coldest days, likely due to extended feeding activities. Significant correlations have also been found between the number of birds in the roosts and day length, temperature and wind speed. The data suggest that night roosting aggregations are influenced by environmental variables; long, cold and windy nights induce the birds flocking together, possibly also to reduce individual predation risk. At the same time, roosting behaviour could be advantageous at an individual level because these aggregations enable intraspecific interactions.