For each prey species, at least one variable explained a significant proportion of sample variation and was significantly related to the mass. Usually, cranial bones in pellets are severely damaged and the number of feasible measurements is limited, therefore multiple regression methods based on several variables are of limited use. The most coherent explanation for the difference in vigilance level between peripherally and centrally foraging Dunlins is the individual birds perception of a higher predation risk when exposed. It is argued that vigilance for predators in Dunlins constrains foraging activity rather than vice versa. Hence, the adaptive significance of flocking in Dunlins may be an increased feeding activity without jeopardising predator surveillance.
Islands are, generally, inhabited by widespread and generalist bird species.
This phenomenon, well known in literature and here extended to a peninsular gradient, is confirmed in Italy for breeding landbirds, and for the sedentary ones, elaborating data of the Atlases. The mean range size values of the species are higher in all the studied islands compared to the mainland. The lesser the island area the higher is the mean range size of the species found. Stenotopic species, rare and localised, are present with lower frequency in small islands, the contrary occurs for widespread species. This may be explained, mainly, by the different orophysiographical and environmental availability which affect, at the same time, the bird richness and, in particular, the distribution of the rare and localised species.