Structure of tree vegetation may reduce costs of territory defence in Eurasian Nuthatch Sitta europaea

Abstract

Capsule In pastured old oak woodland, breeding pairs of Eurasian Nuthatch selected territories with significantly higher densities of trees and cavities.Aims To define territorial borders that exist within a nuthatch population and to compare densities of trees and cavities between used and non-used parts of their available habitat in order to determine habitat preferences.Methods The number and location of territories was estimated by mapping the individual positions of colour-ringed birds. We measured habitat characteristics in regular sampling grid (number of trees and number of cavities per 50 × 50 m) during three successive seasons and modelled probability of occurrence of nuthatch territories in the area.Results Breeding pairs were observed to defend territories of median size between 1.46 and 2.93 ha. These sizes correspond well to high-quality habitat territories for this species. We found that pairs tended to occupy territories with higher densities of trees and cavities. Based on generalized linear mixed-effects model estimates, we found that in pastured oak woodland habitat with density of 60 trees per ha, the estimated probability of occurrence (with 95% confidence interval) of a nuthatch territory was about 96% (83−99). For cavity density, the probability of territory occurrence was about 74% (52−89) at the level of 60 cavities per ha.Conclusion We suggest that higher tree and cavity densities reduce territory defence costs in the species because birds may use less energy during foraging, predation avoidance and competition for a nest hole.