Stay or go? Strong winter feeding site fidelity in small woodland passerines revealed by a homing experiment

Abstract

Many birds exhibit territoriality, which is vital for obtaining resources for survival. Non-migratory birds maintain larger territories in winter than during reproduction, but the degree of their fidelity to these winter home ranges is less well-known. We evaluated the homing success and time of return to home through a field experiment in which we trapped and displaced 1239 individual birds of two tit species, Great Tit (Parus major) and Blue Tit (Cyanistes caeruleus), and retrapped 267 of them over two winters (a total of 40 trapping sessions). Displacement of the birds between two sites 7.8 km apart revealed strong fidelity to the winter home range in both species; birds returned on average within 4 weeks. Greater homing success was found in Blue Tits than in Great Tits (45.7 vs. 32.5 % retraps). More individuals returned home from an ecotone site, which included gardens with feeders, than from a forest site (40.9 vs. 29.2 %). Blue Tits homed approximately 1 week more quickly than Great Tits, and similar mean differences were observed when comparing males with females of both species using Kaplar–Meier survival functions. A parametric survival regression model indicated that the difference in homing time between species was not significant, but males of both species returned significantly sooner than females. Moreover, birds that originated from a site with greater food supply homed more quickly, and interaction of sex and site also showed a significant effect in this model. Our evidence suggests that winter territoriality of these woodland passerines is shaped potentially by all tested factors and is an important behavioural characteristic linked with their ability to find limited resources during the harsh period of the year.