Breeding densities of Robin Erithacus rubecula in different habitats: The importance of hedgerow structure

Abstract

Capsule: Territory density varied between habitat types and displayed a clear relationship with certain macro- and micro-habitat characteristics. Aims: To investigate the role of habitat and structural hedgerow components on breeding densities of Robins and to provide baseline territory density estimates for the Robin in a range of habitats in south-west Ireland. Methods: Robin territory densities were estimated at 39 sites of five major habitat types in southwest Ireland. A modified CBC-type technique was used to census Robins and additional habitat data were collected at each site. One-way ANOVA with post hoc testing was used to investigate the population densities between the different habitat groupings, and a principal component analysis of habitat data was used to generate independent variables for a stepwise regression where territory density per hectare and territory density per kilometre were, in turn, the dependent variables. Results: Population densities varied significantly between habitat types. The highest Robin territory densities were encountered in semi-improved grassland sites and the lowest values in suburban gardens. The mean territory density per hectare in all farmland habitats surveyed was notably higher than published estimates for British farmland and woodland. The quantity of hedgerow available appeared to be an important factor in determining Robin abundance on farmland. There was also a relationship between various hedgerow structural components and Robin territory density. Conclusion: Our analysis indicated that high bushy hedgerows with narrow banks and low basal vegetation positively influenced the number of Robin territories per hectare. We also conclude that if basal vegetation becomes overgrown at some critical point it impedes detection of prey by Robins, even when there are many available foraging perches. © 2006 British Trust for Ornithology.