Seasonal Changes in Ranging Behaviour and Territoriality in the European Jay Garrulus g. glandarius

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Abstract
This 5-yr study analyses home-range sizes in a population of European Jays in southernmost Sweden in relation to population density and breeder status. Home-range sizes were measured by radio-tracking during the pre-breeding and breeding periods. The home-range sizes of individual Jays changed with the onset of breeding. In years with a high number of adult birds at the beginning of the breeding season, home-ranges were compressed and, conversely, during low density years they were enlarged. Whereas home-range size was positively related to population density during the pre-breeding period, it showed a negative relative to density during breeding. Non-breeders had larger home-ranges than breeders at all breeding population densities. Intrusions by neighbours were more frequent during pre-breeding. These results suggest that an increase in territorial behaviour by resident Jays occurs during the breeding period, probably owing to increased competition over resources important to reproduction.