NATAL DISPERSAL OF GREAT-TITS IN A PATCHY ENVIRONMENT

The importance of dispersal for population genetics, population dynami cs, and conservation biology is well established. We studied natal dis persal of Great Tits between Wytham Wood (high-quality habitat), and h edgerows and small woodlands within 2 km of Wytham Wood (the ''surroun ding area''; low-quality habitat). We (1) quantified the exchange of b irds between these habitats, and (2) evaluated whether there was pheno typic variation between dispersing and philopatric birds. Only 6% of i mmigrants in Wytham were born in the surrounding area, and only 5% of emigrant recruits from Wytham bred in the surrounding area. This indic ates that most nonphilopatric birds dispersed >2 km, considerably fart her than expected. The effect of sex on dispersal depends on the scale on which it is studied: females dispersed longer distances than males , but the exchange of birds between woodlands was not sex biased. The proportion of immigrants among breeding birds was similar for both sex es, confirming the latter result. Dispersing and philopatric birds did not differ in hatch date, but birds that hatched in the surrounding a rea and dispersed into Wytham had greater nestling mass than those tha t did not. This effect was not found in Wytham, suggesting that there is an interaction between phenotypic quality and habitat quality with respect to dispersal: birds of high phenotypic quality disperse when t hey are born in low-quality habitat. As a result, birds breeding in Wy tham (high-quality) had greater mass as nestlings than birds breeding in the surrounding area (low-quality). To our knowledge, this is the f irst demonstration that conditions during early development have an af fect on the quality of the environment in which a bird subsequently re produces.