Breeding Dispersal

One of the earliest findings to emerge from bird-ringing was that, once individuals had bred in an area, they tended to stay there, or to return there to breed year after year. Individuals were found to occupy the same territories in successive years, or to move to other territories nearby. In many species of seabirds and raptors, individuals often returned to exactly the same nest-sites.

Site-fidelity of adult birds has been shown mostly in specific study areas, by counting the proportion of marked individuals present in one year that returned the next. On this basis, any birds that moved outside the area would be missed, and the smaller the area the lower the expected return rate, as explained above. Nevertheless, in some species the proportion returning to particular areas was so high that, allowing for known mortality rates, few if any individuals could have moved elsewhere (Figures 17.3 and 17.4, Table 17.1). To judge from general ring recoveries, the settling pattern in breeding dispersal shows a similar dartboard pattern to natal dispersal, but over shorter distances (e.g. Table 17.2; Jackson

Eurasian Sparrowhawk Accipiter nisus (Newton & Rothery 2000), Northern Goshawk Accipiter gentilis (Byholm et al. 2003), Common Kestrel Falco tinnunculus (Village 1990), and Western Gull Larus occidentalis (Spear et al. 1998).

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