Food supply and dispersal in the determination of wintering population levels of oystercatchers, Haematopus ostralegus

Abstract

A considerable cockle spatfall in 1975 led to a dramatic, short-lived increasein the cockle population on the Ribble Estuary. There was a parallel fluctuation in the numbers of oystercatchers. The correlation between the two was high. This study contrasts with that on the Burry Inlet where the numbers ofoystercatchers did not vary greatly with the number of cockles. It appears that dispersal is an important factor determining the number of birds on the Ribble, yet other population processes appear to affect the Burry Inlet oystercatchers. Much of the increase in the oystercatcher numbers on the Ribble was due to the immigration of young birds. It appears that young birds seek a suitable estuary whilst adults tend to return to the one found whilst young.