Observations on desertion and recruitment in a population of breeding Common Sandpipers Actitis hypoleucos at the edge of their range

摘要

More than thirty years of watching colour-ringed Common Sandpipers leads us to consider what attracts a recruit to join a population or a previous member to desert it. Experienced males reclaim their breeding territory when they return and experienced females join them almost immediately. New males arrive later, and we suggest that they judge the area by the behaviour of the birds already present. If there is a group of males vigorously displaying and attracting females, then the area is well-worth settling in unless it is so crowded that all possible territories are taken up. However, if there is an inadequate level of activity, even a returning male may desert an area. At the end of the season, males may make some reconnaissance of other sites. When a breeding range contracts, a self-reinforcing decline can take place at sites around the edge with reduced settlement of recruits and desertion by previous occupants.