The effect of artificial chick shelters on nest placement by Common Terns Sterna hirundo

Capsule The density of Common Tern Sterna hirundo nests on artificial islands was increased by the provision of chick shelters, which influenced the placement of nests. Aims To understand the nest placement behaviour underlying the distribution of Common Tern nests on artificial islands with and without chick shelters. Methods We studied Common Tern nest placement patterns on an artificial island in an inland pond in Germany where ridge tiles had been deployed as chick shelters. We used point process statistics, taking the nest locations as points. The pattern of nest placement was compared with simulated patterns without chick shelters: (a) a pattern derived by replacing the nest clusters around tiles in the observed pattern with single nests and (b) patterns derived from a statistical model describing nest patterns without chick shelters from a region close to the German North Sea. Results The density of nests in close proximity to ridge tiles was higher than elsewhere on the artificial island. This suggests that the presence of tiles reduced the inter-nest distances that are acceptable to breeding Common Terns. The assumed pattern without nest clusters is shown to be similar to modelled patterns based on tern colonies without chick shelters. The presence of chick shelters appears to have resulted in a 16% increase in nest density. Conclusions Chick shelters such as ridge tiles can help to increase the numbers of breeding Common Tern pairs accommodated on artificial islands.