Newson, S.E., Hughes, B., Hearn, R. & Bregnballe, T. 2005. Breeding performance and timing of breeding of inland and coastal breeding Cormorants Phalacrocorax carbo in England and Wales. Bird Study 52 (1),
10-17.

Summary

Aims To compare breeding performance of inland and coastal breeding Cormorants in England and Wales and to provide breeding performance data for Cormorants for future demographic studies.

Methods Breeding performance and timing of breeding was monitored at six inland and four coastal colonies during 1997 and 1998. We compare clutch and brood size and egg and nestling survival.

Results Breeding performance was higher at inland colonies because of higher nestling survival during the later stages of nestling development, from 15-56 days.

Conclusions Greater and earlier food availability at inland colonies, resulting in earlier and more protracted breeding is the most likely explanation for differences in breeding performance. A more protracted breeding season would reduce competition for food and enhance breeding performance, which may be especially apparent during late chick development when energy demands are greatest.

Key words : Phalacrocorax carbo - Great Cormorant – breeding performance – timing of breeding – Mayfield estimates