Life-History Strategy of the Herring Gull: Changes in Survival and Fecundity in a Population Subjected to Various Feeding Conditions

Abstract

The present study compares breeding parameters and adult survival rate in a herring gull colony before and after the closing of a large refuse tip where breeders used to find most of their food. During the first study period (1983-88) food of human origin was abundant and virtually always available. During the second period (1989-90) such food was scarce. The annual adult survival rate was time-dependent. It varied from 0.826 (SE = 0.031) in 1987-88 to 0.975 (SE = 0.022) in 1985-86. The average survival rate calculated for 1983-90 was 0.881 (SE = 0.014). There was no significant difference in adult survival between males and females. The closure of the refuse tip was not followed by a significant decrease in adult survival rate. After the refuse tip was closed, mean clutch size and mean production of young per breeding pair decreased by 6.7% and 49.1%, respectively. Mean adult body weight decreased by 4.6% for males and by 4.7% for females. The proportion of non-breeders among former breeders and the proportion of 3- and 4-year-old individuals among ringed birds did not change after closure of the tip. The results are discussed in terms of the life-history theory, which predicts that in long-lived species a decrease in food supply should affect fecundity before affecting adult survival.