The effect of weather conditions on the feeding behaviour of a diving bird, the Common Guillemot Uria aalge

A detailed investigation of the effects of weather conditions on the feedin g behaviour of a pursuit diving seabird, the Common Guillemot Uria aalge, w as carried out during the chick-rearing period at a colony in southeast Sco tland in 1997. There was no evidence that the rate at which adults brought back fish for their chicks was related to weather conditions but the type o f prey delivered was affected with birds bringing in smaller sandeels Ammod ytes marinus in stormy weather. This resulted in a significant decrease in the mean energy value of a prey load and in the overall rate of energy inta ke of chicks. The attendance behaviour of adults also varied in response to the prevailing weather conditions. The proportion of sites with chicks whi ch had both adults present was significantly lower in stormy conditions ind icating that, although the frequency at which Common Guillemots provisioned their chicks was not affected, birds were spending longer away foraging. F urthermore, information on diving behaviour collected using radio telemetry suggested that birds were working harder when conditions were bad with the number of dives in a bout, and hence the amount of time spent underwater, increasing significantly and the interval between consecutive diving bouts decreasing significantly. Analysis of long-term data on chick provisioning and adult attendance for the study colony indicated that the observed reduc tions in the mean energy value of loads and the proportion of chicks attend ed by both adults in stormy weather, which were evident in the 1997 data, w ere also apparent across years. If the current climate change prediction of an increase in the frequency and/or intensity of storms at mid to high lat itudes proves correct, such trends could have marked energetic consequences for Common Guillemots in terms of increased foraging costs of adults and r educed energy intake of chicks.