Behaviour and Physiology of Svalbard Barnacle Geese Branta leucopsis during Their Autumn Migration

Abstract

Few studies of flight physiology have used birds that are in the migratory state. Thus, we obtained behavioural and physiological data from a group of Svalbard Barnacle Geese before and during the autumn migration from their breeding area around Ny-Alesund (790N) to their wintering grounds around the Solway Firth, Scotland (550N). We attached lightweight (33 g) satellite transmitters (PTTs) to some birds in order to determine their behaviour, and implanted small (20 g) data loggers into the abdominal cavity of other birds to obtain some indication of their energy expenditure during migration. The maximum single non-stop flight duration was approximately 14 h and all the geese flew along the Norwegian coast, with a number of stops en route. All birds showed impressively long bouts of flight with little opportunity for significant refuelling, with one bird flying for 49 h out of a possible total time of 59 h. Thus, from the perspective of taking on fuel, these periods of flight could be considered as being physiologically non-stop. Average heart rate at the beginning of migration was 317 beats min - ' and declined to 226 beats min - ' towards the end, giving a calculated scaling exponent for estimated oxygen consumption of 1.46 with respect to estimated body mass (M1.46). Heart rates of 512 beats min -' have been recorded from Barnacle Geese flying behind a truck (Butler and Woakes 1980). Thus, the sub-maximal values of heart rate recorded during the autumn migration indicate that the energy cost of migratory flight is likely to be somewhat less than that previously assumed. Heart rate appears to be the major functional cardiovascular variable that is adjusted during flight with respect to changes in energy requirements. It is estimated that, depending on the oxygen carrying capacity of the blood and on the ability of the tissues to extract oxygen, the minimum rate of oxygen consumption of a 2.3 kg Barnacle Goose at the beginning of the migration is approximately 300 ml min -' (which is equivalent to around 100 W).