Behaviour and physiology of Svalbard Barnacle Geese Branta leucopsis during their autumn migration

Few studies of Night physiology have used birds that are in the migratory s tate. Thug we obtained behavioural and physiological data from a group of S valbard Barnacle Geese before and during the autumn migration from their br eeding area around Ny-Alesund (79 degrees N) to their wintering grounds aro und the Solway Firth, Scotland (55 degrees N). 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 cavi ty of other birds to obtain some indication of their energy expenditure, du ring migration. The maximum single non-stop flight duration was approximate ly 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 Eight with litt le opportunity for significant refuelling, with one bird Eying for 49 h out of a possible total time of 59 h. Thus, from the perspective of laking on fuel, these periods of Eight could be considered as being "physiologically" non-stop. Average heart rate at the beginning of migration was 317 beats m in(-1) and declined to 226 beats min(-1) towards the end, giving a calculat ed scaling exponent for estimated oxygen consumption of 1.46 with respect t o estimated body mass (M-1.46). Heart rates of 512 beats min(-1) 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 mig ration indicate that the energy cost of migratory flight is likely Co be so mewhat less than that previously assumed. Heart rate appears to be the majo r functional cardiovascular variable that is adjusted during Eight with res pect 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 Barn acle Goose at the beginning of the migration is approximately 300 mi min(-1 ) (which is equivalent to around 100 W).