EXAMINING THE LIMITS OF FLIGHT AND ORIENTATION PERFORMANCE - SATELLITE TRACKING OF BRENT GEESE MIGRATING ACROSS THE GREENLAND ICE-CAP

Brent geese, Branta bernicla hrota, were equipped with satellite trans mitters on a spring stop-over site in Iceland. The brent geese deposit heavy fuel reserves for long-distance flights across the high Greenla nd ice-cap to breeding destinations in north Canada. Satellite trackin g of brent geese on this journey serves the twofold purpose of testing specific predictions about: (i) size-dependent power constraints in b ird flight (severe restrictions in climbing capacity with heavy payloa ds); and (ii) orientation constraints at northerly geographic and magn etic latitudes (different routes depending on which celestial or geoma gnetic cues are used). Five individuals were successfully tracked to w est Greenland, and they traversed the Greenland ice-cap where it reach es > 2500 m above sea level (ASL). Their climbing rates were exceeding ly small, 0.01-0.06 m s(-1), indicating critical size-dependent power limitations on flight. The movement up the ice slope was very slow, an d the most plausible interpretation is that the geese paused frequentl y between partly anaerobic flights. The flight tracks were surprisingl y irregular, although departure directions from Iceland and across Gre enland were similar. The geese's orientation is probably based on a co mbination of landmark piloting and a compass mechanism giving a consta nt geographic course irrespective of longitudinal time and geomagnetic declination (variation) differences along the route.