Examining the limits of flight and orientation performance: satellite tracking of brent geese migrating across the Greenland ice-cap

Abstract

Brent geese, Branta bernicla hrota , were equipped with satellite transmitters on a spring stop-over site in Iceland. The brent geese deposit heavy fuel reserves for long-distance flights across the high Greenland ice-cap to breeding destinations in north Canada. Satellite tracking of brent geese on this journey serves the twofold purpose of testing specific predictions about: (i) size-dependent power constraints in bird flight (severe restrictions in climbing capacity with heavy payloads); and (ii) orientation constraints at northerly geographic and magnetic latitudes (different routes depending on which celestial or geomagnetic cues are used). Five individuals were successfully tracked to west Greenland, and they traversed the Greenland ice-cap where it reaches > 2500 m above sea level (ASI). Their climbing rates were exceedingly 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, and the most plausible interpretation is that the geese paused frequently between partly anaerobic flights. The flight tracks were surprisingly irregular, although departure directions from Iceland and across Greenland were similar. The geese’s orientation is probably based on a combination of landmark piloting and a compass mechanism giving a constant geographic course irrespective of longitudinal time and geomagnetic declination (variation) differences along the route.