|
Résumé :
|
By computer simulations of different Eight routes for spring migrating Knots Calidris canutus, potential orientational 'danger zones' were revealed in the equator area and north of the Arctic circle. An evaluation of the availability of directional information during migratory flights demonstrated the potential hazards of crossing these danger zones. Investigations of the directional consequences of sun compass orientation based upon an internal clock in phase with local time at the departure site showed that such a mechanism would entail serious losses in distance and time. A simple-compensating rule based. on th rare of change in sun altitude was found to worts well both at polar latitudes and in the equator area. The magnetic compass will become inoperative close to the magnetic equator and the poles, thus restricting the availability of directional information. Orientation by stellar cues will become impossible during spring and summer at arctic latitudes. Simulations of potential migratory routes also enabled examination of the required precision of compass systems and it was indicated that necessary orientation accuracy requires more than one directional selection per long-distance flight to ensure survival. It is concluded that computer simulations of Right tracks, based on ringing recoveries, visual observations, radar studies and satellite telemetry maybe a powerful tool helping to identify problems which require future experimental attention.
|