Orientation and long-distance migration routes: an attempt to evaluate compass cue limitations and required precision

By computer simulations of different Eight routes for spring migrating Knot s Calidris canutus, potential orientational 'danger zones' were revealed in the equator area and north of the Arctic circle. An evaluation of the avai lability of directional information during migratory flights demonstrated t he 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 mec hanism would entail serious losses in distance and time. A simple-compensat ing rule based. on th rare of change in sun altitude was found to worts wel l both at polar latitudes and in the equator area. The magnetic compass wil l become inoperative close to the magnetic equator and the poles, thus rest ricting 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 r equired precision of compass systems and it was indicated that necessary or ientation accuracy requires more than one directional selection per long-di stance flight to ensure survival. It is concluded that computer simulations of Right tracks, based on ringing recoveries, visual observations, radar s tudies and satellite telemetry maybe a powerful tool helping to identify pr oblems which require future experimental attention.