Further studies on the stellar orientation of nocturnally migrating birds

Abstract

The discussion of the previously published experiments on the star-orientation of Lesser Whitethroats, Blackcaps, and Garden Warblers confirms the findings, that these nocturnal migrants, possessing an internal clock, rely on a spherical grid of two celestial coordinates. It still has to be analysed if these birds would refer to the azimuth and altitude of their stellar orientation pattern with the natural or an artificial horizon as the primitive circle. They also could make use of the second spherical grid with hour angle and declination, and the celestial equator as the circle of reference. There is no indication that the birds would rely on a star-compass alone. The system of orientation with two stellar coordinates is sufficient for nocturnal homing after displacements, as they were simulated in planetarium experiments. Some general remarks were made regarding migration orientation and homing abilities of displaced birds. In relation to this celestial orientation and the setting of the internal clock a possible establishment of a newly expanded species in a new geographical area is briefly discussed.