7 THESES ON PIGEON HOMING DEDUCED FROM EMPIRICAL-FINDINGS

Experimental findings obtained in recent gears make it possible to rec ognize and distinguish the most relevant components determining homing flights of displaced pigeons. Conclusions deduced from these experime nts, more or less compelling or tentative, are presented in the form o f seven theses, supplemented by several subtheses along with reference to empirical data. The principal theses are as follows. (1) Passively displaced pigeons find the way home by using location-dependent signa ls and not by path integration based on recording of motion. Pigeons a re able to home, even from unfamiliar areas, without access to potenti ally useful information during transport to the release site. (2) Home -related orientation of pigeons in unfamiliar areas requires positiona l information acquired olfactorily from atmospheric trace gases. Empir ically deduced details of olfactory navigation are enumerated (connect ion with winds and the sun, inaccuracy, spatial range, time course of sampling and memorizing spatial information, etc.). The critical gap i n our knowledge, i.e. the nature and spatio-temporal distribution of t he substances involved, is provisionally filled by speculation. (3) In familiar areas, known from previous flights, the visual landscape is used additionally to find the way home. (4) Initial orientation of pig eons does not exclusively reflect home-related navigation but includes components independent of the position with respect to home. Observed bearings are co-determined by a general preference for a certain comp ass direction and by distracting features of the nearby landscape. (5) Proportions among components controlling initial orientation accordin g to theses 2-4 are highly variable depending on local, temporal and e xperimental conditions and on the life histories of the pigeons. This complexity greatly restricts recognition of the navigationally relevan t components of behaviour at a given release site. (6) Sensory inputs, being neither olfactory nor visual, do not substantially contribute t o determining the current position with respect to home. This thesis n eed not be definitive, but at present no contradicting evidence is ava ilable. (7) Pigeon homing is a model case of bird homing in general. E xperiments with other species support this thesis. So far, there is no reason to assume that wild birds apply mechanisms fundamentally diffe rent from those of pigeons to find the way home.