Abstract
To what degree juvenile migrant birds are able to correct for orientation errors or wind drift is still largely unknown. We studied the orientation of passerines on the Faroe Islands far off the normal migration routes of European migrants. The ability to compensate for displacement was tested in naturally occurring vagrants presumably displaced by wind and in birds experimentally displaced 1100 km from Denmark to the Faroes. The orientation was studied in orientation cages as well as in the free-flying birds after release by tracking departures using small radio transmitters. Both the naturally displaced and the experimentally displaced birds oriented in more easterly directions on the Faroes than was observed in Denmark prior to displacement. This pattern was even more pronounced in departure directions, perhaps because of wind influence. The clear directional compensation found even in experimentally displaced birds indicates that first-year birds can also possess the ability to correct for displacement in some circumstances, possibly involving either some primitive form of true navigation, or ‘sign posts’, but the cues used for this are highly speculative. We also found some indications of differences between species in the reaction to displacement. Such differences might be involved in the diversity of results reported in displacement studies so far.
Highlights
IntroductionThere is strong evidence that migratory birds inherit an endogenous directional programme, steering inexperienced migrants in a certain direction for a certain period of time [1,2]
There is strong evidence that migratory birds inherit an endogenous directional programme, steering inexperienced migrants in a certain direction for a certain period of time [1,2]. This programme alone does not enable migrants to navigate toward their unknown species-specific wintering grounds and it does not allow birds to compensate for a displacement [3]. This programme develops into a goal area navigation programme allowing the birds to accurately pin-point at least their breeding and winter grounds
Juvenile birds tested in Emlen funnels in Denmark were oriented toward southwest (a = 236u, r = 0.544, N = 29, P,0.001, Rayleigh test; Figure 1b) similar to the normal migration direction as found from ring recoveries (P.0.7, Watson-Williams test)
Summary
There is strong evidence that migratory birds inherit an endogenous directional programme, steering inexperienced migrants in a certain direction for a certain period of time [1,2] This programme alone does not enable migrants to navigate toward their unknown species-specific wintering grounds and it does not allow birds to compensate for a displacement [3]. With experience, this programme develops into a goal area navigation programme allowing the birds to accurately pin-point at least their breeding and winter grounds. There are no theoretical objections to juvenile migrants being able to correct for displacements: Juveniles could correct by using experienced-based navigating toward a site already visited on migration, as birds already on the way on their first migration could be acquiring information necessary for later navigation
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