Anosmic migrating songbirds demonstrate a compensatory response following long-distance translocation: a radio-tracking study

A number of studies have shown that migrating birds can navigate to their destinations even when displaced to unfamiliar territory. It has been demonstrated that adult Eurasian reed warblers, (Acrocephalus scirpacues), captured in spring in the Eastern Baltic, displaced 1,000 km eastward to the Moscow region and tested in orientation cages, show a clear orientation tendency towards their breeding grounds. This response requires the ability to determine a new geographic position relative to the goal. The natural cues that are used as coordinates for this behaviour remain controversial. Among other natural cues, both magnetic and olfactory sources of information have received the most experimental attention. More recently, virtual displacement experiments have shown that the geomagnetic information alone is sufficient for reed warblers to find their geographic position. However, the role of olfaction was not explicitly examined. In the present study, we displaced anosmic reed warblers together with untreated controls between the same capture and displacement sites where the Emlen funnel tests were previously performed. Following release, we radio-tracked birds for the first few kilometres using an array of automated radio tracking towers. The result strongly suggests a navigational response of both anosmic and intact birds (anticlockwise re-orientation), unlike some other experiments showing impaired navigational abilities of anosmic migrating birds. This data supports the hypothesis that, at least in this songbird species, the olfactory system is not crucial for determining geographic position and the Zinc Sulphate anosmia treatment is unlikely to have any non-specific effects on navigational abilities.