Modelling migration: the clock-and-compass model can explain the distribution of ringing recoveries.

The aim of the present study was to test whether the directional distributions found in ringing recoveries could be explained if night-migrating passerines use only a simple clock-and-compass strategy during autumn migration. I developed a mathematical model that predicts the expected directional distributions as a function of distance covered by birds using a clock-and-compass strategy. The predictions were compared with data from natural migration: all ringing recoveries of pied flycatchers, Ficedula hypoleuca, ringed in Scandinavia and recovered elsewhere in Europe and North Africa within the same autumn. The predictions of the model correlated strongly with the distribution of ringing recoveries. This suggests that at least young pied flycatchers, and perhaps night-migrating passerines in general, use a simple clock-and-compass strategy to reach their wintering area. If so, all the prerequisites (a compass and an internal clock) that they need to orient during migration seem to be known at present, at least at the behavioural level, and navigational abilities or any elusive map-sense are not needed for migration. Copyright 1998 The Association for the Study of Animal Behaviour.