Bird migration is usually performed in several
consecutive flights, interrupted by stopovers when birds rest or replenish
their fuel loads. As a
result, migrants must decide when and where to land. Here, we studied the effects of meteorological
conditions (wind and rain) and age (used here as a indicator of bird
experience) on the probabilities of sedge warblers Acrocephalus schoenobaenus landing at a stopover site in northern Iberia.
Data were collected over three consecutive years at a ringing station during
the autumn migration period. We used reverse-time capture-mark-recapture models
to estimate seniority, ? (i.e., the
probability that an individual at time t
was already present in the population at time t - 1), as an indicator of landing decisions, since 1- ? represents
the probability of recording new individuals (i.e. recent landings). We ran 14 models with the above mentioned
variables, four of which were best supported by the data. In these, only rain
showed a significant positive effect on ?, indicating that birds of any age
class avoid flying during rainfall and prefer to interrupt their migration.
These results are similar to those obtained from an analysis of day-to-day
variation in first captures that was used to validate the usefulness of
capture-mark-recapture models. They suggest that CMR models can serve to study
bird landing decisions during migration in some specific cases.
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