Influence of point-of-departure climate variables on the passage dates of two long-distance migrants in Eilat

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We examined the influence of point-of-departure climatic variables in autumn, namely surface ambient temperature, the number of wet days and growing season length (GSL), and the influence of the point-of-departure surface ambient temperature in spring on the passage dates of 2 long-distance migrant passerine species, the lesser whitethroat Sylvia curruca and the bluethroat Luscinia svecica, at Eilat, Israel, from 1985 to 2004. Ambient temperature at the breeding grounds of the lesser whitethroat increased at a rate of 0.147°C yr -1 . There was no significant change in the ambient temperature at the breeding grounds of bluethroat, nor was there a change in the number of wet days or GSL at the breeding grounds of either species. We found that the median autumn pas- sage date of lesser whitethroat in Eilat was delayed by 21.5 d, or by 5.43 d for every 1°C increase in ambient temperature at their breeding grounds. We found no change in the median autumn passage date of bluethroat in Eilat. The median spring passage date and the ambient temperature at the win- tering grounds of both species did not change significantly. We found no significant correlation between the median spring passage dates of birds of either species and the ambient temperature at their wintering grounds. We conclude that migration phenology of long-distance migrants can be strongly correlated with fluctuations in climatic variables, especially the ambient temperature at the breeding grounds of a species.