Opvallend late wegtrek van Gierzwaluwen in 1978
Het Vogeljaar , Volume 28 - Issue 2 p. 57- 61
In the late summer of 1978 it appeared the Swift (Apus apus) stayed unusually long in the Netherlands. While the main force uses to leave in the first half of August, it was rather common throughout September. In Oktober there were at least 47 observations. The different behaviour must be due to the weatherconditions during the summer which was cold, dreary en rather wet. This must have lead to a greater inactivity of the flying insects by which the build up of the necessary reserves for the migration was delayed. The same applies to the breeding-period which can be extended to four weeks when the adult birds need more time to feed. Moreover the raising up of the juveniles can vary from five to eight weeks for the same reason. In Falsterbo (Sweden) the Swifts departed on schedule. Near Copenhagen (Danmark) however hundreds of birds were still seen in the first decade of Oktober. Late Swifts were also reported from Belgium.
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