Gap crossing decisions by reed warblers (Acrocephalus scirpaceus)in agricultural landscapes

To meet the need for research on the requirements for corridors for marshland birds, this study set out toquantify gap crossing decisions made by reed warblers moving through the landscape. In three experiments,reed warblers were released into landscape situations with di?erent gap sizes and their movement towardsreed patches fringing a watercourse were monitored. In all experiments, most birds ?ew over the smallestgap towards the nearest reed patch. In the experiment with two gap sizes, the probability of crossing a gapwas a function of the ratio between distances to the reed patches. In the experiment with increasing gapsizes, most birds crossed the smaller gaps frequently. Near the bigger gaps, birds did not cross the gaps;instead, they only crossed the watercourse repeatedly. In the third experiment with more realistic landscapecon?gurations, the birds preferred nearby non-reed landscape elements to more distant reed patches. It isconcluded that reed warblers were reluctant to cross gaps wider than 50 m. The results suggest that thepresence and size of gaps in reed patches a?ect reed warblers’ local gap-crossing decisions: when given achoice, the birds prefer to cross the smallest gap. Furthermore, reed warblers may be directed towardssuitable marshlands by creating corridors of reed vegetation with gaps no wider than 50 m. The surroundingagricultural landscape and the presence of trees and ditches could decrease the reluctance to crossgaps in corridors.

L. Bosschieter and P.W. Goedhart, Landscape Ecology (2005) 20: 455-468