Connectivity in Reed Warblers Acrocephalus scirpaceus between breeding grounds in Europe and autumn stopover sites in Iberia

Abstract:
We determined the degree of connectivity in the Eurasian Reed Warbler

Acrocephalus scirpaceus between breeding regions in central and northern

Europe and stopover sites in Iberia, during the autumn migration. We used both

recovery data and wing length analyses to achieve this. Biometric data were

obtained during 2009 at 11 sampling localities in Iberia, which we amalgamated

into four major migratory areas within the region (Central, Western, Eastern

and Southwestern Iberia, hereafter CI, WI, EI, SW). From the EURING database,

we selected birds captured at their breeding sites in Europe and recaptured

in Iberia during the autumn migration. Reed Warblers passing through WI

had shorter wings than those in CI, EI and SW, suggesting that birds in WI

migrated shorter distances, a fact also supported by recovery data. Although

Reed Warblers showed some population overlap when passing through Iberia,

we found that birds passing through EI and CI came from areas further to the

east (continental Europe) than those passing through WI (mainly British Isles),

thus supporting parallel migration. Reed Warblers tended to converge in southwestern

Iberia, suggesting an effect of nearby geographical barriers.