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Presumed hybrid Western Bonellis x Wood Warbler

Last Monday (14 May 2018) at about 07:45, I found a very interesting warbler at Noordhollands Duinreservaat, Castricum, the Netherlands. The first song phrases I heard were similar to Western Bonelli’s Warbler. But then the bird started singing another song type, including a few introductory notes as in Wood Warbler. A bit confused and thinking it was probably just an odd Wood Warbler, I tried to see what the bird looked like. As it was singing from a small patch of oak trees, using exposed song posts and flying between them at c 2-3 m above the ground, it did not take long to get proper views. Shocked by the fact that it also looked like a cross between the two species, the 'hybrid option' then seemed the only logical explanation. I decided it was time to inform other birders.

The bird was studied by several birdwatchers (for example, see here for Hans Schekkerman's clear observations and extensive description) and is still showing today (18 May). On the evening of 15 May, it was trapped and ringed by Tim van der Meer and Jan Visser. Biometrics were taken (for example, a wing length of 73 mm) and a feather was collected for DNA analysis. Obviously I am very much looking forward to seeing the results!

To be continued...




hybrid Western Bonelli's x Wood Warbler

hybrid Western Bonelli's x Wood Warbler

hybrid Western Bonelli's x Wood Warbler

hybrid Western Bonelli's x Wood Warbler

hybrid Western Bonelli's x Wood Warbler

hybrid Western Bonelli's x Wood Warbler

Song type 1 (three variants were recorded) is most similar to Western Bonellis. Click here to listen to the recording; the sonagram shows the first song phrase.

hybrid Western Bonelli's x Wood Warbler

Song type 2 is most similar to Wood Warbler. Note also the two introductory notes similar to Wood Warbler. Click here to listen to the recording; the sonagram shows the seventh song phrase.

hybrid Western Bonelli's x Wood Warbler

This call type (between the introductory notes and the song phrase) is most similar to Western Bonellis Warbler. Click here to listen to the recording.


PS, what happened later that morning on 14 May is described here... A memorable day it was!


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Published 18 May 2018