24 August 2015

Why so many adult Sedge Warblers?

We've noticed this month that we seem to have been catching more adult Sedge Warbles than normal, so we thought we'd have a look back through our data from previous years and see if this is correct... So we compared the percentage of adults in our reedbed catches at Marazion/Gunwalloe and also at the migration site at Nanjizal.

We couldn't find a photo of adult/juvenile Sedge Warblers side by side,
so this wing shot of will have to suffice,
but the difference in wear on the flight feathers is obvious,
hence these birds are easy to age
 So the August percentages look like this (with total number of birds caught in brackets)...

Gunwalloe/Marazion Nanjizal
2011 10% (375)
2012 16% (125)
2013 8% (198) 7% (215)
2014 12% (87) 8% (657)
2015 24% (128) 15% (907)

From this cursory glance at the data it looks like we were in fact correct, with a much higher percentage of adults in our catch this autumn. Why this might be is a bit of a mystery and it'll be interesting to see how this compares to other sites in the southwest and beyond.

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