I was having a think about the likely origin of the Barnes Bitterns. I assume that the birds we get at the start of the season are from Scandinavia or Baltic states whereas when we get individuals later in the year these are either displaced by hard weather from elsewhere in the UK or from the continent. I did find some interesting info on just how widespread Bitterns are in winter compared with the highly localised breeding population.
Below: winter distribution of Bitterns.
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| Sites where Bitterns were recorded between October 2009 and March 2010 (Source: RSPB) |
This compares with the breeding distribution of confirmed booming males (left, blue dots) and confirmed nesting attempts (right, purple dots).
Source: RSPB.
The 2009-10 winter was pretty hard so this may exaggerate the difference - with more sites reporting Bittern than usual.
More info on this
article from Birdguides.
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