Okay, guys and gals in Orkney and Shetland, what call types are you getting this year ? It would be very interesting to know. Colleagues in Grampian Ringing Group had a ringing recovery of a Common Crossbill in April near Dufftown. This bird was ringed in September 2009 in lower Deeside so had moved Northwards somewhat in the six months since ringing. Was this a bird returning 'back' to where it had come from ? My instinct is 'no', it was possibly part of a nomadic post breeding flock that was seeking a decent cone crop. But the possibility remains, especially given the accepted view is that birds move south and westwards.
So if this years influx of Commons on the Northern Isles is giving 4E calls does this mean they are last year's birds going home ? Maybe and maybe not. Maybe, for the scant evidence cited above and 'not' because some 4E's may have remained in Fennoscandia where there was a localised food source and are only moving now after breeding ( there are juvs in the recent photos I have seen of birds on Shetland). This is this 'lag' effect I spoke of last year, and this would depend on how far from the East the birds were erupting. However, if the calls of this years irruption is different from 4E then at least it rules out the 2009 population returning or a new one of the same type irrupting. As I recall there were some 1A's and 1B's last year also, though in much smaller numbers than the 4E's.
4E Common Crossbill
The other intruiging possibility is that of small numbers of Crossbills trickling in during the winter months and early spring. I have had Common Crossbills at coastal sites in November and December and two flew over my garden this April ( there is no substancial viable food source near me and I am less than a mile from the coast). These may also have been birds moving Northward back up the coast. However, I would expect the legions of Vismiggers to have picked up such movements if they were happening with any regularity ?
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