Wednesday, 14 August 2013

Two-barred Crossbills

The final weeks of July saw an influx of crossbills arrive in the county, with small parties of birds much in evidence here in the Brecks and also noted elsewhere across Norfolk and Suffolk. That these were newly arrived birds rather than local breeders was apparent from the upturn in the number of individuals seen and heard. It had been a quiet year for the species locally and crossbills had been only an occasional sighting on my local forest patch during the first half of the year.

Arrivals of this kind tend to occur in late summer and reflect a good breeding season to the north (into Norway, Sweden, Finland and Russia) followed by a poor cone crop, which forces the birds to move further afield in search of food. The recent arrivals may well prove to be the early part of a larger influx over the coming weeks, and it is likely that some of these birds will remain to breed next year, topping up the population breeding within Thetford and other blocks of conifer forest.

Perhaps the most exciting aspect of the arrival has been the presence of another species of crossbill within these small parties of birds. The two-barred crossbill is a superficially similar bird but has two broad white wing bars, white edges to the tertial feathers and a somewhat different call. Even so, it requires patience to work through a party of feeding crossbills with a telescope and to pick out this the rarer of the two species. There is the added complication that some common crossbills show similar barring on their wings, although this is less extensive and seen in only one in a thousand individuals.

Fortunately, I managed to catch up with one of the juvenile two-barred crossbills that have been present within the common crossbill flocks feeding in the larches at Lynford Arboretum. A late afternoon stakeout delivered the goods, so to speak, and I was treated to a wonderful 20 minutes of the bird feeding alongside some common crossbills, even managing to secure a ‘record’ shot with a camera pushed up against the scope. It was amazing to think that this bird had been born earlier this year somewhere in the boreal forests of northern Scandinavia.

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