CROSSBILLS

By Garth Lowe

To birdwatchers in Britain, this is always an interesting bird to find and observe. Crossbills are elusive and unpredictable, but are often at ease when they are feeding, on their exclusive diet of pine seed. The endemic Scottish crossbill is confined to N Scotland, but the common crossbill may be found throughout Britain and N Ireland. Their dependence on conifers for pine seed means that in some years they may have to move large distances to stay alive. Pines only produce seed as they mature, and some of these crops vary annually. Often only short distances are travelled, but occasionally Britain sees large numbers arrive in the late autumn. They erupt from Europe, sometimes in large numbers, and may be spread over many parts of Britain.

The autumn of 2002 saw such an increase, with parties being seen in many of our pine forests in Worcestershire and Herefordshire. Usual spots were the Wyre Forest, with other sightings from Queens Wood, near Dymock, the High Vinnals and Wigmore Rolls near Ludlow, and also Wapley Hill, beyond Leominster.

Larch seed is also taken when available, which is how I came to be at Ravenshill Nature Reserve, one morning in early October, following a grateful call from another member of Wychavon Ringing Group. They had been noticed there, feeding in larches, so an attempt was made to try and catch them for ringing as part of normal activity, carried out under the British Trust for Ornithology's ringing scheme.
Their diet of pine seed has one feature that the birds cannot avoid. They get quite thirsty! On this food supply, they are forced to come down regularly to drink. The pools at this reserve were an obvious choice, and to encourage them down to one spot, a recording of their song and chirrups was played.
This was successful, and six birds were eventually caught in a mist net, set up along the pool margin.

Male crossbill caught under licence for ringing at Ravenshill Photo R M Bishop

The big surprise was that the first bird taken out of the net already carried a ring! It proved to be a bird from Norway - a first year bird, which may have been ringed as a nestling early in the year. Details of its capture will eventually find its way back to us once this control, as it is called, is sent in to the BTO.
An interesting comparison, is the fact that here was one bird out of six, already having a ring on, whereas in the winter of 2001/2002, when a large catch of fieldfares was made, not far away in Suckley, and only one was found to be ringed, out of a total of 1771 birds (Brown 2002).

The ages and sex of this small group was also interesting. One of them was a male, aged as an adult, born in 2000, or earlier, the other male was a this year's (2002) bird. Of the other four, all were sexed as females, two born this year and two the year before.

This irruption from Europe raises some interesting questions, one being - how do these birds know that Britain is away to the south west, and has an alternative supply of food? Do any of them miss us, and when do they give up flying further into the Atlantic Ocean? Other migrating species, that also winter here, have been proven to have on occasions overshot us, again by the fact that they were ringed, and their country of origin discovered. Bird migration continues to be a fascinating subject!

Reference
BROWN, S. 2002. Fieldfare orchard. Worcestershire Record No 12 April 2002.