Scottish crossbill confirmed as an endemic species.

25/03/2007 00:00:00 RSPB research has proved that the Scottish crossbill is a separate species, and thus becomes Britains only endemic bird.

The ‘Celtic’ crossbill differs in bill size from other crossbills in Britain, and they have also been found to have a distinct call, which may well be the method used by the birds to ensure that they only mate with other ‘Celtic’ crossbills.

The British Ornithologists Union has classed the Scottish crossbill as a separate species since 1980, but some ornithologists, including those from the RSPB have reserved judgement, in the belief that there was insufficient scientific research for its formal acceptance.

Scotland’s conifer woodlands harbour 3 species of crossbill – the common crossbill (with a small bill), the parrot crossbill (with a large bill) and the Scottish crossbill (with an intermediate bill size). All 3 are of similar size and plumage, and DNA tests showed that the birds are genetically similar, casting doubt on the Scottish crossbill’s status as a distinct species. Research to discover exactly what features the birds used to identify each other was conducted by experts from the RSPB. Apart from the calls of the 3 types of crossbill, Scottish crossbills (as identified by bill size) also have quite different flight and excitement calls from other crossbills. Other important evidence has come from the RSPB’s long-term field study in the Highlands which focused on discovering if the birds mate with those with a similar bill size and call, and whether young Scottish crossbills inherit their bill sizes from their parents.

Although the 3 species differ in average bill size, the actual differences are too small to be used in the field by ornithologists to differ between crossbills. The calls, though, can be distinguished by sonograms, or sound pictures, made up from recordings. Crucially, this provides the basis for a method to survey crossbills and, for the first time, gain a clear picture of their numbers and distribution in Scotland.

The next steps in the Scottish crossbill study are to discover its population size and habitat requirements. With an estimate of 1,500 birds for its total population being little better than a guess, a detailed survey is important to put create the right conservation and management measures to protect and conserve it.

RSPB Scotland’s senior researcher Dr Ron Summers, who led the study, said: ‘The question of whether the Scottish crossbill is a distinct species, and therefore endemic to the UK, has vexed the ornithological world for many years and split the bird watching community.

‘This research proves that the UK is lucky enough to have a unique bird species that occurs here and nowhere else – and this is our only one. This is very significant. Now that we have shown the Scottish crossbill exists and is endemic we must focus our conservation efforts in making sure that it not only survives, but flourishes and that Scotland has plenty of the habitat that supports and maintains the population of these birds, of which we should be justly proud.’

Dr Jeremy Wilson, head of research for RSPB Scotland, said: ‘Clarifying the status of the Scottish crossbill as a distinct species, and devising a survey method based on the bird’s calls are exciting steps forward. We hope to carry out the first full survey of the numbers and distribution of Scottish crossbills in 2008, after which we will be better placed to understand how best to manage conifer woodlands in Scotland to secure the future of a bird found nowhere else in the world.’