STILL on the Scotland trip there were two birds on our list as ‘definite species to see’ – we dipped on one unfortunately so will have to wait till our next visit to try again.
The birds were Scottish Crossbill and Crested Tit, both specialists of the highland pine forests and the only place to catch up with them here in the UK is Scotland. Despite much searching the Scottish Crossbill eluded us completely and to be honest with the possibility of ID’ing correctly a Scottish as say Common or Parrot Crossbill its no show saved a lot of reading, photo comparisons, discussion etc. The British Ornithologists Union first classed the Scottish Crossbill as a separate and distinct species in 1980, but some ornithologists believed there was insufficient scientific research for its status. It was considered to be possibly a race of either the Common Crossbill or the Parrot Crossbill, both of which also occur in the Caledonian Forest.
RSPB research showed that Scottish Crossbills have quite distinct flight and excitement calls from other crossbills – some even stated they have “Scottish accents”. According to a lengthy scientific study by the RSPB, ‘Celtic’ crossbills differ in bill size from other crossbill species found in Great Britain, and they have also been found to have a distinct Scottish accent or call, thought to be the method used by the birds to make sure they only attract and pair with potential mates of the same race.
The most important evidence to come from RSPB’s long term study in the Highlands 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. Results showed that of over 40 pairs of different types of crossbills caught, almost all matched closely for bill size and calls, so the different types of crossbills were behaving as distinct species.
We did strike lucky with our next bird, again a conifer specialist - the Crested Tit. In Scotland, the crested tit is confined to Caledonian pine forest remnants and pine plantations in Easter Ross, the Beauly catchment (which includes Glen Affric), Strathspey and the Moray Firth coast. It is missing from some of the ancient pinewood remnants, including those on Deeside and at Rannoch, but the reasons for this are not clear, as suitable habitat exists there.
The poor dispersal ability of the species has been suggested as one possible reason for this - the geographical isolation of the forest fragments has resulted in large gaps of treeless ground which the birds are unable to cross in sufficient numbers. The population in Scotland has increased in recent decades, as a result of the expansion of pine plantations. Following three years of study by the RSPB between 1992-95, it was estimated at 7,000 individuals. However, the density of birds in the native pinewoods was almost 10 times that of the plantations, indicating that the ancient forest provides a much more favourable habitat.