The Scottish crossbill (Loxia scotica) is a small passerine bird in the finch family Fringillidae. It is endemic to the Caledonian Forests of Scotland, and is the only vertebrate unique to the United Kingdom. The Scottish crossbill was confirmed as a unique species in August 2006, on the basis of having a distinctive bird song.
History and current status
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 red crossbill or the parrot crossbill, both of which also occur in the Caledonian Forest.
Research in Scotland has shown that red, parrot and Scottish crossbills are reproductively isolated, and the diagnostic calls and bill dimensions have not been lost. They are therefore good species.
The Scottish crossbill breeds in the native Scots pine (Pinus sylvestris), Caledonian forests of the Scottish Highlands, but (perhaps surprisingly), often also in forestry plantations of exotic conifers, notably Larch (Larix decidua and L. kaempferi) and Lodgepole pine (Pinus contorta).
The crossbills are characterised by the mandibles crossing at their tips, which gives the group its English name. They are specialist feeders on conifer cones, and the unusual bill shape is an adaptation to assist the extraction of the seeds from the cone. The Scottish crossbill appears to be a specialist feeder on the cones of pines (Scots pine and Lodgepole pine) and larch.
Adult males tend to be red or orange in colour, and females green or yellow, but there is much variation.
The Scottish crossbill is extremely difficult to separate from the red and parrot, and plumage distinctions are negligible. The head and bill size is intermediate between and overlapping extensively with the other two, and extreme care is needed to identify this species. The metallic jip call is probably the best indicator, but even this needs to be recorded and analysed on a sonogram to confirm the identity.
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 that, especially given the physical similarities with other crossbills, they only attract and pair with potential mates of the same species.
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.
The calls can be distinguished by sonograms. 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 and help in any conservation programmes for the race.
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The first survey of Scottish crossbills was in 2008.
- BirdLife International (2012). "Loxia scotica". IUCN Red List of Threatened Species. Version 2013.2. International Union for Conservation of Nature. Retrieved 26 November 2013.
- In the past, this claim has been made on behalf of other species such as the red grouse (now considered to be a sub-species of willow ptarmigan) and Irish stoat (Mustela erminea hibernica), also now considered to be a sub-species of stoat. Loxia scotica 's position as a true species is a matter of debate but the current consensus is that it does have this status (see for example Miles and Jackman (1991) pp. 21–30 and Benvie (2004) p. 55.) The position of the freshwater fish the vendace Coregonus vandesius is disputed, with many authorities considering it to be a synonym of Coregonus albula.
- Adams, William Mark (2003) Future Nature. British Association of Nature Conservationists p. 30. Retrieved 14 July 2009. This source lists the UK's endemic species as being "14 lichens, 14 bryophytes, 1 fern, 21 higher plants, 16 invertebrates and 1 vertebrate (the Scottish crossbill)."
- Perhaps because endemic vertebrates are all but absent from the UK neither SNH nor JNCC appear to provide a definitive "list" but it is clear that the Scottish crossbill is the only endemic bird, (Gooders (1994) p. 273. and "Scottish Crossbill: Loxia Scotica (pdf) JNCC. Retrieved 7 July 2009.) and that there are no endemic freshwater fish (Maitland, P. and Lyle A.A. (1996) "Threatened freshwater fishes of Great Britain" in Kirchofer, A. and Hefti, D. (1996) Conservation of Endangered Freshwater Fish in Europe. Basel. Birkhauser.) or mammals ("The British Mammals list" ppne.co.uk. Retrieved 7 July 2009.) in Britain. There are too few amphibians and reptiles native to the UK for there to be any doubt that no endemic species exist. The position is implied, although not stated by SNH in their Information and Advisory Note Number 49 "Priority species in Scotland: animals" Retrieved 7 July 2009. See also Myers, Norman (2003) "Conservation of Biodiversity: How are We Doing?" (pdf) The Environmentalist 23 pp. 9–15. Retrieved 7 July 2009. This publication confirms there is only one "endemic non-ﬁsh vertebrate species" in the British Isles, although it fails to identify the species concerned.
- "Status of 'UK's only endemic bird species' confirmed", RSPB Scotland
- "'Accent' confirms unique species" BBC Scotland, 15 August 2006
- Adams (2003) p. 30
- Jobling, James A. (2010). The Helm Dictionary of Scientific Bird Names. London, United Kingdom: Christopher Helm. pp. 231, 351. ISBN 978-1-4081-2501-4.
- Summers, R. W.; Dawson, R. J.; Phillips, R. E. (2007). "Assortative mating and patterns of inheritance indicate that the three crossbill taxa in Scotland are species". Journal of Avian Biology. 38 (2): 153–162. doi:10.1111/j.0908-8857.2007.03798.x.
- "Climate risk 'to million species"
- Adams, W. M. (2003) Future Nature. Earthscan.
- Benvie, Neil (2004) Scotland's Wildlife. London. Aurum Press. ISBN 1-85410-978-2
- Miles, H. and Jackman, B. (1991) The Great Wood of Caledon. Lanark. Colin Baxter Photography. ISBN 0-948661-26-7
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