Scottish crossbill

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 terrestrial vertebrate species endemic to the United Kingdom.[2][3][4] The Scottish crossbill was confirmed as a unique species in August 2006, on the basis of having a distinctive bird song.[5][6][7]

Scottish crossbill
Scientific classification Edit this classification
Domain: Eukaryota
Kingdom: Animalia
Phylum: Chordata
Clade: Dinosauria
Class: Aves
Order: Passeriformes
Family: Fringillidae
Subfamily: Carduelinae
Genus: Loxia
Species:
L. scotica
Binomial name
Loxia scotica
Hartert, 1904

The genus name Loxia is from Ancient Greek loxos, 'crosswise', and scotica is Latin for 'Scottish'.[8] The Scottish Gaelic name for a crossbill is Cam-ghob, which means 'crooked beak'.[9]

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.

RSPB research showed that Scottish crossbills have quite distinct flight and excitement calls from other crossbills – some even stated they have "Scottish accents".

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.[10]

The population is thought to be approximately 20000 birds.[11] It nests in pines or other conifers, laying 2-5 eggs.

The Scottish crossbill breeds in the native Scots pine (Pinus sylvestris), Caledonian forests of the Scottish Highlands, but often also in forestry plantations of exotic conifers, notably Larch (Larix decidua and L. kaempferi) and Lodgepole pine (Pinus contorta).

This species of crossbill is resident, and is not known to migrate. It will form flocks outside the breeding season, often mixed with other crossbills.

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.

Bill structure

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.

Calls

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.

Conservation

The first survey of Scottish crossbills was in 2008.[12]

Despite lacking data for population trends, British Birds places the crossbill on their Amber list for conservation concern on the basis of it being an endemic species and therefore of 'international importance'.[13] A 2017 report by the British Trust for Ornithology identified the crossbill as being at high risk of extinction.[14]

Breeding populations exist at Corrimony Nature Reserve,[15] and Loch Garten Nature Reserve, one of the United Kingdom's most protected nature sites.[16]

One of the main threats to the crossbill's habitat is wood and pulp plantations, plus underplanting conifers and grazing pressure.[17]

The main active conservation initiative is the implementation of the EU Biodiversity Action Plan, which seeks to protect the numerous species of birds throughout the EU. Further studies are needed to establish the species of trees crossbill's best adapt to, as well as to establish population trends. It has also been suggested to prevent any further loss of habitat, and further restrict grazing.[17]

Notes
  1. BirdLife International (2016). "Loxia scotica". IUCN Red List of Threatened Species. 2016: e.T22720641A88690876. doi:10.2305/IUCN.UK.2016-3.RLTS.T22720641A88690876.en. Retrieved 12 November 2021.
  2. 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.
  3. 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)."
  4. 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" Archived 2011-07-28 at the Wayback Machine 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" Archived 2016-11-09 at the Wayback Machine Retrieved 7 July 2009. See also Myers, Norman (2003) "Conservation of Biodiversity: How are We Doing?" Archived 2011-07-16 at the Wayback Machine (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.
  5. "Status of 'UK's only endemic bird species' confirmed", RSPB Scotland
  6. "'Accent' confirms unique species" BBC Scotland, 15 August 2006
  7. Adams (2003) p. 30
  8. 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.
  9. "Forestry and Land Scotland - Scottish Crossbill". forestryandland.gov.scot. Retrieved 2019-04-25.
  10. 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.
  11. "Scottish Crossbill (Loxia scotica) - BirdLife species factsheet". Archived from the original on 2014-11-07. Retrieved 2014-11-06.
  12. SUMMERS, R., & BUCKLAND, S. (2011). A first survey of the global population size and distribution of the Scottish Crossbill Loxia scotica. Bird Conservation International, 21(2), 186-198. doi:10.1017/S0959270909990323
  13. Eaton, Mark (December 2015). "Birds of Conservation Concern 4: the population status of birds in the UK, Channel Islands and Isle of Man" (PDF). British Birds. 108: 708–746.
  14. Hayhow, DB et al. "The state of the UK’s birds 2017" (PDF) Sandy, Bedfordshire: The RSPB, BTO, WWT, DAERA, JNCC, NE and NRW.
  15. "Corrimony Nature Reserve, Highland, Scotland". The RSPB. Retrieved 2020-11-24.
  16. "Loch Garten Nature Reserve, Abernethy, Scotland". The RSPB. Retrieved 2020-11-24.
  17. BirdLife International (1 October 2016). "Loxia scotica, Scottish Crossbill". The IUCN Red List of Threatened Species. doi:10.2305/IUCN.UK.2016-3.RLTS.T22720641A88690876.en. ISSN 2307-8235. Retrieved 31 July 2023.

References
  • 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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