Summers, R. W.; Dawson, R. J.; Phillips, R. E. Assortative mating and patterns of inheritance indicate that the three crossbill taxa in Scotland are species. Journal of Avian Biology. 2007, 38 (2): 153–162. doi:10.1111/j.0908-8857.2007.03798.x.引文使用过时参数coauthors (帮助)
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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)