Abstract

Crossbills of different size in Scotland give different flight and/or excitement calls. Generally, crossbills that give a particular flight call also give a particular excitement call, thereby defining ‘call-types’. Here, different calls and their varieties are described for different sizes of crossbill (i.e. species). Also described are the different call-types of Common Crossbills Loxia curvirostra of varying average size (wing length and bill size). Using calls to identify crossbills is less subjective than trying to discern small differences in bill size, and the results of this study may help observers who record crossbill calls.Three species of crossbill breed in Britain: Common Crossbill Loxia curvirostra, Scottish Crossbill L. scotica and Parrot Crossbill L. pytyopsittacus (Gibbons et al. 1993; Balmer et al. 2013). This is the accepted taxonomy of the British Ornithologists’ Union (following the IOC World Bird List; Gill & Donsker 2019) and of BirdLife International (HBW & BLI 2019). Our current understanding of Britain’s breeding crossbills is that the Scottish Crossbill is a resident endemic while Common and Parrot Crossbills result from irruptions (irregular movements of large numbers of birds into areas where they are not normally found) from continental Europe and western Asia (Nethersole-Thompson 1975; Cramp & Perrins 1994; Newton 2006). Irrupting birds may stay to breed in Britain, but thereafter may return to the continent in subsequent years (Newton 1972, 2006). It is also possible that some Common and Parrot Crossbills are longer-term residents, although they may move about within Britain from year to year. The three species are not easy to distinguish in the field on the basis of morphological features because of their similarity in plumage and overlap in biometrics (Knox 1976, 1990). Measurements of Scottish Crossbills overlap partially with both Parrot Crossbills (the largest of the three species) and Common Crossbills (the smallest; Knox 1976).