Assortative mating also indicates that common crossbill Loxia curvirostra vocal types are species

Abstract

Compared to most other birds, the taxonomy of crossbills (Loxia) is still highly unsettled. However, much progress seems to be achievable when data on vocalisations is included. In a recent paper, Summers et al. (2007) argued that strong assortative mating indicated that parrot crossbill Loxia pytyopsittacus, Scottish crossbill Loxia scotica and common crossbill Loxia curvirostra behave as good species when breeding in sympatry. Here I argue that their data, when placed in the context of other studies, also indicate that three vocally differentiated European populations within the common crossbill are species (following the biological species concept of Mayr (1963): species are groups of interbreeding natural populations that are reproductively isolated from other such groups). If this tentative conclusion remains to be upheld, it might have large repercussions for our understanding of the speciation process as well as for a number of more applied issues such as the discovery and description of biodiversity and the conversation of mobile, cryptic species.