Un endemisme ornitològic ignorat: el trencapinyons balear (Loxia balearica)

Abstract

Crossbills (genus Loxia) are one of the least known groups of extratropical birds. Their diversification has been associated with the large changes suffered throughout the Pleistocene by the boreal forests in which they live. In the Balearics there is a sedentary population in Mallorca, and their occasional presence on the other islands seems due to the arrival of birds sporadically irrupting into western Europe and the Mediterranean. Resident crossbills are distinguished by their small body size; shorter, thicker, and more arched bill, with a shorter lower mandible; comparatively shorter wings; and paler, greyer plumage. They have maintained their identity since the upper Pleistocene at least, indicating reproductive isolation from their continental congener, from which they exhibit fixed genetic differences. Their divergent morphology can be interpreted as an adaptation to the exploitation of pine woods with an irregular food yield in insular conditions. The evidence from morphometrics, palaeontology, molecular genetics, ecology and biogeography indicates that this is an endemic species: Loxia balearica (Homeyer, 1862). The Balearic crossbill is a species deserving closer study, and perhaps priority conservation measures. Its recognition as a distinct species, together with what has been done for the Balearic shearwater, implies that the Balearics are an endemic bird area of global importance, unique in western Europe.