Vocal types in crossbill populations (Loxia spp.) of Southwest Europe

Abstract

The evolution of crossbills is one of the most fascinating topics in evolutionary ecology. Recent studies have shown an astonishing divergence in terms of vocalisation between morphologically quite similar crossbill populations in the Red/Common Crossbill complex (Loxia curvirostra) of North America and Europe. Some evidence even indicates the existence of ''cryptic'' species with different vocal types and bill sizes, which are adapted to different conifer species. However, there is so far no strong genetic evidence for the existence of separate species, although assortative mating occurs with respect to bill size. To understand the role of vocalisation in the speciation process of crossbill taxa, basic studies that assess the distribution of vocal types of crossbills and the use of different habitats and resources are needed. In our study, we investigated the occurrence of crossbill vocal types in Southwest Europe. In addition to the well-known vocal types described first by Robb (Dutch Birding 22:61-107, 2000) for the Benelux and Great Britain, we discovered at least six more vocal types in the Mediterranean area. Some vocal types were found exclusively in rather small areas, e.g. in the Pyrenees, the Sierra de Cazorla, Sierra de Javalambre and on Corsica, and appeared to be tightly linked to certain habitat types and pine species. Overall, vocal types in the Mediterranean had a more local occurrence than vocal types from northern populations, which were more widely distributed. This might reflect the nomadic behaviour of northern European crossbills, which feed, in contrast to Mediterranean crossbills, mostly on rather unstable food sources, especially spruce seeds. Furthermore, the vocal types of Mediterranean crossbills show at least some similarities to the vocal types of the rather sedentary crossbills of North Europe (L. pytyopsittacus, L. scotica), which are as well adapted to pine seeds. This might reflect a common ancestry of crossbills adapted for pines. We therefore suggest the existence of two main groups of crossbills in Europe: one group that is rather sedentary and feeds mainly on pine seeds (L. pytyopsittacus, L. scotica and the Mediterranean forms), and another group in Central, Northern and Eastern Europe that is highly nomadic and mostly feeds on spruce seeds (L. curvirostra). Further studies are needed to unravel the consistency of vocal types and the genetic relationship between the different forms, and to provide more evidence for the degree of assortative mating of crossbills with distinct vocalisation breeding in sympatry.

Classification of behavior using vocalizations of Pacific white-sided dolphins (Lagenorhynchus obliquidens)

“…The strong behavioral and vocal distinctions between the two groups may in fact demonstrate that these groups are in the process of speciation, if not fully genetically distinct. Vocal differences have been used to distinguish cryptic species that are genetically different but morphologically similar (Smith and Friesen, 2007;Braune et al, 2008;Foerschler and Kalko, 2009) and may develop as a precursor to genotypic divergence. To fully verify this hypothesis, concurrent acoustic and genetic sampling needs to be conducted on these animals to determine if the click types represent the genetically distinct populations that have already been shown to overlap in the SCB (Lux et al, 1997).…”

The genetic structure of crossbills suggests rapid diversification with little niche conservatism

“…Under the second scenario it is thought that the spruce-feeding common crossbill invaded Europe west of the Ural Mountains after the last glaciation (with the spread of Norway spruce) and that upon reaching Mediterranean areas it shifted resource type and started to utilize the different pines. Both hypotheses have some empirical support: Mediterranean pine-feeding crossbills are vocally more similar to the other pine-feeding crossbills from the north (Summers & Jardine, 2005;Förschler & Kalko, 2009), but morphologically more similar to the northern spruce-feeding common crossbill (Cramp & Perrins, 1994) which moreover regularly irrupts to Mediterranean areas (Tellería, Asensio & Díaz, 1999;Borrás et al, 2010) and probably has done so in the past.…”

Coevolution between crossbills and black pine: the importance of competitors, forest area and resource stability

“…, 2007; Edelaar et al. , 2008; Förschler & Kalko, 2008). However, the extent to which specialization on individual conifers and ensuing coevolution has contributed to this diversity is little known (but see Mezquida & Benkman, 2005).…”

“…, 2008) and we therefore recognize the Cyprus crossbill as a distinct taxon. The Corsican crossbill has also been recognized, however, it is uncertain whether these birds are morphologically or vocally distinct from common crossbills on the mainland (Griscom, 1937; Massa, 1987; Clouet & Joachim, 1996; Robb, 2000; but see Förschler & Kalko, 2008). Indeed, Robb (2000) suggests that vocal ‘type B’ crossbills are adapted for foraging on the cones of black pine and occur throughout much of the range of black pine including Corsica but not Cyprus.…”

“…In Eurasia, as in North America, common (red) crossbills (L. curvirostra L.) are comprised of a group of morphologically and vocally diverse forms (Newton, 1972;Cramp & Perrins, 1994;Clouet & Joachim, 1996;Robb, 2000;Summers & Jardine, 2005;Summers et al, 2007;Edelaar et al, 2008;Fö rschler & Kalko, 2008). However, the extent to which specialization on individual conifers and ensuing coevolution has contributed to this diversity is little known (but see Mezquida & Benkman, 2005).…”