Morphometric characterisation of treecreepers (genus Certhia )
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ORIGINAL ARTICLE
Morphometric characterisation of treecreepers (genus Certhia) Dieter Thomas Tietze Æ Jochen Martens
Received: 8 October 2007 / Revised: 4 November 2008 / Accepted: 5 November 2008 / Published online: 11 December 2008 Ó Dt. Ornithologen-Gesellschaft e.V. 2008
Abstract Lengths of hind claw, tarsus, bill, wing and tail plus bill depth and width, wing tip and tail graduation were measured in nearly 2,000 specimens from all nine currently accepted Certhia species and most subspecies to provide morphometric characterisation. In a discriminant analysis for all species, only C. [discolor], C. nipalensis and C. tianquanensis were clearly separated from each other and from the remaining set of five species. Nevertheless, a cluster analysis produced dendrograms approximating the current molecular phylogeny of the genus. Thus, there is an overall relatively low morphometric diversity among Certhia treecreepers. Recently split allospecies can only partly be distinguished: the disjunct C. [discolor] taxa exhibit no clear affiliation to either allospecies, C. discolor or C. manipurensis, while in C. [familiaris] the species split is corroborated on one hand by a break in geographic trends and on the other by clear separability of neighbouring heterospecific populations. Also, in areas of sympatry, Certhia species differ markedly in body measurements related to the peculiar adaptations of treecreepers to their habitat (tree bark): i.e. bill, claw and tail measurements. The same applies to sexual dimorphism: males, on average Results of the Himalaya Expeditions of J. Martens, No. 264. – For No. 260 see: Vertebrate Zoology 58(2):233–265, 2008. Communicated by F. Bairlein. D. T. Tietze (&) J. Martens Institut fu¨r Zoologie, Johannes Gutenberg-Universita¨t, 55099 Mainz, Germany e-mail: [email protected] D. T. Tietze Museum fu¨r Tierkunde, Staatliche Naturhistorische Sammlungen, Ko¨nigsbru¨cker Landstraße 159, 01109 Dresden, Germany
larger in all body measurements, have, in particular, longer bills, possibly in order to better exploit the limited food and partition it between the two sexes. Keywords Certhia Morphometrics Niche partitioning Sexual dimorphism
Introduction The genus Certhia (treecreepers) unites small passerine birds of uniform outer appearance. The combination of long, curved pincer-like bills and stiff woodpecker-like tail feathers makes treecreepers unique and unmistakable among all Holarctic small passerines. Climbing with tail support is accompanied by derived modifications of the hind-limb musculature (Moreno 1991). Since few species have distinctive morphological characters, the relationships within the genus have been difficult to ascertain, despite the small number of species concerned. Treecreepers are restricted to the Holarctic with local extensions to the tropics. In the larger parts of the genus’ range, there is only one species present, but in Europe two species occur together. In the Himalayas up to four species can be found sympatrically, but a tendency towards vertica
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