Body size changes in passerine birds introduced to New Zealand from the UK

Abstract

One feature of global geographic variation in avian body sizes is that they are larger on isolated islands than on continental regions. this study aims to assess whether there have been changes in body size following successful establishment for seven passerine bird species (blackbird Turdus merula, song thrush T. philomelos, house sparrow Passer domesticus, chaanch Fringilla coelebs, greennnch Chloris chloris, golddnch Carduelis carduelis, yellowhammer Emberiza citrinella) introduced from the continental islands of the UK to the more isolated oceanic landmass of New Zealand in the middle of the nineteenth century. Measures of tarsus length were taken from individuals from contemporary UK and New Zealand popula-tions of these species, and from historical specimens collected around the time that individuals were trans-located from the UK to New Zealand. Analysis of Variance was used to test for size diierences between contemporary UK and New Zealand populations, and between historical UK and contemporary UK and New Zealand populations. Historical UK populations have longer tarsi, on average, than 12 (7 UK and 5 New Zealand) of the 14 contemporary populations. Signiicant decreases in tarsus length relative to the historical populations have occurred in the UK for blackbird, chaanch and greennnch, and in the New Zealand blackbird population. Contemporary New Zealand house sparrows have signiicantly longer tar-si, on average, than both historical and contemporary UK populations. Exposure to novel environments may be expected to lead to changes in the morphology and other traits of exotic species, but changes have also occurred in the native range. In fact, contrary to expectations, the most common diierences we found Copyright Tim M. Blackburn et al. This is an open access article distributed under the terms of the Creative Commons Attribution License 3.0 (CC-BY), which permits unrestricted use, distribution, and reproduction in any medium, provided the original author and source are credited.