Geographic variation in the house sparrow (Passer domesticus) in New Zealand

Abstract

Geographic variation in size and colour is studied in five populations of the house sparrow, Passer domesticus (Linnaeus), in New Zealand. Geographic variation in size does not, in general, follow a clinal pattern and is not consistent for all size characters studied. However, there is some evidence for a trend towards larger size in some characters in the Hastings and Christchurch populations. The smallest birds were found in Southland, which is the most southerly of the populations studied. Correlations with climatic variables do not give consistent evidence of conformity with Bergmann's and Allen's ecogeographic rules. In fact, the wing length in both sexes shows positive regression on mean daily maximum temperatures for January, the hottest month in the New Zealand summer. Some age variation and sexual dimorphism in size characters is displayed by the specimens examined. Males are larger than females, and adults than juveniles, for most characters studied. Geographic variation in belly colour in females shows a significant correlation with mean annual rainfall, but the correlation in males is weaker. The distribution of minor plumage variants is studied. These variants include the occurrence of chestnut on the black bib and on the rump of males, "Hispaniolensis"-type streaking on the breast of males, and belly-streaking in males and females. Since the inception of this study, Johnston and Selander (1971), using principal component analyses, have demonstrated in 16 skeletal characters of North American house sparrows the existence of covariant sets which bear different relationships to environmental factors.