Abstract

I analyzed variation in 24 measurements on the skeletons of 2281 breeding Savannah Sparrows (fasserculus sandwichensis) from 65 different localities to describe patterns of geographic variation in size and shape.The samples come from virtually throughout the species' breeding range, from northern Canada and Alaska, south to the northeastern United States, central Great Plains, and in the highlands of the west, south to central Mexico.For the most part, the interpopulational variation in size is clinal, with considerable overlap among geographically contiguous populations.The most striking finding of this study is that Savannah Sparrows are large on islands, as would be predicted by some theory.The largest Savannah Sparrows are from Sable Island, Nova Scotia, and the Aleutian Islands, Alaska.Although both are islands, these two areas are ecologically different in many ways.On Sable Island, the Savannah Sparrow is the only breeding passerine, whereas on the Aleutians, Lapland Longspurs (Calcarius lapponicus) as well as Savannah Sparrows are abundant, and seemingly found in the same habitat; Song Sparrows (Melospiza melodia) and Gray-crowned Rosy-Finches (Leucosticte tephrocotis) also breed there, but generally in different habitats.Thus, one site is sparrow poor, and the other relatively sparrow rich.Savannah Sparrows are also relatively large on the Magdalen Islands, Quebec, and on Middleton Island, Alaska.On the Magdalen Islands, Nelson' s Sharp-tailed Sparrows STUDIES IN AVIAN BIOLOGY NO. 23 there is clinal variation down the Alaskan Peninsula; it is my opinion, therefore, that these should not be recognized as subspecifically distinct because there is no benefit to more or less arbitrarily delimiting taxa that overlap on a phenetic continuum.Viewed in this way my analyses support the recognition of only one subspecies of Savannah Sparrow from North America, P. s. sandwichensis, other than P. s. pn' nceps and the birds resident in west coastal saltmarshes.The nine subspecies of saltmarsh Savannah Sparrows all seem to be clearly separable, and my analyses support the retention of these as valid and distinct taxa.Key Words: Bergmann' s Rule, geographic variation, islands, morphology, Passerculus sandwichensis, Savannah Sparrow, subspecies.there is clinal variation down the Alaskan Peninsula; it is my opinion, therefore, that these should not be recognized as subspecifically distinct because there is no benefit to more or less arbitrarily delim iting taxa that overlap on a phenetic continuum.Viewed in this way my analyses support the recog of only one subspecies of Savannah Sparrow from North America, P. s. sandwichensis, other P. s. princeps and the birds resident in west coastal saltmarshes.The nine subspecies of saltmarsh Savannah Sparrows all seem to be clearly separable, and my analyses support the retention of these as valid and distinct taxa.

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