Geographical and Sexual Variation in the Long-Tailed Jaeger Stercorarius Longicaudus Vieillot

Abstract

Manning, T. H. 1964. Geographical and sexual variation in the Long-tailed Jaeger, Stercorarius longicaudus Vieillot. Biol. Pap. Univ. Alaska, No. 7. Pp. iii + 16 (Author's address: RR 1, Merrickville, Ontario, Canada) Statistical comparison of the color of the underparts of 474 Nearctic and 64 western and central Palearctic sexed specimens of Long-tailed Jaegers indicates that S. l. pallescens Loppenthin is a valid race ranging across the Nearctic and eastern Siberia to the Indigirka River. Spitsbergen specimens are also referable to this race; Iceland specimens belong to S. l. longicaudus. Females are significantly darker than males. The origin and migration of the two races are discussed. bills and wings of Nearctic males are shorter than those of females, and there are significant geographical differences within the Nearctic population. Regression and correlation statistics for wing and bill lengths are given and discussed. Thirty-two weighed specimens indicate that within populations weight is correlated with wing length but not with bill length.