GEOGRAPHIC-VARIATION IN YELLOW-HEADED BLACKBIRDS FROM THE NORTHERN GREAT-PLAINS

We assessed geographic variability in morphology among Yellow-headed B lackbirds (Xanthocephalus xanthocephalus) collected from breeding popu lations in Minnesota, North Dakota, and South Dakota in the United Sta tes and Alberta, Manitoba, and Saskatchewan in Canada during spring. B oth male and female Yellow-headed Blackbirds tended to be larger in th e more northern breeding populations. Males collected in Manitoba and southeast Saskatchewan tended to be more like populations from the Uni ted States, whereas other populations in Saskatchewan and Alberta popu lations were morphologically similar to each other. For females, howev er, only the Manitoba population was similar to the U.S. populations, and the females from the southeastern Saskatchewan were similar to oth er Saskatchewan birds. Southeastern Saskatchewan appears to represent a transitional region between northwestern and southeastern breeding p opulations of Yellow-headed Blackbirds.