. The Canadian field-naturalist. Natural history. 552 The Canadian Field-Naturalist Vol. 115 o o U O o t/) U. 1 Jul 15 Jul lAug 15 Aug 1 Sep 15 Sep Figure 1. Five-day running average of principal component (PC) scores derived from 8 skeletal mensurations and body length of Yellow-headed Blackbirds collected in cen- tral North Dakota during 1987 and 1988. For any 5-day period, mean sample sizes were 63 (range 7-172) for females and 55 (range 7-161) for males. scenarios conformed w^ith our hypothesis of an increase in the proportion of migrants over time. Several possible explanations could acco
. The Canadian field-naturalist. Natural history. 552 The Canadian Field-Naturalist Vol. 115 o o U O o t/) U. 1 Jul 15 Jul lAug 15 Aug 1 Sep 15 Sep Figure 1. Five-day running average of principal component (PC) scores derived from 8 skeletal mensurations and body length of Yellow-headed Blackbirds collected in cen- tral North Dakota during 1987 and 1988. For any 5-day period, mean sample sizes were 63 (range 7-172) for females and 55 (range 7-161) for males. scenarios conformed w^ith our hypothesis of an increase in the proportion of migrants over time. Several possible explanations could account for our inability to detect late-summer migrants passing through central North Dakota. Most likely, our prin- cipal component and discriminant function models had insufficient power to discriminate along the morphometric cline exhibited by Yellow-headed Blackbirds. Our ability to detect migrants may have also been hindered by a failure of migrants to dis- place locally breeding birds but instead congregating in heterogeneous populations within central North Dakota throughout late summer. Alternatively, despite data from returns of banded birds that indicate a southeasterly migration route is used by Yellow-headed Blackbirds, it is possible that most migrants passing through our central North Dakota study area may have originated in more proximate locations in southern Manitoba and eastern Saskatchewan. Populations within these rel- atively nearby breeding locations share greater mor- phometric similarity with birds breeding in central. Please note that these images are extracted from scanned page images that may have been digitally enhanced for readability - coloration and appearance of these illustrations may not perfectly resemble the original Ottawa Field-Naturalists' Club. Ottawa, Ottawa Field-Naturalists' Club
Size: 1299px × 1924px
Photo credit: © Book Worm / Alamy / Afripics
License: Licensed
Model Released: No
Keywords: ., bookcentury1900, bookdecade1910, booksubjectnaturalhistory, booky
