Geographic and temporal variation in the diet of Yellow-headed Blackbirds

Yellow-headed Blackbirds (Xanthocephalus xanthocephalus) are presumed predators of sunflower (Helianthus annuus) in the northern Great Plains. Their esophageal contents varied temporally and among three provinces and three states in relation to regional agricultural bases but males contained more sunflower and small grains than females whereas females contained more weed seeds and insects than males. The diets of both sexes frequently included insects but insects comprised only a small proportion of the total dry weight of esophageal contents. In north-central North Dakota, sunflower represented about 50% of the esophageal contents of males in spring and fall but comprised less than 20% of the female diet. Small grains comprised about 25% of the female diet in all seasons and about 40% of summer diet of males. Insects represented about 50% of the diet of females until mid-summer when insects were largely replaced by weed seeds.