Territory size generally varies with habitat quality, including vegetation structure, food abundance and available space. Bobolink (Dolichonyx oryzivorus), a semi-colonial species, is known to respond to these habitat quality factors individually, though no previous study has examined these factors simultaneously in relation to territory size. We examined the relationship between bobolink territory size and vegetation structure, prey abundance and patch size in hayfields of southern Ontario, Canada. All three factors were influential in explaining variation in territory size. Important prey items were more abundant in small territories. These small territories also had taller and denser vegetation, deeper litter, and less bare soil. Territory size was related to patch size, with smaller territories on smaller fields. We compared our results with other studies that have found links between territory size and individual variables, including factors not in our models.