The Cooper's hawk is a solitary bird apart from breeding and rare aggregations during migration. This species usually is considered monogamous. However, pairings of two males (1 young, 1 adult) with a single female have been recorded at least three times. In Grand Forks, North Dakota, a single male has been recorded to successfully mate with two nearby females, with similar records from New Mexico. However, the breeding efforts in Grand Forks were found to be disproportionately producing males, seven to one. A Wisconsin study determined 19.3% of nestlings in a Milwaukee study area were from extra-pair couplings and that 34% of all broods included at least 1 extra-pair young. Despite their generally monogamous breeding system, Cooper's hawks are often rather inconsistent regarding breeding for life (as many other birds of prey do). While males are more or less devoted to same breeding sites throughout lifetime, 23% of adult females in Wisconsin moved to differ nesting grounds from away, averaging , in subsequent years. Meanwhile, in Arizona, 3% of males and 10% of females displayed yearly breeding dispersal. However, in the urbanized areas of Tucson, evidence indicates that mate fidelity is higher than elsewhere. In Tucson, it was found that the mean distance of the mated pairs was only during the non-breeding season and 36 interactions were recorded almost all in the core range, indicating an unusually close perennial typical pair bond here. The rate of dispersal to a different breeding ground was a much higher at 68% in north Florida.