Reversed sexual size dimorphism, in which females are larger, is usual among hawks and falcons, but sparrowhawks take it further than most. Males typically weigh around 110 to 200 grams and females around 185 to 350 grams.
The difference shows in the food. Males concentrate on small songbirds such as tits, finches and sparrows, while females can take thrushes, starlings and birds up to pigeon size. Since a breeding pair provisions one nest, that division widens the prey base without the two competing directly for the same targets.
Why the dimorphism evolved is still argued. Proposals include prey-size partitioning, female defence of the nest, and constraints imposed by the male's need for agility during courtship feeding. The sparrowhawk is also a well-documented case of pesticide recovery: British populations crashed with organochlorine use in the 1950s and 1960s and rebuilt after restrictions, with the story traced closely through egg-shell thickness records.