Blackbirds prefer to roost in wooded areas and marshes near farmlands. The birds nest apart from each other to raise their young in the spring and early summer, and congregate into flocks of thousands or even millions in the late summer and fall. With a seed-based diet, large flocks of birds tend to descend upon fields, lawns, and farms to eat cereal grains, corn, rice, nuts, and fruit. Although blackbirds also eat insects and bugs, their destructive feeding on farm crops is what makes them potentially dangerous nuisances.