They forage on wet ground or in shallow water, mainly eating insects, small fish and some seeds. Their most common mode of foraging is to vigorously flip leaves and rip at submerged aquatic vegetation. The mast of small-acorn producing oaks, such as willow oak, is also important. In some areas, the nuts of planted pecans are heavily used. They very rarely will attack small passerine birds, and have been known to kill species as large as the common snipe. They feed in flocks during migration and on the wintering grounds, sometimes joining other blackbirds, both often occurring in single species flocks. They more often roost with other blackbirds; some small roosts are in brushy vegetation in old fields and others are in massive mixed flocks—sometimes in the urban areas.
This page contains full information about Rusty Blackbird Flock.