Brown-headed cowbirds are polygamous, promiscuous birds that do not build nests or tend their own young. Instead, they are brood parasites – the female bird will lay a single oval, light blue egg with brown flecks in another species' nest and leave it for the host birds to incubate and raise the hatchling. One female may lay 10-36 eggs in other nests, and more than 220 different species of birds have been documented as brown-headed cowbird hosts.
I took these pictures along the Hackensack River on the Hackensack side of FDU.