Great Blue Herons, Ardea herodias, are the largest herons of North America. They mainly eat fish and have been known to choke to death on prey that is too large. Males and females are similar in appearance with males being slightly larger than females. They both have white faces and crowns with a pair of black plumes running from above the eye to the back of the head. More plumes grow on the lower back during the breeding season. Immature herons have darker crowns, lack plumes and the shaggy neck feathers like adults. Bills are mainly yellow becoming orange during breeding. They have red-brown thighs with lower yellow-grey legs becoming orange during breeding. They mature at 22 months and typically breed from March to May. They are monogamous during the breeding season usually choosing a new mate each year. They breed in colonies mainly in trees close to wetlands. A group of herons is known as a battery, hedge, pose, rookery, and scattering. Nests are often reused and both parents feed their young.