This small kingfisher has a relatively large bill and a conspicuous white collar. Both sexes are green, the male distinguished by a rufous breast. The species is somewhat larger than the American Pygmy Kingfisher (Chloroceryle aenea), but only about two-thirds the size of the Belted Kingfisher (Ceryle alcyon) and half the size of the Ringed Kingfisher (C. torquata).
Green Kingfishers eat mostly small fish, making shallow dives from perches over open water to capture prey in their bills. Pairs nest mainly in the banks of streams, digging burrows with entrances usually covered with vegetation. In Texas and Arizona, the species seems to need clear-water habitats. Unlike larger kingfishers, this one is able to make use of extremely small streams to find suitable nesting and foraging sites.
The Green Kingfisher is widely distributed from the southern United States, where it is found only in south Texas and Arizona, south through Middle America and South America, as far south as central Argentina. Never abundant in the United States, the species suffered a decline in and around major cities in Texas after World War II because of urban development—loss of waterways through damming and irrigation; some previously freshwater systems became muddied, and Green Kingfishers avoided them. Recent conservation efforts have yielded small increases in the U.S. population of the species.
There are few studies of this species despite its extensive range. Remsen (Remsen 1991a) studied the community ecology of Green Kingfishers in association with other kingfisher species in Colombia and Bolivia, and Willard (Willard 1985) analyzed the foraging ecology of the species in Peru. A. Skutch ([in Bent 1940a], Skutch 1977, Skutch 1983a) has described several aspects of its breeding biology and plumages in Central America. Research on the species in North America is missing.