The Micronesian Kingfisher is a species of kingfisher from the Pacific Islands of Guam Pompeian and Palau. One of its subspecies the Guam Kingfisher is restricted to a captive breeding program following its extinction in the wild due to the introduced brown tree snake.In addition, the mysterious extinct Ryukyu Kingfisher, known from a single specimen, is sometimes placed with the Micronesian taxon as a subspecies . Among island differences in morphological behavioral and ecological characteristics have caused some to suggest that Micronesian Kingfisher populations should be split into separate species.The subspecies are distinguished primarily by variations in plumage and size, with the Palau birds being smallest and Guam kingfishers being largest . This is a brilliantly colored, medium sized kingfisher, 20-24 cm in length. They have iridescent blue backs and rusty-cinnamon heads. Adults on Pompeian and Palau are characterized by white underparts, while juveniles are cinnamon below. To the contrary, the adult male Micronesian Kingfishers from Guam have cinnamon underparts and Guam females and juveniles are white below. All subspecies have large laterally-flattened bills and dark legs. The calls of Micronesian Kingfishers are generally raspy chattering and they differ in cadence and pitch among islands.