The trogons and quetzals are birds in the order Trogoniformes which contains only one family, the Trogonidae. The family Trogonidae contains 49 species in seven genera. The fossil record of the trogons dates back 49 million years to the Early Eocene. They might constitute a member of the basal radiation of the order Coraciiformes and order Passeriformes or be closely related to mousebirds and owls. The word trogon is Greek for "nibbling" and refers to the fact that these birds gnaw holes in trees to make their nests. Trogons are residents of tropical forests worldwide. The greatest diversity is in the Neotropics, where four genera, containing 34 species, occur. The genus Apaloderma contains the three African species. The genera Harpactes and Apalharpactes, containing twelve species, are found in southeast Asia. They feed on insects and fruit, and their broad bills and weak legs reflect their diet and arboreal habits. Although their flight is fast, they are reluctant to fly any distance. Trogons are generally not migratory, although some species undertake partial local movements. Trogons have soft, often colourful, feathers with distinctive male and female plumage. They are the only type of animal with a heterodactyl toe arrangement. They nest in holes dug into trees or termite nests, laying 2–4 white or pastel-coloured eggs.
Evolution and taxonomy
The position of the trogons within the class Aves has been a long-standing mystery. A variety of relations have been suggested, including the parrots, cuckoos, toucans, jacamars and puffbirds, rollers, owls and nightjars. More recent morphological and molecular evidence has suggested a relationship with the Coliiformes. The unique arrangement of the toes on the foot (see morphology and flight) has led many to consider the trogons to have no close relatives; this would place them in their own order, possibly with the similarly atypical mousebirds as their closest relatives. The earliest formally described fossil specimen is a cranium from the Fur Formation Lower Eocene in Denmark (54 mya). Other trogoniform fossils have been found in the Messel pit deposits from the mid-Eocene in Germany (49 mya), and in Oligocene and Miocene deposits from Switzerland and France respectively. The oldest New World fossil of a trogon is from the comparatively recent Pleistocene (less than 2.588 mya). The family had been thought to have an Old World origin notwithstanding the current richness of the family, which is more diverse in the Neotropical New World. DNA evidence seemed to support an African origin for the trogons, with the African genus Apaloderma seemingly basal in the family, and the other two lineages, the Asian and American, breaking off 20–36 million years ago. More recent studies show that the DNA evidence gives contradictory results concerning the basal phylogenetic relationships; so it is currently unknown if all extant trogons are descended from an African ancestor, an American ancestor or neither.
The trogons are split into three subfamilies, each reflecting one of these splits. Apalodermatinae is the African subfamily and contains a single genus, Apaloderma. Harpactinae is the Asian subfamily and contains two genera, Harpactes and Apalharpactes. Apalharpactes, consisting of two species in Java and Sumatra, has only recently been accepted as a separate genus from Harpactes. The remaining subfamily, the Neotropical Trogoninae, contains the remaining four genera, Trogon, Priotelus, Pharomachrus and Euptilotis. The two Caribbean species of Priotelus are extremely ancient. The two quetzal genera, Pharomachrus and Euptilotis are possibly derived from the final and most numerous genus of trogons in the Neotropics, Trogon. A 2008 study of the genetics of Trogon suggested the genus originated in Central America and radiated into South America after the formation of the Isthmus of Panama (as part of the Great American Interchange), thus making trogons relatively recent arrivals in South America.
Distribution and habitat The majority of trogons are birds of tropical and subtropical forests. They have a cosmopolitan distribution in the worlds wet tropics, being found in the Americas, Africa and Asia. A few species are distributed into the temperate zone, with one species, the coppery-tailed trogon, reaching the south of the United States, specifically southern Arizona and the surrounding area. The Narina trogon of Africa is slightly exceptional in that it utilises a wider range of habitats than any other trogon, ranging from dense forest to fairly open savannah, and from the Equator to southern South Africa. It is the most widespread and successful of all the trogons. The eared quetzal of Mexico is also able to use more xeric habitats, but preferentially inhabits forests. Most other species are more restricted in their habitat, with several species being restricted to undisturbed primary forest. Within forests they tend to be found in the mid-story, occasionally in the canopy. Some species, particularly the quetzals, are adapted to cooler montane forest. There are a number of insular species; these include a number of species found in the Greater Sundas, one species in the Philippines as well as two species endemic to Cuba and Hispaniola respectively. Outside of South East Asia and the Caribbean, however, trogons are generally absent from islands, especially oceanic ones. Trogons are generally sedentary, with no species known to undertake long migrations. A small number of species are known to make smaller migratory movements, particularly montane species which move to lower altitudes during different seasons. This has been demonstrated using radio tracking in the resplendent quetzal in Costa Rica and evidence has been accumulated for a number of other species. The Narina trogon of Africa is thought to undertake some localised short-distance migrations over parts of its range, for example birds of Zimbabwe's plateau savannah depart after the breeding season. A complete picture of these movements is however lacking. Trogons are difficult to study as their thick tarsi (feet bones) make ringing studies difficult.
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