The fossil record of the trogons dates back 49 million years to the Early Eocene.

[2][3] The word trogon is Greek for "nibbling" and refers to the fact that these birds gnaw holes in trees to make their nests.

[4] They feed on insects and fruit, and their broad bills and weak legs reflect their diet and arboreal habits.

[4] A variety of relations have been suggested, including the parrots, cuckoos, toucans, jacamars and puffbirds, rollers, owls and nightjars.

The earliest formally described fossil specimen is a cranium from the Fur Formation Lower Eocene in Denmark (54 mya).

Apalharpactes, consisting of two species in Java and Sumatra, has only recently been accepted as a separate genus from Harpactes.

Outside of South East Asia and the Caribbean, however, trogons are generally absent from islands, especially oceanic ones.

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.

Their legs and feet are weak and short, and trogons are essentially unable to walk beyond a very occasional shuffle along a branch.

The strong bill is short and the gape wide, particularly in the fruit eating quetzals, with a slight hook at the end.

The New World trogons similarly have green or deep blue upperparts but are more varied in their lowerparts.

The calls of trogons are generally loud and uncomplex, consisting of monosyllabic hoots and whistles delivered in varying patterns and sequences.

Among birdwatchers and biologists it has been noted that "[a]part from their great beauty [they] are notorious ... for their lack of other immediately engaging qualities".

[13] Trogons feed principally on insects, other arthropods, and fruit; to a lesser extent some small vertebrates such as lizards are taken.

The three African trogons are exclusively insectivorous, whereas the Asian and American genera consume varying amounts of fruit.

[4] The most commonly employed foraging technique is a sally-glean flight, where a trogon flies from an observation perch to a target on another branch or in foliage.

Males attract females by singing,[4] and, in the case of the resplendent quetzal, undertaking display flights.

[15] Nest cavities can either be deep upward slanting tubes that lead to fully enclosed chambers, or much shallower open niches (from which the bird is visible).

In the case of nests dug into tree trunks, the wood must be strong enough not to collapse but soft enough to dig out.

Trogons have been observed landing on dead tree trunks and slapping the wood with their tails, presumably to test the firmness.

These are round and generally glossy white or lightly coloured (buff, grey, blue or green), although they get increasingly dirty during incubation.

Trogons are nevertheless popular birds with birdwatchers, and there is a modest ecotourism industry in particular to view quetzals in Central America.