Altitudinal migration in the context of "Bighorn sheep"

Bird migration is a seasonal movement of some birds between breeding and wintering grounds that occurs twice a year. It is typically from north to south or from south to north. Migration is inherently risky, due to predation and mortality.

The Arctic tern holds the long-distance migration record for birds, travelling between Arctic breeding grounds and the Antarctic each year. Some species of tubenoses, such as albatrosses, circle the Earth, flying over the southern oceans, while others such as Manx shearwaters migrate 14,000 km (8,700 mi) between their northern breeding grounds and the southern ocean. Shorter migrations are common, while longer ones are not. The shorter migrations include altitudinal migrations on mountains, including the Andes and Himalayas.

Sky islands are isolated mountains surrounded by radically different lowland environments. The term originally referred to those found on the Mexican Plateau and has extended to similarly isolated high-elevation forests. The isolation has significant implications for these natural habitats. Endemism, altitudinal migration, and relict populations are some of the natural phenomena to be found on sky islands.

The complex dynamics of species richness on sky islands draws attention from the discipline of biogeography, and likewise the biodiversity is of concern to conservation biology. One of the key elements of a sky island is separation by physical distance from the other mountain ranges, resulting in a habitat island, such as a forest surrounded by desert.

The resplendent quetzal (Pharomachrus mocinno) is a small bird found in Central America and southern Mexico that lives in tropical forests, particularly montane cloud forests. They are part of the family Trogonidae and have two recognized subspecies, P. m. mocinno and P. m. costaricensis. Like other quetzals, the resplendent is mostly omnivorous; its diet mainly consists of fruits of plants in the laurel family, Lauraceae, but it occasionally also preys on insects, lizards, frogs and snails.

The species is well known for its colorful and complex plumage that differs substantially between sexes. Males have iridescent green plumes, a red lower breast and belly, black innerwings and a white undertail, whilst females are duller and have a shorter tail. Grey lower breasts, bellies, and bills, along with bronze-green heads are characteristic of females. These birds hollow holes in decaying trees or use ones already made by woodpeckers as a nest site. They are known to take turns while incubating, males throughout the day and females at night. The female usually lays one to three eggs, which hatch in 17 to 19 days. The quetzal is an altitudinal migrant, migrating from the slopes to the canopy of the forest. This occurs during the breeding season, which varies depending on the location, but usually commences in March and extends as far as August.