Altitudinal migration

Altitudinal migration is a short-distance animal migration from lower altitudes to higher altitudes and back. It is commonly thought to happen in response to climate and food availability changes as well as increasingly due to anthropogenic influence. These migrations can occur both during reproductive and non-reproductive seasons. Altitudinal avian migration is common, and can also be found in other vertebrates, and can be seen in some invertebrates.

Typical characteristics of tropical altitudinal migrants include: a high rate of frugivory or nectarvory; movement between lower elevation areas during non-breeding seasons and higher elevation areas during breeding seasons, or on a consistent annual or seasonal cycle; at least part of the population being migratory with a possible portion of the population residing at breeding sites year-round. This last characteristic can be sex-biased, as it is with juncos, in which the males are less likely to migrate than the females. The white-ruffed manakin provides a good example of an altitudinal migrant by displaying all of these traits. It has a high rate of frugivory, migrates from lower elevations to higher elevations on a predictable breeding-season based cycle, and part of the population is migratory, with a small portion possibly remaining at the breeding sites year-round.

There are many documented examples of migratory range shifts along an elevation gradient among temperate species. While these migrations are more understood in temperate regions, and far less understood among tropical ecosystems and species, there are documented cases. Altitudinal migration is typically seen among taxa found in montane areas. Generally, as elevation increases, the species richness decreases.

In the tropics, altitudinal migrations are most commonly seen among frugivores or nectarvores, such as what is seen among tropical hummingbirds, which migrate altitudinally in response to shifts in food abundance and availability. This migration pattern has been observed in neotropical birds, but has also been seen in other terrestrial, tropical montane species such as Baird's tapir and white-lipped peccary.

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