Altitudinal migration

[5][6][7] It is commonly thought to happen in response to climate and food availability changes as well as increasingly due to anthropogenic influence.

[5] 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.

Ungulates that have been observed to migrate altitudinally include roe deer, bighorn sheep, and mountain goats.

[5][23] There are many hypotheses for why altitudinal migration may occur, including correlations between food abundance and nutrition-the need to migrate in order to meet specific needs associated with varying abundance and nutrition; reproduction-breeding sites being at elevations different from those of non-breeding sites; anthropogenic-species being increasingly driven to higher altitudes due to human actions.

[1] Some frugivorous birds, such as white-ruffed manakins (Corapipo altera) migrate to higher elevations to exploit peaks in fruit abundance.

[24] Evidence supports the possibility that migrants have a competitive advantage compared to non-migrant (sedentary) species, due to increased foraging ability over a larger area, resulting in greater food and nutrient uptake.

[1] It's been shown that diet differs between non-migratory and migratory species in large-scale analyses and species-pair comparisons of frugivorous tropical birds.

[15] While this hypothesis is supported, and has been the most accepted, it fails to explain why altitudinal migrants return to lower elevations, or if it is done in response to shifting food resources.

[2] A number of species engage in movement that could be defined as altitudinal migration as part of their mating or reproductive behaviors.

For example, in male white-ruffed manakins, migratory behavior has shown to lessen social status and mating success at leks the following breeding season.

[26] Of the 16 species of neotropical raptors (including the Andean condor Vultur gryphus), that are known to be altitudinal migrants, most breed in the high Andes and migrate to lowland areas during non-breeding seasons.

[29] Because of this, changes in climate and seasonality (decrease or increase) would affect a large portion of tropical species and have the potential to cause a trophic cascade on the community-level.

[26] This has been seen occurring by looking at the average time of arrival and departure at high altitude areas for the American robin (Turdus migratorius).

The average time interval has shifted by as much as two weeks due to the change in seasonal patterns of resource abundance and temperature.

Some species can cross cleared lands, such as pastures, but many require closed forest areas, such as what is provided by these migration corridors.

Bighorn sheep migrate between high mountains, where they are safer from predators, and valleys where there is more food in winter.
The white-ruffed manakin ( Corapipo altera ) is a well known altitudinal migrant. Third year male (left) and After Third Year male (right).
Hawaiian geese, also known as Nene