High Elevation Habitats are Important to North American Migrant Birds
Most of what we know about birds in high elevation habitats is about their breeding behavior. Because high elevations are relatively inaccessible, birds in high elevations are not well studied.
While only six varieties of birds live exclusively in high altitude habitats, over 55 bird species breed across wide elevation gradients (up to 4000 m). Birds, however, engage in three types of seasonal high elevation habitat use; not only for breeding. 1) They fly over them and may stop to rest in them when migrating. When migrating north to south (or less often when migrating south to north) many birds will stop in high elevation habitats to refuel. Colder temperatures and a later start to the growing season mean that insects and plants may be more abundant in fall, than they may be at lower elevations. If a bird migrates through these regions at these times, there is much to eat. 2)Some portion of a species that can be found at many elevations use a high elevation for breeding. They adopt a slower lifestyle in which the birds are bigger than individuals of the same species at low elevation, and both they and their offspring live longer. Their annual productivity each year, however is lower as they only have time to produce one brood/year. 3) They use them in post-breeding season for neither breeding nor overwintering. This type is characterized as “post-breeding dispersal.” They may be using the area to molt, or to prepare for winter.
By engaging in a four year long survey of birds at 10 sites in British Columbia during the post-breeding and fall migration periods (Aug-Oct), W. Alice Boyle and Kathy Martin hoped to find out more about the importance of high elevation ecosystems to regional biodiversity in the mountainous areas that cover 24% of land in the world, as well as global biodiversity. They were able to detect “a remarkable diversity of birds (95 species in 30 families) using alpine, subalpine, and montane forest, many of which used these habitats seasonally,” (461). One quarter of these birds are on lists of conservation concern.
Boyle and Martin also found great diversity in the density of bird populations, and the variety of different birds using the same locations in the various locations they surveyed. The biggest differences were between the western slope of the Coast range and other ranges in British Columbia.
Many of the birds that do breed in a wide variety of elevations are declining in number in their low elevation habitats. About 35% of North America’s breeding bird species use high elevations for at least one critical period of their annual life cycle – breeding, migration or winter. Conservation of these birds, therefore, is dependent on conservation of these high altitude habitats.
These fragile alpine and other high elevation habitats are increasingly threatened by local, regional, and global human-caused disturbance.
This is a summary article authored by Chenoa Sly. For further information, please see the original published research:
The conservation value of high elevation habitats to North American migrant birds
Boyle, W.A., and K. Martin
Biological Conservation 192: 461-476 (2015)