One might assume that birds of flight are cosmopolitan travelers, and bird species should be distributed far and wide—spread across long distances and even continents. However, a study led a former University of Chicago graduate student shows that birds have strong ties to the climate patterns of their habitat. As a result, the geographical distribution of birds may be more restricted than we think.
Scrutinize the distribution of birds across the globe, and it is obvious that land birds, for example, have ranges that abruptly end at coastlines. You may not notice a similar turnover of bird species within continents, but in fact one is present at the freezing line—the boundary between the tropics and cooler, temperate areas.
As part of his PhD thesis at UChicago, Alex White, PhD’18, conducted a study that shows that despite no significant physical barriers stopping them from spreading out, bird species are strongly confined to their habitats as demarcated by the freezing line. The results were recently published in the journal Nature Communications.
Nowhere in the world does the freezing line loom as drastically as the Himalayas. But it is not the world’s tallest mountain peaks that serve as the boundaries of avian habitats and movement; instead, it is the freezing line, which cuts across the slopes at an elevation of about 1600 meters—less than a fifth of the way up to Mount Everest’s peak.
White worked with adviser Trevor Price, professor of ecology and evolution at UChicago, to examine 305 species of open-habitat and tree-dwelling birds out of the known 621 species present in the Himalayas. The numbers of species were estimated over a ten-year period from reported sightings and vocalizations across 38 sites in the Himalayan forests.