Something interesting I have received from Wild about migrations:
Migration decreases disease
August 2, 2011,
It has previously been assumed that migratory animals spread diseases from one area to another. But a recent study has suggested the opposite.
Every year animals all over the world migrate – some of them over thousands of kilometres and over many months. In Tanzania the wildebeest migration is a well-known wildlife spectacle and along South African shores the annual sardine run attracts attention.
It’s been thought that migration increases disease. Surely when animals migrate their diseases travel along with them? Research done by the University of Georgia Odum School of Ecology points to a different pattern.
In the case of some parasites, migration enables animals to escape an environment that has become infested. While the hosts are away the parasite load decreases and the animals can return to a habitat that is relatively free of disease.
Migration also exacts a physical toll and disease-ridden animals can’t survive long journeys. The result is that infected individuals are removed from the group and the most virulent strains are eliminated.
These new insights come from a study on monarch butterflies. Butterflies in cool climes like Canada migrate south to spend the winter in central Mexico. In more temperate places like Florida the monarchs don’t migrate. Researchers discovered that the parasite load is highest in the butterflies that don’t migrate and lowest in the ones that journey the furthest.
This research emphasises the importance of migration to the health of a species. Unfortunately, nowadays successful migration is hampered by deforestation and urbanisation. Many migratory routes are blocked by dams, fences and agricultural land, where livestock and migratory species are exposed to each other’s pathogens.
"Migration is a strategy that has evolved over millions of years in response to selection pressures driven by resources, predators and lethal parasitic infections,” says researcher Barbara Han from the University of Georgia Odum School of Ecology. “Any changes to this strategy could translate to changes in disease dynamics.”
S. Altizer, R. Bartel, B. A. Han. Animal Migration and Infectious Disease Risk. Science, 2011; 331 (6015): 296 DOI: 10.1126/science.1194694
Viewed online [http://www.sciencedaily.com/releases/2011/01/110120142323.htm]
Here is the source: https://www.wildcard.co.za/blog.htm?act ... st&id=2469