Birds have the ability to migrate across national and international borders - the Arctic tern holds the record for longest migration distance, traveling over 40,000 miles from Greenland to Antarctica! Birds can migrate short distances, moving from higher to lower elevation on a mountainside; medium distances, spanning from one to several states; and long distances, such as the Arctic tern flying from one pole to the other. Species that don't migrate are known as resident birds.
Image: West Nile Virus transmission, Thurston County WA Public Health and Social Services.
During migration birds can be infected with parasites and diseases, such as malaria, cholera and influenza. Bird migration can help diseases spread globally. Cases of West Nile virus were first reported in the New World in August of 1999 in Queens, New York. Unusual bird deaths were reported at the Bronx Zoo and in adjacent areas, followed by human infections. The first case of West Nile virus was isolated from the blood of a woman in the West Nile region of Uganda in 1937. Migratory birds are the suspected vehicle for the introduction of the West Nile virus to North America, where it has spread into Latin America and the Caribbean. Weakening of birds' immune systems due to stress can contribute to the spread of diseases and parasites during migration - so can climate change.
Warming temperatures have altered the geographical distribution of many species, including birds. Some bird species ranges in North America and other areas of the Northern Hemisphere have shifted north as warming temperatures make northern latitudes more hospitable to species typically found farther south. The shift in bird ranges is an opportunity for parasites and diseases to infect new areas and resident birds. In the Czech Republic, warmer temperatures have changed the distribution of birds carrying tick-borne encephalitis, spreading the parasite into higher altitudes. Native and threatened birds also risk contracting new diseases, such as the Galapagos penguins, which are now infected by malaria parasites. Migratory birds are the suspected vehicle for the introduction of malaria into the Galapagos Islands, where the parasite had not been previously present. In the United States, scientists established for the first time that malaria parasites are able to complete their life cycle in the North American Arctic. The study in Alaska detected malaria infected birds as far as 64°N, causing concern that local birds may be exposed to new parasites with warming temperatures.
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