Researchers from the University of Minnesota's Fisheries and Wildlife Department have been researching the health benefits that 1,500 miles of migration has on the monarch population. Their study has shown that the migration actually helps to rid the monarch butterflies of parasites. This implies that disruptions to migrations, whether by habitat loss, loss of nectar plants along the migration route, climate change, or other factors, can reduce the fitness of monarchs, other migrating insects, and even vertebrates.
"We've shown that migration provides an opportunity to escape from habitats that might build up levels of diseases, and also to cull out susceptible individuals," says Karen Oberhauser, a University of Minnesota Monarch researcher.
Check out the UMNews article for more details on monarch butterfly research at the U of M.