Variations in migration patterns are numerous. Some species move only a short distance like from the Upper Peninsula to mid-Michigan. Others will travel hundreds or even thousands of miles, some over vast bodies of water or tracts of inhospitable terrain. Song Sparrows that breed in Michigan may migrate to the southeastern United States, or may remain a year-round resident. They are "obligate partial migrants," meaning only part of the population migrates annually.
There is still a lot of unknowns about migration. A recent study found that migratory birds aren’t picky about their rest stops. Birds that travel thousands of miles between nesting grounds and wintering grounds twice each year, sometimes just need a place to stop. As forests have been cleared for development, birds have to find sanctuary in whatever forest, woodlot, or yard available when they become too tired or encounter bad weather on their journey. And if they choose your yard to stop over, hopefully you’ll have fresh water, food, and shelter to make their journey a little easier.
- Study finds migratory birds not picky about their rest stops: http://news.uns.purdue.edu/x/2009b/090812DunningStopover.html
- Bird banding recovery data to document migration behavior in Song Sparrows: http://elibrary.unm.edu/sora/NABB/v024n04/p0122-p0128.html
- WBU Educational Resources on Bird Migration: http://www.wbu.com/education/birdmigration.html