The birds that keep coming back: How U-M read migration in 1,600 songbird genomes

Why do some songbirds fly from Michigan to the Amazon every year while others stop in Tennessee? And what does that choice do to a species over millions of years?

Ben Winger, associate professor of ecology and evolutionary biology and curator of birds at the University of Michigan Museum of Zoology, studies the evolution of bird migration. His lab's research is turning a long-held assumption inside out.

Scientists once assumed that birds capable of flying thousands of miles must also be good at settling in new places. If a warbler can reach South America, surely it can find a different patch of forest to nest in. Winger's team tested that idea by sequencing more than 1,600 genomes from 35 boreal bird species collected across 3,500 kilometers of forest, from Alberta to Nova Scotia. The genomes said the opposite. Long-distance migrants return to the very same places to breed, year after year, which means their populations are far more genetically distinct across North America than anyone expected.

Then came the surprise. The farther a species migrates, the more genetic diversity it carries. Birds that winter deep in the tropics have healthier genomes than close relatives that spend the winter in Michigan. Winger's team believes this is a signature of survival: despite the risks of migration, birds that reach the tropics find a good environment with abundant food and survive at higher rates, keeping their populations stable over evolutionary time.

That finding matters now. North America has lost nearly 30% of its birds since 1970, and long-distance migrants are among the steepest decliners. What the genomes reveal is a survival strategy tuned over millennia that is failing in a rapidly changing world.

To understand why, the Winger Lab combines three approaches: population genomics, geolocator tracking that follows individual birds through a full annual cycle, and the historical collections of the U-M Museum of Zoology, where specimens gathered in the 1800s can now yield DNA showing how bird populations weathered the Great Lakes logging boom more than a century ago.

Doctoral students Max Witynski and Matt Hack lead NSF-funded fieldwork at the University of Michigan Biological Station and in the Huron Mountains, fitting tiny geolocators to songbirds. That work has shown that Swainson's thrushes nesting in Michigan's Upper Peninsula winter in central Peru, while their close relatives the hermit thrushes travel only as far as Texas or Louisiana.

The upshot is personal. The bird singing in your backyard this spring may be the same individual that sang there last year, and the year before that, for six, seven or eight years running, returning each time from a journey of thousands of miles.

Read the full story: https://research.umich.edu/research-stories/small-birds-long-journeys/

Learn more about the Winger Lab: https://www.wingerlab.org/

The genomics study, led by former U-M doctoral student Teresa Pegan, was published in Nature Ecology & Evolution: https://www.nature.com/articles/s41559-025-02699-3

Video produced by Eric Shaw, director of digital marketing and communications, Office of the Vice President for Research at the University of Michigan.