PELLSTON, Mich. — The only living descendants of dinosaurs are extremely faithful to their nesting sites.
“Birds are mind-bogglingly good at going back to the same tree year after year,” said Matt Hack, a graduate student researcher stationed at the University of Michigan Biological Station for the last three years during breeding season.
The evolutionary superpower of navigational accuracy over hundreds — even thousands —of miles and the meaning behind it is a mystery that a University of Michigan-led research team is working to decipher.
For field work, that innate geographical precision combined with lightweight tracking technology makes the process of catching, releasing and recapturing the same birds much easier than finding a needle in a haystack.
However, the work can be challenging because if the birds move even one kilometer to a new territory, they are nearly impossible to find again.
“It only took us two days to find our first one this year,” Hack said. “We went to the GPS point and there was the bird.”
A Window into the Avian World
Hack is a Ph.D. student in the laboratory of Dr. Ben Winger, a professor in the U-M Department of Ecology and Evolutionary Biology and curator of birds in the Museum of Zoology in Ann Arbor.
Based each spring at the research and teaching campus in Pellston, the team is deploying and successfully recapturing lightweight geolocators attached like mini-backpacks on a suite of migratory songbirds that breed in the boreal forests of northern Michigan.
“Songbird migration is very difficult to observe in real time because the birds are small and they usually migrate at night — unlike, for example, a ‘V’ of geese that you can watch overhead,” Winger said. “To understand exactly where an individual migratory bird goes throughout the year and how it gets there, we need to attach a tiny geolocator tag and recapture the bird again a year later. This provides richly detailed insights into the extraordinary annual journeys of these birds, many of which are experiencing steep population declines.”
Hack’s dissertation work is focused on factors that shape bird range and distribution.
Hack is leading a team of student researchers that set up sites on the more than 10,000 forested acres at UMBS and surrounding state and national forests. Max Witynski, another Ph.D. student in Winger’s lab, also is leading a team doing similar research in the Huron Mountains of the Upper Peninsula.
Their tiny technology tracks the seasonal migration of a variety of species including White-throated Sparrow, Dark-eyed Junco, Swainson’s Thrush, Red-eyed Vireo, and Yellow-rumped Warbler.
Birds of a Feather
The researchers are curious whether all birds of the same species that are UMBS breeders end up in the same place in the winter or if it’s more scatter-shot.
“A huge diversity of songbirds breed in this same habitat each year — a place that fits their similar needs and requirements to live and survive — and then they migrate to wildly different destinations for the winter,” Hack said. “One decides to go to Ann Arbor and another goes all the way to South America. Why do we see such different migratory strategies? We want to know why birds may be in sync for part of the year and completely out of sync for other parts of the year.”
In spring 2025 the researchers recaptured 12 sensors on songbirds that were attached the previous year to track movement.
Last year the team recovered 16 tags.
“We’ve been a little worried about the ice storms this March and the amount of damage that caused to the habitat,” Hack said. “It has been pretty quiet in the woods this year with fewer birds singing overall and a lot of trees and branches down. On the flip side, it’s always kind of incredible that this ever works at all.”
Advancing Knowledge of Evolution
At first look, some of the tracking devices seem to show two ends of an extreme.
Some of the shorter-distance migratory birds chose a destination in the central United States.
“A Dark-eyed Junco spent its winter in southern Ohio and a Hermit Thrush was based in Kentucky,” Hack said.
Of the long-distance migratory species, some go all the way to the Andes mountains.
“We had multiple Swainson’s Thrushes go to essentially the same part of the Andes in northern Peru,” Hack said, “so thousands of miles and yet they never really diverge at any point in the year from each other.”
He also said the Red-eyed Vireos seem to be going to the Amazon basin in northern South America.
However, the researchers need to see more data to begin to identify trends.
What they collect will help them understand how the different distances the birds migrate render into differences in how they allocate their lives — what humans might refer to as time management, setting priorities and emergency preparedness.
“Migration and the distance of migration could translate into some real evolutionary differences between these birds,” Hack said. “Long distance migration might translate to less time spent investing in breeding and more time being in high-quality tropical winter grounds and surviving.”
And vice versa.
Short distance migration could be a trade-off of having more time in the breeding grounds to find a mate and nest their eggs with extra room to try again if something goes wrong.
“But they’d spend the winter in a place with a temperate climate, which has its disadvantages,” Hack said.
That’s the hypothesis about shared destinations that remains under investigation.
Geolocator Technology
The geolocation devices weigh as little as 0.3 grams — necessary for small birds that weigh less than a ping pong ball.
The devices have been used for several decades by ornithologists and are known to be safe for the birds when used properly.
A larger species like a thrush can carry a tag with just enough battery to record GPS coordinates once a week. A smaller species like a warbler cannot carry a tag with GPS technology, so the team uses even lighter tags that record daily sunrise and sunset times and atmospheric pressure, which together provide an estimate of location.
The songbird tags are too small to be able to transmit data, so the researchers must capture the bird again the following year, which is possible when the bird returns to its same territory to breed again.
Hack plays recorded songs to lure birds to the mist nets he sets up in the forest. After catching a bird, he quickly attaches or removes the geolocator, examines the bird’s health and condition, and bands a leg with a uniquely numbered metal band and colored plastic band for identification and monitoring.
To access a geolocator’s data compiled over the bird’s flight route in the past year, Hack removes the device from the bird and downloads the data into a computer, putting it through elaborate coding scripts.
After field season, Hack will go back to the Ann Arbor lab and download and analyze all the data collected.
Supporting Discovery
The 2025 fieldwork is Hack’s close-out season at UMBS.
The ongoing research from the Winger Lab at U-M has been supported in part by the National Science Foundation (NSF) and the U-M Biological Station.
“UMBS has given me full fellowships to live and research here the past three summers, which has been incredibly helpful,” Hack said.
His time at the Biological Station studying birds as a graduate student closes a chapter in his life that started when he was in high school.
That’s when he first dipped his toes into the experience of living and learning at the historic campus nestled along Douglas Lake.
“I had a teacher at Ann Arbor Community High School who was an alum of UMBS. She ran an ecology club I was in, and she brought all of us here two winters in a row for a ski and snowshoe retreat,” Hack said. “I learned what UMBS was before I was in college. It’s bittersweet to be here to finish work that will go into my Ph.D. dissertation at the University of Michigan.”
“UMBS has been the perfect location for us to pursue this research, as the team has close access to so many kinds of habitat and a supportive community and campus to return to after a long day of fieldwork,” Winger said.
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