HARSENS ISLAND, MICH. -- For something so small and still flightless, black tern chicks are notoriously difficult to catch.
At the sight of any perceived threat -- say, a kayak carrying a well-intentioned researcher from Audubon Great Lakes -- the chicks will scuttle off their nests and swim into the surrounding coastal Michigan marsh, where they can practically disappear under lily pads and within grasses, their mottled brown juvenile plumage providing the perfect camouflage.
Despite the chicks’ best efforts to evade attention, though, this year more than two dozen were captured and successfully affixed with tiny tracking devices called NanoTags to help researchers understand why black terns -- elegant yet secretive marsh birds -- are mysteriously disappearing from Michigan.
A black tern nest. Photo by Erin Rowan, courtesy of Audubon Great Lakes
Audubon Great Lakes and partners have been closely watching Michigan’s black terns for nearly a decade, monitoring nests and banding adults in an attempt to piece together the puzzle of the black terns’ 70 percent decline over the past 50 years. Outfitting chicks with NanoTags is a newer initiative in those efforts -- one that aims to collect data on fledging success, to further fill in the big picture and help shape future conservation strategies.
“Black terns face an uncertain future in Michigan,” says Erin Rowan, senior coordinator, Michigan Conservation for Audubon Great Lakes. “By tracking whether black terns successfully fledge and depart their breeding grounds, we can better understand whether the cause of their population decline is from low chick productivity or low adult survivorship.”
A Motus tower at Wigwam Bay State Wildlife Area. These radio telemetry towers are part of an international network that helps researchers study migratory animals, such as black terns. | Photo by Erin Rowan, courtesy of Audubon Great Lakes
Black terns are charismatic, communal creatures that spend the summer months breeding in colonies across the northern United States and Canada. Michigan is home to several significant nesting sites for these agile birds, with two of the largest colonies found in the St. Clair Flats State Wildlife Area near Detroit and Wigwam Bay State Wildlife Area, north of Bay City.
This summer, researchers and volunteers boated into these marshy, difficult-to-reach locations, where they managed to scoop up and tag 28 chicks. The tags beam signals to special towers as part of the Motus Wildlife Tracking System, an international network using radio telemetry to study migratory animals, allowing researchers to monitor the terns as they wrap up their Michigan summers and make their way to wintering grounds along the coasts of Central and South America.
The first two seasons of tagging, over 2019 and 2020, coincided with nesting sites being plagued by historic high water levels on the Great Lakes. Lower detection rates of tagged chicks for those years had researchers worried about the species’ ability to fledge their young. But preliminary data from this year’s class of tagged chicks has eased some concerns, Rowan says: So far, 13 of the 28 chicks have been redetected away from their colonies, which is “a really good initial response.” This suggests that the young birds are indeed successfully leaving their nests for the next chapter of their lives.
“This is the first time a study like this has been done on pre-fledged black tern chicks, so there were some growing pains,” she says. “All the data still needs to go through a more thorough clean-up process this winter as well, but initial results seem to support that they are successfully producing young here in Michigan.”
In the coming months, the NanoTag data will be analyzed and combined with additional research to help create a population model for Michigan’s black terns. The hope, Rowan says, is that the model will eventually steer conservation efforts, which could have implications for these unique birds as well as for the Michigan landscapes they call home.
“Black terns, similar to other secretive marsh bird species, are really great bioindicators of habitat quality,” she says. “They are also a really enigmatic species. Our hope is that this model is going to help determine the cause of the regional decline.”
A banded, tagged adult black tern. U.S. Geological Survey regulations state that tags and leg bands, combined, must weigh no more than 2% of a bird’s body weight so as to not impact a bird's survival or ability to fly.| Photo courtesy of Audubon Great Lakes
Many people may never see this elusive bird in person, but anyone in the world can see the pathways that tagged black terns follow by checking out the Motus Tracks database and selecting “map” to view their movements.
Learn more at gl.audubon.org.
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