Wisconsin Department of Natural Resources
101 S Webster, P.O. Box 7921, Madison, WI 53707
Phone: 608-267-2773 TDD: 711
CONTACT: Sumner Matteson, 608-266-1571;
Fred Strand 715-372-8539 ext. 120
SUBJECT: High tech tracking to unlock secrets of endangered bird’s travels; On the longest day of the year, answers from an endangered seabird
SUPERIOR – Just what does a state endangered seabird do on the longest day of the year?
State avian ecologists and their partners will get the definitive answer this year. Just in time for the summer solstice, they have outfitted 15 common terns with tiny devices that use daylight hours to help detect and record the birds’ locations and whether they are in water.
The so-called “geolocators” will be calculating and recording the locations of the common terns every five minutes, eventually giving the Department of Natural Resources and partners very specific information about where these birds go and when, says Sumner Matteson, a DNR avian ecologist.
“The geolocators give us the opportunity to understand the birds’ migratory routes, where they stop over, and where they spend the winter,” Matteson says. “We’ll get a greater understanding of their ecology and can work proactively with partners in states and countries along the way to aid the species.”
DNR has been banding common terns since the mid-1980s as part of a recovery plan for the species, which is listed as endangered in the state.
Based on records from the capture and identification of birds outfitted with the metal leg bands, DNR knows that Wisconsin breeding birds have wintered in Guatemala, El Salvador, Colombia and Peru. “But we don’t know where they stopover and where they stage,” he says.
To get specific answers, Matteson and DNR wildlife manager Fred Strand last week joined with scientists from the Natural Resources Research Institute in Duluth, Minn.
Strand and Matteson trapped and banded 15 adult birds at Interstate Island in the Duluth-Superior Harbor and outfitted the birds with geolocators.
Geolocators are the smallest known devices capable of detecting and logging the locations of birds. These light-sensitive devices use changes in ambient light levels to estimate the times of sunrise and sunset from which latitude and longitude can be calculated, Matteson says.
The operation last week marks the first time geolocators have been used on common terns in the Midwest, and ecologists were able to capitalize on improved technology since the first geolocators were used on seabirds on the Atlantic Coast in 2007, Matteson says.
The devices have become lighter and gained features, making them better for the birds and the researchers, Matteson says. The geolocators used at Interstate weigh 1.1 grams; they record a maximum light level every 5 minutes for 1 year. An added feature known as a “wet-dry sensor” records whether the bird is wet or dry every 10 minutes whenever a tern is in water for a period greater than 3 seconds, Matteson says.
The birds outfitted with geolocators were nine years old or younger and had a track record of returning to Interstate Island, both factors that make them a good bet to return and be recaptured. After trapping a bird and checking its age from a log maintained by Strand since 1989, selected terns were handed off to NRRI scientists Gerald Niemi and Annie Bracey. Those scientists outfitted the bird’s leg with the geolocator and measured, weighed and collected blood samples for DNA analysis before releasing the bird.
In the coming weeks, Bracey and Strand will be monitoring closely the adults outfitted with geolocators. A year from now, when the terns return in spring to Interstate Island, the “geolocator terns” will be trapped and the geolocators removed so that the all of the data can be downloaded and decoded, using specialized computer software, Matteson says.
“The exciting part will be one year from now when we see how many of the outfitted birds come back,” he says. “Because of high colony site fidelity, chances are that most of the 15 adults will survive their long migrations to Central and South America and return to their Lake Superior home in the harbor.”
The geolocator project is part of a much larger effort – the Great Lakes Common Tern conservation initiative led by the University of Minnesota. The geolocator project also involves the U.S. Fish and Wildlife Service, which provided major funding, DNR, Lotek—the company that produced the geolocators, and the U.S. Breeding Bird Laboratory, which authorized the project.
Populations of common terns in Wisconsin and elsewhere in the Great Lakes have decreased as a result of habitat loss. The bird also continues to be vulnerable to pesticide contamination, Matteson says.
The bird prefers sparsely vegetated sites, which historically have been occupied or disturbed by people. Today, DNR manages four main sites for common terns: the Interstate Island site and one near Ashland, one in Lake Winnebago, and a site on Lake Butte des Mortes created with funds through the natural resource damage assessment process stemming from historic PCB releases on the Lower Fox River and Green Bay. The Lake Superior sites constitute the biggest populations, with 200 to 300 breeding pairs recorded at the Interstate Island site and between 100 to 130 breeding pairs at the Ashland site in recent years.