Michigan researchers study hawks in migration hot spot the Mackinac Straits

• The narrow spot where Lake Michigan and Lake Huron come together is a popular crossing for birds of prey, which prefer to fly over land
• GPS transmitters are being strapped to red-tailed hawks to learn where they breed and spend winter
• The birds are breeding farther north than was previously suspected

Nick Alioto and Josiah Gritter were sitting in a small camouflaged shack in a field in Mackinaw City, trying to catch some raptors — specifically, hawks.

“It’s similar to fishing,” Alioto said.

The pair are researchers. Alioto is a doctorate student at Michigan State University who’s partnered with the nonprofit Mackinac Straits Raptor Watch. Gritter is a recent graduate of the University of Wisconsin-Stevens Point, working as his assistant.

To lure in hawks, they use two live birds, each harnessed to a string. The bait birds, which Alioto said usually make it out unharmed, work in shifts so they don’t get too tired out. A pigeon and a starling were on duty. 

From inside the blind, Alioto and Gritter periodically pulled the strings and the birds out in the field flapped their wings and hopped up and down. To try to further attract hawks, speakers near the starling played a stress call.

“They hear something that’s stressed, looks injured, it’s more enticing,” Alioto explained.

‘They don’t like to cross water’

The researchers are set up near the Straits of Mackinac because the waterway is a major crossing for raptors, the term for birds of prey such as hawks, eagles, owls and falcons. 

Mackinac Straits Raptor Watch has more than a decade of data showing how many birds of prey come through the area, where Lake Michigan and Lake Huron come together at a narrow point. In 2019, the nonprofit counted a migration of 22,420 such birds, a North American record for the largest crossing of red-tailed hawks in a single season. 

While Alioto catches and records information from a variety of hawks, his main research project is specifically looking at the migration patterns of northern red-tailed hawks. 

“For red tails, they don’t like to cross water,” Alioto explained.

Raptors like red-tailed hawks use pockets of warm air — or thermals — to rise up without flapping their wings. That enables them to save energy while migrating. Because thermals form better over land than water, going through Michigan and then crossing at the narrow Straits of Mackinac makes for an easier journey.

“It’s a funnel,” Alioto said. “They can use thermals and then get to the shortest water crossing here, which is easier to cross than trying to cross over a whole lake or going completely around.”

Though red-tailed hawks are thought to be the most common hawks in the United States, Alioto said, before he started his research four years ago, not much was known about them.

“We knew they migrated. Nobody knew anything else,” he said. “And so I figured this was the perfect opportunity to study this population here, where we know there's just a huge number of them coming through.”

If Alioto and his team catch an adult red-tailed hawk and it looks strong and healthy, they strap a GPS transmitter to it like a little backpack. The solar-powered transmitter periodically tracks the bird’s location and other information like altitude, flying speed and the air temperature. The GPS transmitters use cell phone networks to send over data. If the birds fly into areas with no cell coverage, like in certain parts of northern Canada, the units store the data and send it when the birds return to an area with cell service. 

At one point, a bird didn’t send any data for two years, so Alioto thought it had died. But then the bird came back into cell range and uploaded 56,000 GPS points. 

“It was really exciting,” Alioto said.

Through his research, Alioto’s learned that most of the northern red-tailed hawks that come through the straits spend their winters in Michigan, Illinois, Indiana, Ohio, Tennessee, Alabama and Kentucky. He’s learned that the younger birds are more likely to vary their migration patterns, while the adults tend to stick to the same route. And Alioto said he was surprised to learn the population is breeding in Manitoba, Ontario and Quebec, in regions farther north than was previously thought. 

“These birds are actually going into sub-Arctic areas — Hudson Bay lowland, the Boreal Forest — so they’re going a little farther north, which is really interesting,” he said. “We didn’t expect all of them to do that.”

They catch a ‘sharpie’

Back at the blind, Gritter grabbed his binoculars. There was a hawk nearby.

“It’s sort of coming in our direction,” he said, quietly.

“He looks like he’s interested,” Alioto responded.

Seconds later, the hawk swooped down in the direction of the starling. Alioto started saying, “Go, go, go, go, go!” and Gritter sprang into action, flying out of the shack, hoping to catch the hawk before it flew away.

The hawk left the uninjured starling on the ground and flew into a vertical net propped up nearby like a backstop. Gritter grabbed onto the hawk, holding it by its legs and tailfeathers, and gently began untangling it.

Gritter and Alioto then took the bird into the blind to assess it. They said she was a female sharp-shinned hawk, or “sharpie,” at least 2 years old. Though she wasn’t a red-tailed hawk, they still took advantage of the opportunity to gather scientific data about her, some of which can be used by research partners.

To weigh her without her trying to escape, they gently slid her into a tennis ball canister, which she placidly accepted.

Next, Alioto explained it was time to say “night, night.” They started putting a hood on her, a little leather bonnet that covered her head and eyes. Once the hood was secured, she stood up straight with a puffed out chest and looked like she was proudly showing it off.

“There she is, nice and calm,” Alioto said.

They weighed her, measured her and checked her for parasites and added a little metal band to her ankle. Then she was released back into the wild.

Further research

After Alioto gets his Ph.D., he has his eyes set on becoming the research director at the Mackinac Straits Raptor Watch. If that ends up being the case, he’d like to create a Michigan migration network that would ideally collaborate with other groups like the researchers at Whitefish Point Bird Observatory in the Upper Peninsula, other Michigan Audubon projects and universities.

“So that's the end goal, hopefully, to have this big, comprehensive network that covers all sorts of migrants coming through Michigan … because Michigan is such a migration hotspot,” he said.

As for his red-tailed hawk research, Alioto said it’s important to study birds while they are still common, rather than waiting until they become endangered or threatened.

“So by getting this information now, we're better prepared for any threats they do face,” he said.