Stravers reflects on 40 years of raptor research

By Audrey Posten, North Iowa Times

“We’re all fond of raptors—their beauty, the way they rise and lift up, their strength and boldness.”

But for ornithologist Jon Stravers, that fondness goes back four decades. “Hawkman” has been researching hawks and other raptors—the birds of prey known for their hooked beaks, sharp talons and keen eyesight—since the mid-1970s. He shared some of his experiences Saturday, during a presentation at the 35th annual HawkWatch, an event hosted by Marquette’s Driftless Area Wetlands Centre, in partnership with the Upper Iowa Audubon Society, Raptor Resource Project and Driftless Area Bird Conservation, to celebrate the fall migration of raptors and other birds along the Mississippi River Flyway.

Stravers pays tribute to Gladys Black, known as the “Bird Lady of Iowa,” for his break into the field.

“She’s an avid birder and campaigner against pesticides, and always eternally vigilant about protecting birds,” he shared. “I became a student of hers, and she taught me quite a bit and really influenced my life.”

His experience with Black led Stravers to work with a state ecologist who was conducting raptor projects in northeast Iowa.

“Once I got wind of the work and what it was like, I’ve been doing it ever since,” he said.

Research began at Effigy Mounds National Monument in the early 1980s, then moved to an area north of the park, near Luster Heights, not long after. 

“We started the day-to-day monitoring of raptors, and I had a crude, little station on top of the hill,” Stravers recalled.

From 2001 to 2012, he operated mostly from the Smokey Hollow Road area near Effigy Mounds.

“But for some reason, that place got plowed up and turned into a corn field,” he said.

In the past several years, Stravers has worked near Decorah, on a project sponsored by the Raptor Resource Project and Luther College. It gives students a good opportunity to learn about raptor biology and migration, he noted.

Just this year, Stravers added a station south of Pikes Peak State Park, near McGregor. He had hoped to operate it on Saturday, bringing migrating raptors captured at the site to the Wetlands Centre for HawkWatch attendees to view. Unfortunately, rain thwarted the efforts.

Fall, particularly the time from September to mid-November, is an important period for raptor research. 

“Birds are always moving from one spot to another and doing interesting things. It’s a time we can capture birds that are migrating. We use pigeons to lure them in,” Stravers explained. 

Red-tailed hawks are one of the most common birds Stravers captures, and his personal favorite is the red-shouldered hawk. But during migration, you can see birds you might not expect, he added.

The Driftless Region plays a unique and important role in migration.

“These valleys capture the cold air over night and then, on a normal day, the sun heats these pockets of air. When the air gets heated, then it rises out of the valleys,” Stravers detailed. “So throughout our region, when the raptors are coming in the middle of the day, they come along these valleys and there’s an uplift. We can’t see it, but the birds can find it and they ride that and circle in these thermal currents that help them do the work of migration. It aids them along.”

In the 1980s, the Iowa Department of Natural Resources, along with Effigy Mounds, the Fish and Wildlife Service, Upper Iowa Audubon and several other groups, engineered HawkWatch weekend to celebrate the Driftless Area’s role in the migration.

“At Effigy, we’d do programs outside on the lawn, and that went on for years. A lot of people came from all over,” said Stravers.

Several years ago, the Wetlands Centre took over the event, holding it on the traditional first Saturday of October.

“I’m glad the Wetlands Centre has allowed us to keep this event alive,” he reflected.

Migration isn’t the only prime research time for Stravers, though. The work spans all seasons, he said, and is most important when the birds are nesting in the area.

Before that even begins, the birds go through an elaborate courtship ritual Stravers has dubbed the “rouge of red shoulders.”

“They have a pre-courtship communal gathering, which I haven’t found anything in literature on, but it happens,” he explained. “You come in on this thing and there’s like five or six or eight red shoulders all in one spot, and there’s all kinds of calling, all kinds of bumping and interchange. The first time I saw it, I thought, ‘What the heck is going on here?’ I didn’t understand it.”

“Over the next few years, I see it again. Then I started to understand this does not happen after they start the nesting cycle. It’s only before everybody has the nesting territories divvied up,” he continued. “They get together and it’s like a dating service. Some of their mates didn’t survive, or they may want to trade one in, so they have this social gathering.”

By late March, the hawks have laid their eggs, which incubate, then hatch near the end of April. The babies spend around 40 days in the nest before they “branch.”

“They don’t really get up and leave. They move around the neighborhood of the same tree for a week or two,” said Stravers.

The data Stravers and his colleagues gather through monitoring is added to data collected throughout the country. 

“We’re doing it here as much as we can, but we’re also involved with Hawk Watch International that monitors sites around North America,” he said.

The data helps researchers understand bird populations—how many nests there are, how the birds are traveling, what they’re eating and how they adjust to climate change.

“Some things we don’t fully understand,” he admitted, “but by monitoring, there may be things we can do. Birds are sensitive; our raptor populations are a litmus paper of the environment.”

In his time in northeast Iowa, Stravers said he’s watched the number of hawk and eagle nests in the area explode, rebounding from the ravages of DDT. 

“When I started working in raptor research in the mid-1970s, there was only a single active eagle nest in the entire upper river. Then, slowly, it became six or seven, and then it became several dozen, and then it became wow,” Stravers remarked. “Now, it’s in the hundreds. Within 10 minutes of here there are at least 10 active eagle nests on the river.”

“It’s really a remarkable recovery story,” he added, “but it’s also one of those things that needs eternal vigilance.”