GRAND RAPIDS, Mich. (WOOD) — Wildlife biologists from the Wisconsin Department of Natural Resources estimate nearly 1,500 birds have been found dead along several islands in Lake Michigan — more than half of the state’s estimated population.

The likely culprit? Bird flu.

A report from Michigan Radio says entire colonies of Caspian terns were found dead or dying. Based on the early count, the Wisconsin DNR estimates that 64 percent of the state’s adult population of Caspian terns are gone.

According to the Milwaukee Journal-Sentinel, more than 1,200 adult Caspian terns were found dead on Gravel Island and Hat Island — one on either side of the Door Peninsula.

A similar die-off of more than 200 Caspian terns was found on Bellow Island in Grand Traverse Bay.

Sumner Matteson, an avian ecologist who has spent decades working with the Wisconsin DNR, told Michigan Radio it was a stunning sight.

“Absolutely devastating. Catastrophic. It’s going to take years for the Wisconsin population to recover,” Matteson told Michigan Radio. “Seeing hundreds of dead birds scattered in a line before you with others dying among those … it’s a feeling of helplessness, knowing that there’s nothing, absolutely nothing you can do for those birds.”

Wildlife biologists have discovered more than 1,500 Caspian terns killed by Avian flu across three islands in Lake Michigan. (Courtesy Wisconsin DNR)

Years could be an understatement. This large of a die-off will also impact future generations.

“No young are being produced. And then the loss of all of these adults is serious,” University of Minnesota professor Francie Cuthbert told Michigan Radio.

Lisa Williams, a contaminants specialist with the U.S. Fish and Wildlife Service, speculates that the fact that Caspian terns nest so close together could be the cause of the die-off.

“For a disease that’s transmitted through the air, they’re in close enough proximity that that can happen fairly readily on their colonies,” Williams told Michigan Radio.

The Caspain tern die-off caused by Avian flu will impact the species for generations. In addition to the deaths, future generations will be smaller because so many nests were left unprotected. (Courtesy Wisconsin DNR)

Why the virus is hitting this species harder than others is the real question. Several other close-nesting seabirds have seen die-offs, including ring-billed gulls and cormorants, but nothing near the rate of the Caspian tern.

The latest strain of highly pathogenic avian influenza (HPAI) has been circulating since late 2021. The U.S. Department of Agriculture says it has been confirmed in 42 states, killing more than 40 million domestic birds, mostly through depopulation efforts at poultry farms.

The HPAI die-off is the deadliest since 2015 when a strain claimed nearly 50 million birds.