Virginia Osprey Babies Dying of Hunger

Bay Journal, Researchers peg Mobjack Bay osprey woes on food shortage, caused by industrial scale Menhaden fishing

In “the good days” a few years ago, each of the 83 active osprey nests monitored in Mobjack Bay might have had one hatched egg by late spring, said Michael Academia, a researcher with the Center for Conservation Biology at the College of William & Mary in Virginia.

But recently, the nests have produced a total of just 10–15 hatchlings per year. And, during a check this June, there appeared to be only three young ospreys in all of the nests combined.

“Something’s not adding up,” he said.

In a paper published in the Frontiers of Marine Science in April, Academia contends that the cause of these dips in nest numbers is a shortage of food — namely, Atlantic menhaden. The center has been tracking the health of local osprey populations since the 1970s and sees “an inextricable link” between the birds and the nutrient-rich fish that travel in schools near the water’s surface in the ocean and estuaries.

A study in the mid-1980s first identified that menhaden often make up nearly 75% of an osprey’s diet. A 2009 study showed that is still the case the closer the ospreys are to the mouth of the Chesapeake, while upper Bay birds tend to have a more varied diet. Mobjack Bay is located directly off the lower Chesapeake, near the area where Chesapeake menhaden harvesting is most active.

Besides feeding predators like osprey, menhaden are the focus of one of the largest commercial fisheries on the Atlantic Coast. The health of that fishery is measured and managed as a coastwide population, making it difficult to determine how local or Chesapeake populations of the fish may be faring.

The Bay is also home to the world’s largest breeding population of ospreys. Many of them migrate into the area in early March to breed before heading south in mid-August for the winter.

For Academia, who grew up as the son of a commercial fisherman in Hawaii, ospreys “are the proverbial canary in the coal mine” for menhaden abundance. “We were taught before technology to look at birds to locate fish,” he said. “If the birds are doing OK, then there’s a lot of fish.”

There are exceptions

Because he lacked abundance data for menhaden in Mobjack Bay, Academia and Bryan Watts, director of the center, conducted an experiment in 2021 and published the results this year.

They divided breeding pairs of ospreys into two groups, supplementing the diets of one group with additional menhaden to see whether there was a relationship between more food and more hatchlings surviving. A nest was considered a success if it had one survivor (female osprey typically lay three eggs in late spring).

Among the nests that received food supplementation, 81% succeeded, compared with 33% in the control group. The supplemented nests had an average productivity rate of 1.13 young per active nest, close to the 1.15 rate that’s needed to offset mortality in the osprey population and make it self-sustaining.

"It's Snakehead or nothing!

The control group’s fertility rate of .47 young per active nest was lower than the fertility rate for ospreys in the 1960s, when the widespread use of the pesticide DDT pushed populations of ospreys, eagles and other birds to the brink. A 1972 ban on DDT helped Chesapeake ospreys recover from an estimated low of 1,450 breeding pairs. The breeding pairs recovered to about 3,500 by the mid-1990s. Watts has estimated that as many as 12,000 pairs today consider the Chesapeake region home.