Feed me, feed me, now Jamie Felton/Getty

Short rations for America’s iconic raptors. A team at Florida Atlantic University installed cameras at four bald eagle nests in Florida Bay, between the southern mainland and the Florida Keys, to figure out why the population has been declining.

They found that eagle parents were feeding their young less than twice a day – nearly half what eagle chicks get to eat in other regions. The team also observed that the biomass of the food deliveries declined throughout the breeding season even as the chicks grew larger, suggesting that the parents weren’t finding enough food.

Eagles in southern Florida have symbolic value. “Florida has always historically been a stronghold for the species,” says Bryan Watts at the College of William and Mary in Williamsburg, Virginia.


It’s the southernmost extent of the species range. While bald eagle numbers crashed throughout the continent in the 1970s as eggshells were thinned by DDT, the Florida Bay population, largely free of pesticides, held steady, he says.

Killer salt

The study concluded that a collapsing Florida Bay ecosystem isn’t supporting the eagles any more. In recent decades, high salt concentrations have killed off sea grasses, releasing sediments that triggered algal blooms.

The knock-on effect has killed many fish that eagles depend on for food. It’s possible developments in the Everglades have disrupted the flow of fresh water into the bay, setting off these problems.

Ospreys, another raptor species that relies even more on fish, have also dwindled in Florida Bay, says Watts.

“The same fingers are pointing to food stress related to an ecosystem-wide change,” he says. “One of the benefits of monitoring ospreys and eagles is that they’re an indicator of what’s happening underneath the surface.”

However, bald eagles aren’t in trouble in most of the US, says Watts. After recovering from the 1970s decline, the species has thrived. “Their numbers are huge across the continent now,” he says.

Journal reference: Southeastern Naturalist, DOI: 10.1656/058.015.0218

Read more: United States of extinction: Threat to America’s iconic animals