Ways of the Wild
5:01 am
Mon May 13, 2013

Eagles return, drive entire colony of herons out of Kiwanis Ravine

The great blue heron is one of Washington’s most iconic birds, as is the bald eagle. Now, it seems eagle attacks on heron nests are driving herons to abandon the largest colony in Seattle. And volunteers are asking local residents to help them figure out where the herons have gone.

For more than a decade, Pam Cahn has monitored the dozens of heron nests at Kiwanis Ravine near Discovery Park in northwest Seattle. The volunteer citizen-scientist has kept track of eggs laid, chicks hatched and fledglings flown, then sent the data to the state Department of Fish and Wildlife for record-keeping.

But Cahn says this season, eagles have wreaked havoc on the approximately 90 heron nests in Kiwanis Ravine.

“It’s a continuing problem, but this year, the results are more devastating,” she said.

The harassment peaked last week when the entire colony abandoned their homes, leaving behind eggs, chicks, and a live heroncam showing nothing but an empty nest.

“This past week, all of the nests were abandoned by the adult herons, and all the remaining eggs—and there were some young chicks on some of the nests—were destroyed or eaten,” she said.

Cahn says many of the herons seem to have relocated to a nearly area in Commodore Park where the number of nests has grown from six to 40 in barely a week. But many others are still unaccounted for, Cahn said, and Commodore is not without its own predators. 

“There are now clear indications that the eagles are causing problems there already,” she said. “Indications of several dropped chicks.”

Biologist Chris Anderson with the Department of Fish and Wildlife says until recent decades, this kind of pressure from predators was pretty normal for herons.

“Eagles and other raptor species, birds of prey, their populations were depressed for a while, you know, 30-40 years back. And now many of those species are recovered or are recovering,” he said.

And that means the normal push and pull between eagles and herons is reappearing. If anything, Anderson says, the challenge to both species is loss of habitat to human development.

Now, the trick is to locate the missing herons.

“They may disperse for the season and not try again. They may go to other colonies farther away, which is why I’m interested in people keeping an eye out for new nest-building activity,” said Cahn. “Or they may go into stealth-mode and have nests here and there. Sometimes they’ll go into conifers, (nests in) which are really hard to spot (for predators).”

The nonprofit group Heron Habitat Helpers is asking Seattle residents to keep an eye out for new heron nests or signs of nest-building, such as herons carrying twigs in their bill. Any information about the new whereabouts of the Kiwanis Ravine refugees will help wildlife managers keep up-to-date on these majestic birds.