Increase in heron nests seen at March Point

November 18, 2018

MARCH POINT — The 15.5 acres of protected great blue heron habitat on March Point is lush with ferns, moss and tall trees dotted with heron nests.

In recent years, the number of nests has increased throughout that area called the March Point Heronry.

The heronry is partially owned and partially held in conservation easements by the Skagit Land Trust. Land trust staff said they believe the increase in nests is due to herons moving into March Point as nesting habitat is lost in other areas.

An annual nest count the land trust has done at March Point since 2002 has documented as few as 258 nests and as many as 757 — the tally reached this year.

This year’s count was held Nov. 11.

Land trust Conservation Project Manager Jane Zillig said the number of nests has been increasing since at least 2014, when 486 were counted.

Throughout Skagit County, herons are often seen alone or in small groups on shorelines, in marshes and in trees. Zillig said the birds come together in large groups to settle in nests and raise young between February and August.

Land trust staff and volunteers enter the heronry during winter, when the birds are not using the nests, to count the number of nest and number of trees used for nesting.

Large trees in the heronry often hold many nests, becoming a sort of apartment complex for the birds, land trust conservation assistant Hannah Williams said while standing below a big-leaf maple with about two-dozen nests in it.

Williams and other land trust staff on Friday led a group of volunteers into the heronry to pull invasive plants such as European blackberry and English ivy and plant new trees.

“Hopefully those will become future heron habitat,” said Meagan Maillet of the land trust.

Williams and Zena Gavin, an AmeriCorps member working with the land trust, finished marking some of the trees where nests were found for the first time this year.

Land trust staff said they’re uncertain why the number of nests at the March Point Heronry appear to be increasing, but they believe it may indicate that herons that previously nested on Samish Island have moved in.

Skagit Land Trust Executive Director Molly Doran said herons disappeared from Samish Island in June 2017, a week after recently hatched young were observed. The herons didn’t return this year.

“One of the things we’ve been wanting to know was did they come here?” Doran said. “That increase ... could be that.”

Regional heron expert Ann Eissinger said she’s fairly certain the increase at March Point is related to the disappearance of herons from Samish Island.

“Those herons had to go somewhere,” Eissinger said. They didn’t just disappear ... they usually move elsewhere in the region and not too far.”

It remains uncertain why the herons so abruptly abandoned their nests on Samish Island. Doran said it’s unusual behavior because the birds will not abandon their young unless they feel seriously threatened, such as by a wildfire.

Those who monitor the Samish Island herons during the summer have suggested several possible triggers, including tanker traffic and fumes, smoke from fires or eagle predation.

According to the state Department of Fish & Wildlife, herons are known to relocate due to predation, human disturbances and food availability, and may return to a heronry up to 10 years later.

That means the land trust and volunteers have several more years to watch for whether herons return to Samish Island or the number of nests at March Point continues to grow.

Zillig and Doran said the March Point Heronry is already the largest nesting ground for the birds in Washington state and possibly on the West Coast.

Update hourly