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Abandoned Nests: Why Are Great Blue Herons Disappearing from the Northern Metro?

by Jennifer Amie

Each year around St. Patrick's Day, the great blue herons return to the Rice Creek chain of lakes, where they have nested since 1945. Their rookery on Lake Peltier island, on the border between Lino Lakes and Centerville in Anoka County, is home to some 200 of the large, majestic birds.

The island's maple basswood forest provides the tall trees necessary to support the herons' nests, built from shaggy snarls of twigs and nestled in branches as high as 60 feet off the ground.

In spring, the herons work to repair their nests, flying across the lake to gather sticks from nearby fields. In late March or early April, the female birds begin to lay their eggs, which they will tend over the following months. Typically, the herons remain in or around the colony throughout the summer as they raise their young. In mid-September or early October, they begin their southward migration.

In March 2000, retired U.S. Fish and Wildlife Service biologist Art Hawkins was preparing for his second season observing the Lake Peltier herons on behalf of the Minnesota Department of Natural Resources (DNR). He set up his spotting scope in a farmer's field across from the lake, watching the birds fly back and forth across the water to fetch twigs and hunt for food. By May, the colony was well- established in what appeared to be a typical nesting season. Then suddenly, in early June, the rookery went silent.

What would cause an entire colony of birds to abandon their eggs and hatchlings? "Whatever it was, it was a massive disturbance," says Hawkins. "Birds are notoriously faithful to their nests during the late stages of incubation or with young to feed, conditions that prevailed when the mass desertion took place."

Although such a mass abandonment during the height of nesting season is unprecedented, the summer of 2000 was not the first time the heron colony had been displaced from the Rice Creek chain of lakes-and it would not be the last. As many as 400 herons returned to nest at Lake Peltier in the spring of 2001-but in June they once again abandoned the rookery.

"A bird catastrophe of this magnitude is hard to assess," says Hawkins. Many unanswered questions remain. For two seasons now, the colony has produced no surviving young, and no one knows what the ultimate effect of these losses might be. Nor does anyone know where the herons went after they left the rookery, or whether they might one day decide to abandon Lake Peltier for good.

In many ways, the forested island on Lake Peltier may represent a last stand for the herons that have endured both natural disasters and human expansion into their habitat.

Great blue herons first began to inhabit Lake Peltier in small numbers in 1989. Today's colony, which has declined in population to about 200 birds, is believed to have assembled from the remnants of two earlier colonies that were displaced from nearby lakes.

Beginning in 1945, a colony of hundreds of herons nested on Rice Lake, south of Lake Peltier. These birds were displaced in the early 1990s by residential development and the opening of a nearby golf course, according to Joan Galli, a nongame wildlife specialist with the Minnesota DNR.

A second heron colony inhabited Howard Lake, north of Lake Peltier, and once numbered 550 nests. The Howard Lake colony suffered severe losses during a wind storm in 1987 that downed nest trees and killed many young birds. The colony never recovered from the storm's devastation and relocated to Lake Peltier.

"The herons have retreated-literally and figuratively-to islands of habitat that are remote from human disturbance," says Galli. "They're very precariously situated. There isn't any lakeshore they can go to, because it's all developed. Their options are more and more limited as we expand our residential occupancy of this world."

Today, the Lake Peltier heron rookery is one of only nine in the seven-county metropolitan area and is the second largest. Its birds fly up to 20 miles away to feed in ponds and marshes and along lake shores. "All the herons and egrets that citizens see in their backyards in Anoka and Washington counties are most likely nesting in this one colony," notes Galli.

In other words, the area's herons have all their eggs in one basket: Lake Peltier island, a 30-acre oasis in a community that is rapidly shifting from agriculture to suburban housing development.

Owned by Anoka County Parks, the island preserve is home to much more than the heron rookery. Forested with ash, basswood, elm, maple, and hickory, it provides habitat for deer and foxes as well as numerous birds-great egrets, wood thrush and veery, red-eyed and yellow-throated vireos, and scarlet tanagers, to name a few. The shoreline and shallows north of the island serve as a spawning area for Northern pike and walleye and as a resting area for terns, black crown night herons, and other waterfowl. The north arm of the lake, says Galli, is one of the few remaining places in the metro area with healthy native vegetation, including water willow, which is considered a species of special concern.

Ringed by swiftly growing suburbs, the once-secluded lake now faces increasing pressures from nearby residential development and recreational use.

"This is an area with lots of lakes, wetlands, and wildlife," says Marty Asleson, environmental coordinator for the city of Lino Lakes. "Folks who are moving in want to preserve it, and that's tough to do. Sustainability requires a balance between cultural and environmental issues."

The heron colony is widely considered one of the county's most outstanding natural features. In fact, the city of Lino Lakes adopted the great blue heron as its logo and even named an elementary school after the birds.

Since the colony's abandonment last summer, local residents, city and county officials, and wildlife experts have worked diligently to solve the mystery of the birds' disappearance.

With the help of Bell Museum director Scott Lanyon, an ornithologist and resident of Lino Lakes, 10 potential causes of the birds' abandonment were identified in January 2002. Upon further examination, nine of these factors were ruled out, leading a local task force to focus on the most likely possibility: disturbance caused by human activity near the rookery.

A heated debate emerged over the potential impact of a slalom waterski course that had been installed by local residents in the shallow waters along the north side of the island.

Though no one can prove that waterskiing is the direct cause of the colony's abandonment, many believe that the extreme disruption and repetitive nature of slalom waterski racing could have been sufficient to drive the birds from their nests.

"We received many comments from residents about high speed boat traffic so that was one of our primary considerations," says Perry.

Great blue herons are wary, skittish birds. Studies show that, like many birds that nest in colonies, they are particularly vulnerable to human disturbance and recommend a protected "buffer zone" of 250- 500 meters around nesting areas. Though enacting changes meant a complex collaboration across two jurisdictions, the city councils of Lino Lakes and Centerville moved quickly to protect the birds. The councils voted to relocate waterskiers to the southern portion of the lake. To protect the rookery and the sensitive ecological zone on the north end of the lake, they passed joint ordinances creating a no-wake zone starting approximately 250 feet south of the island. The north end remains open to fishing, canoeing, and slow-speed boating.

It is hoped that this new buffer zone will protect the rookery from disruption and allow the herons to complete their nesting season. The new ordinances will take effect this summer and will remain in place through 2004.

Although some residents opposed the no-wake zone, Galli says it was a necessary measure. "We don't think we can wait any longer," she says. "We need to take action now if there's anything we can do that might have meaningful consequences."

In addition, DNR and park staff members are working to minimize other traffic in and around Lake Peltier, including sea planes, mosquito control helicopters, and firefighting planes that collect water from the lake.

The successful coordination among the several jurisdictions responsible for Lake Peltier-and the swift action of two neighboring city councils-may serve as a model for the many other suburbs attempting to conserve natural areas in the face of increasing human activity.

As more and more people want to live closer to nature, many communities are forced to address the impact of increased residential development on their lakes, wetlands, and woodlands. The conflict between boats and birds in Lake Peltier is a classic example of a cultural and environmental clash, says Marty Asleson, who believes that the new ordinances will be an effective compromise.

In March of this year, Art Hawkins returned for a third season to the shores of Lake Peltier, toting a spotting scope and notebook and hoping to see the first arrivals in the herons' spring migration. As cormorants stood guard on the bog poles nearby, Hawkins has watched as great blue herons have once again flown back and forth across the water, fetching sticks for the nests they have abandoned for the previous two years. Now it is the beginning of May and so far, says Hawkins, everything seems to be going well.

To find out whether the new ordinances succeed in helping the Lake Peltier herons complete their nesting season, look for an update in the fall issue of IMPRINT.