Blue herons find hiding spot in trees of Minnesota's Avon Hills

ALBANY, Minn. – A new great blue heron colony has settled in the Avon Hills, managing to conceal 6.5-foot wingspans amid a dense canopy of oaks.

Some bird-watchers have hoped for a revival or replacement of the long-abandoned Cold Spring rookery, which supported 1,585 great blue heron nests at its peak in 1974. They've wondered if great egrets, among the colonial water birds that shared that rookery on the Sauk River, might surface along a different stretch. The best chance of that discovery was during the five-year Minnesota Breeding Bird Atlas survey, which wrapped up in 2013.

Cliff Borgerding wasn't looking for herons or egrets. He came upon the colony quite by accident during one of his frequent walks in the Avon Hills Forest Scientific and Natural Area (SNA).

"All of a sudden I could hear this barking, almost like a dog," Borgerding said.

He looked down and saw a 3-foot-wide circle of whitewash. He looked up and counted 25 nests. This spring, he counted 45.

In early July, he revisited the spot with a reporter, a photographer and two cans of mosquito repellent.

We pulled off a back road halfway between Avon and Albany, walked west on the Wobegon Trail, and then entered the SNA. Vegetation obscured what was at best a faint trail into the woods. We waded through a tangle of stinging nettles, brambles and vines. We made inadvertent circles, recognizing the same fallen logs, climbing the same rises, skirting a swamp, kicking up clouds of relentless mosquitoes.

The birds vanished in 1989. No one knows why. The Minnesota Department of Natural Resources surmises a 1983 storm and 1988 drought might have contributed.

Partch died in 2003.

Colonies "grow and they shrink and then they desert altogether. I'm not sure that we know why that happens," said Mike Lee, a Sauk Rapids-based botanist and plant ecologist with the Minnesota Biological Survey who studied with Partch.

The sudden appearance of the Avon Hills colony illustrates the difficulty of tracking great blue heron population shifts. Counting is complicated by the fact that herons share rookeries with other colonial nesting water birds.

"We could count every colony in the state every year and [still not know] if a colony individually goes up or down," said Carrol Henderson, the DNR's nongame wildlife supervisor.

"It's kind of like squeezing a balloon. You squeeze one part, and they show up somewhere else," Henderson said.

In northern Minnesota, great blue herons often establish colonies in dead trees where beavers have dammed an area. The backed-up waters make good hunting habitat. Those types of colonies typically last 15 years, spreading outward as the trees in the center die — the so-called doughnut effect.

In southern Minnesota, great blue herons tend to establish colonies in living trees. Other colonial waterbird species move in. They're among the longest-lived rookeries, often persisting for decades.

The five-year Minnesota Breeding Bird Atlas survey turned up 34 records of great blue herons — the number of times the species was observed. It turned up one nesting record, on the southwest edge of Cold Spring. Statewide, the survey turned up 1,348 observations.

Borgerding, president of the Lake Wobegon Regional Trail Association, considered increasing trail-users' chances of seeing blue herons in the nest with interpretive signs. But the fact that this small colony is tucked away might allow the birds to flourish, biologists said.

People don't target great blue herons the same way they want to destroy other fish-eaters such as American white pelicans or double-crested cormorants — birds most often seen hunting in groups.

Nearly an hour into our heron-viewing excursion, we had only seen one nest (empty) and one gray feather. The air became more humid, which seemed to infuriate the mosquitoes. We stopped looking at mushrooms and started to focus on the keening of cars on Interstate 94 — our compass, should we decide to abandon the hunt.

Borgerding was first to hear the squawk. He was first to see the whitewashed leaves, to spot the stick nests high in the trees. We counted about 12 nests and a handful of well-hidden birds, their vessel-like silhouettes perched on slender branches, making such a ruckus it seemed impossible we hadn't noticed them before.

You want to see a great blue heron? Watch for them standing statue-still, stalking their prey in the shallows of lakes and swamps. They'll travel as far as 30 miles to find food.