A Rookery Rebounds
by Gail Goldberger

he great blue herons started landing in late February, swooping into the highest levels of the almost completed rookery. As pairs passed twigs back and forth in an elaborate mating ritual, workers feverishly erected the final structures designed for this year’s throng of migrating wading birds. Throughout February and early March, they labored in shifts, men by day, birds by twilight.

Telephone poles, Christmas trees, and 1,300 birds at Baker's Lake Nature Preserve. Photo by Robert Sliwinski.

On a raw, cold March morning, volunteers lined up to help staff from the Forest Preserve District of Cook County finish construction. Armed with evergreens and logs for ground cover, and bracket mountings for carved-out Christmas trees, they completed the project. And what a project it is!

Stop at the gravel driveway on the north end of Baker’s Lake in northwest Cook County and you will see an incongruous configuration rising out of the lake, a towering manmade aerie of nests, poles, beams, wings, beaks, and fuzzy heads. You will be looking at perhaps the most comprehensive heronry reconstruction ever.

The restored rookery holds 315 nesting pairs of birds, up from 200 last year, including eight black-crowned night heron pairs. With an average of two juveniles per nest (one for the night herons), there are a total of 1,300 birds on the island. By anyone’s count, a success story.

More than 20 years of care have been poured into Baker’s Lake Nature Preserve, and the list of those responsible is as jam-packed as the rookery. Success is a testament to what happens when natural resource agencies and concerned and supportive citizens work together for wildlife.

The story began in the early 70s, when the Forest Preserve District of Cook County bought the lake, island, and buffer zone. Staff of the Illinois Department of Natural Resources and Illinois Endangered Species Protection Board conducted first surveys in 1978-79. Max McGraw Wildlife Foundation staff secured grants from Illinois Endangered Species Protection Board in early 1980s to conduct more extensive surveys. In 1984, the lake and surrounding area were dedicated as a state nature preserve because the heron colony supported a nesting population of the state endangered black-crowned night heron.

The first artificial nesting structures on the island were designed by Max McGraw staff and were erected with the help of staff of the Forest Preserve District in March 1986. From 1986-1990, the black-crowned night herons occupied the highest, best nests, and their numbers routinely exceeded 200 pairs.

Other larger birds — great egrets, great blue herons, double crested cormorants — discovered the island and took over the higher spots, forcing the smaller heron to lower, less desirable nests. Nest count for the smaller black-crowns plummeted from 220 to 11. Last year, counters weren’t sure there was even one black-crowned nest left on the island.

Over time, the acidity of fecal droppings on rookeries depletes vegetation. Put bluntly, bird poop kills the trees the birds require for their nests. Where suitable, isolated nesting locations exist, birds move to new areas to nest and breed, often returning to the original rookery once it has restored itself. Not surprisingly, these birds are sensitive to human disturbance and typically colonize isolated locations (such as islands) that are also secure from predation. In the Barrington area, however, despite plentiful marshes for feeding, the only protected spot the herons had for nesting is this one little island, 150 feet long and 50 feet wide.

The first artificial structures proved successful, and the birds readily used them. Year after year, blue herons, egrets, night herons, and cormorants left the Gulf of Mexico and Florida, and returned to Baker’s Lake. Their attachment to this island is profound and demonstrates their resiliency to changing conditions. The attachment goes both ways— Barrington residents and area naturalists also love and value these birds.

In recent years, as the island eroded to a sliver and the last tree blew over, a local conservation group — Citizens for Conservation (CFC) — played an important role, advocating for nesting structures. The prime mover and shaker, Patsy Mortimer, helped gather the relevant parties and kept them focused on the birds.

"There has rarely been an engineered solution to a habitat problem as extensive as this one," says Dave Kircher of the Cook County Forest Preserve District. He ought to know. The District paid $250,000 to restore the rookery. They hired Christopher B. Burke Engineering to design a nesting structure and Landscape Resources to install the structures.

"We looked at what worked in the past," said Robert Sliwinski, Senior Environmental Resource Specialist at Burke Engineering and project manager for the heronry reconstruction. "A lot of science went into this." They designed 25-foot tall nesting structures with longer, more angular arms — "watchtowers" — to more closely resemble the crooks of trees. They put a 10-foot fly zone between nests for the great blue’s wing span, and widened their nests to five feet. They shortened the arms on lower-level structures for smaller birds. The final blueprint contained four levels of nests, with enough space in between to reduce the stress of congestion. Evergreens with carved-out nest bases were mounted on poles, as well as stockpiled on the ground to provide shelter for black-crowned night herons.

Six different structures comprised the new rookery: two modified from those used by Will County FPD’s Lake Renwick heronry and four used by Wisconsin’s Department of Natural Resources. Pole mounts were set in cement for stability. Commonwealth Edison donated the 40 paired telephone poles, and Barrington’s Citizens for Conservation donated 300 Christmas trees and the lumber and labor for nest structure building. "I held my breath until they started to land," said Sliwinski.

"From the District’s standpoint, we poured a lot of money into something untried. We hoped we wouldn’t see a drop in numbers," said Kircher. "We weren’t even sure the birds would recognize the island, and thought the construction workers would scare them away."

Apprehensions notwithstanding, the birds returned, accommodated the workers, and survived a strenuous spring that included baseball-sized hail and 60 m.p.h. windstorms. (The great blues stretched out flat across the tops of their nests.)

With 1,300 birds and babies, life is zestful here. The noisy compacted throng attracts many onlookers, who themselves swarm to gaze at the crosshatching that supports 315 nesting pairs. Birders have been overheard saying, "We feel so fortunate to have something like this right here!"

Even this extensively researched project is a work in progress. Birds didn’t go where anticipated. Egrets preferred lower-level structures and carved-out evergreens. Cormorants nested anywhere they could, cramming the crossbraces and junctures with twigs and grasses.

Black-crowned’s went to the brush cover. Robert Sliwinski confirms eight nests with eight nesting pairs. Two sets of nests had three juveniles, and two more juveniles were sighted. He thinks there are probably more black-crown nesting sites that he couldn’t see, buried inside the brush cover.

"Next year," said Steve Byers of the Illinois Nature Preserves Commission, "we’ll pack in more evergreens to attract more black-crowneds. They prefer nesting in tight places that provide some protection from their larger neighbors. The Christmas trees provide that cover."

In late June, at the height of breeding season, CFC’s Patsy Mortimer organized a celebration for all involved in this unusual project. As the western horizon turned a dusty orange, a tree on the east bank of the lake began to fill with black-crowned night herons. When the sun disappeared, they flew out across the lake to fish. As partygoers looked out from a deck with a view, the night herons flew overhead, sealing the night with a benediction of sorts, the bond between avians and humans secured.