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Pennsylvania's great blue heron on the rise

| Friday, July 10, 2009

Along the Red Belt in Franklin Park, where the road climbs along a high ridge, a large grove of massive sycamores rises over a hundred feet from the stream-fed valley below.

More than 40 huge nests adorn the wide crowns, and toward them, very large birds sail in on widespread wings, croaking to their mates below. Out of the piles of sticks raise the heads of hungry young. The returning birds, bringing food back from foraging, descend ever so slowly, their long, fragile legs dangling till they settle, parachute-like, on the nests.

If there is a single adjective to describe the great blue heron, it is majestic.

Four feet high, with a 6-foot wingspan, the largest of herons in North America strides, hunts and flies with a slow, expansive grace. At the top of the aquatic food chain, this highly visible wading bird is an excellent indicator of environmental health, and is used by state biologists to monitor the condition of Pennsylvania's waterways and wetlands.

More gray-blue than blue, this handsome bird sports rusty thighs, black wing feathers, a long, snake-like neck, white face and long, black plumes that sweep back behind its head. Its eyes glow deep gold, and in the breeding season its long, sharp bill turns from yellow to orange. Its flight is slow and deliberate, with full, powerful strokes, its neck tucked into a tight S, its long legs trailing behind.

Great blue herons are on the increase in Pennsylvania and, unknown to many residents, the Pittsburgh area is home to several breeding colonies -- called rookeries or, more specifically, heronries. A State Game Commission survey of wading birds in 2007 showed that heron nests increased by 32 percent since 2002.

In the Pittsburgh area, the rookery in Franklin Park increased from 21 to 41 nests, and three new colonies were established: 17 nests appeared on Twelvemile Island, another 9 at Boyce Mayview Park and 17 more in Deer Creek. Since the survey, a single nest has been built in Allegheny Cemetery.

Just how many rookeries exist in the area is hard to say according to Beth Fife, wildlife conservation officer for the State Game Commission.

"The exact number is difficult to assess because we are finding new ones all the time. Family groups expand to a point and then split off. They seem to sense the limit of the trees, and only establish densities of nests that won't take down the supporting branches." Fife adds that sycamores are a "highly important tree due to their wide, open crowns that allow for the building of nests and (accommodate) the 6-foot wing spans of birds that look like pterodactyls."

Family affair

Their platform nests of twigs and sticks can be 4 feet across, which they line with pine needles and moss. Because they generally return to the same rookery each year, they often reuse old nests, but do plenty of rebuilding.

In early spring, three to seven bluish-green eggs are laid; and 28 days later, by April or May, the chicks hatch. The young spend the next six to eight weeks growing rapidly, eventually walking around the nests, stretching their wings, and even taking short practice flights in the branches. This is an entertaining time to visit a rookery, when the young are getting ready to fly.

During the entire breeding season, males and females take turns incubating the eggs, guarding the nests and foraging for food. Each dawn, herons begin to leave the nests and visit ponds, streams, lakes and even cultivated fields to hunt. Their favorite food is fish, but they also take frogs, crayfish, rodents and snakes.

A heron on the hunt is a study in the art of patience. The bird strides very slowly; then for moments on end it remains motionless, allowing fish to gather around its feet, its long, pointed beak poised for the strike.

Its stalking involves all the art of the spear fisherman, including the intensity of focus, trained eyesight and lightning-quick response. The only difference is that the beak, stabbing suddenly toward its prey, opens at the last moment and acts as a deft pair of forceps. The fish, crayfish, or frog is turned in the beak and swallowed headfirst.

Once its stomach is full, the bird lifts off from the water with its wide wings and makes the trip back to the heronry to regurgitate its catch to its mate and young.

Between July and August, the full-grown young fledge, and both young and adults revert to a solitary lifestyle, foraging along waterways until October when most migrate south. They fly day and night until they reach more southern states, and some fly as far as the West Indies and Central America. A few hardy individuals stick around Pennsylvania, finding food along unfrozen rivers and ponds.

"A lot of ours stick around," says Beth Fife. "Our milder winters give them the opportunity to hunt in waters that stay open and that is all they need."

The urban buffet

Jim Bonner, executive director of the Audubon Society of Western Pennsylvania, says this is when they receive quite a few calls about great blue herons, the a‚ÄĘcallers often wanting to identify the birds, which many people mistake for storks or cranes.

"But this is also a time when the herons find easy hunting in backyard ponds," he says, "and we receive quite a few complaints about the birds eating people's prized koi."

Almost every winter, a heron or two takes up residence at the Pittsburgh Zoo where they not only find goldfish in some of the artificial waterways, but also will beg for fish from keepers feeding sea lions or other animals.

The great blue is one of the largest members of the heron family, a group of 60 species of wading birds that range almost the entire world. Seven other members breed in Pennsylvania, including the green-backed heron, great white egret, black-crowned night heron, yellow-crowned night heron, least bittern and American bittern.

Great blue herons return to Pennsylvania in late February or early March. Each year, they choose a new mate with elaborate courtship displays in which they exchange branches, clack their beaks, erect their head plumes and dance excitedly with raised wings in preparation for the new breeding season.

Although each pair of herons might successfully produce two to four fledglings per season, mortality rate is quite high, perhaps 70 percent or more. Raccoons are their greatest enemy -- quite willing to clamber up the tall trunks and rob nests of eggs and chicks. Crows, ravens and hawks also take their toll. However, those birds that do reach adulthood can live for 15 years or more. One Florida heron lived for more than 23 years.

Despite various threats, Pennsylvania's great blue heron population continues to grow. The Barrows heronry along the Little Shenango River in Mercer County is the largest colony in the state with more than 400 nests in some years. Many of the Pittsburgh-area rookeries have been in existence for more then 15 years.

"We've been seeing herons everywhere we go," says Beth Fife. "The expanding population is really due to better water quality, more abundance of wetlands, everything."

Indeed, the fact that these birds have expanded in density and number in recent years is testimony to the lowering of pollution in rivers, streams, ponds and lakes.

Although the great blue heron is still a fairly common species, their rookeries are susceptible to destruction by the draining and cutting of forested wetlands where they most often make their colonies. Human disturbance can also cause herons to abandon a rookery; so interested observers should remain as unobtrusive as possible.

Mark Browning is a zoologist for the Pittsburgh Zoo & PPG Aquarium and a nature writer.

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