The region's population of peregrine falcons is not yet soaring, but the numbers are flying in the right direction.

National Aviary and Pennsylvania Game Commission officials said they've identified four nests in the Pittsburgh region -- and there could be more.

In recent weeks, officials banded two peregrine chicks atop the Gulf Tower, Downtown, three atop the Cathedral of Learning in Oakland and four chicks in a nest on the Monaca-Rochester Bridge spanning the Ohio River in Beaver County.

They also have discovered two eggs in a nest on the McKees Rocks Bridge, which spans the Ohio River in Allegheny County.

Although peregrine eggs typically hatch earlier in the spring, Todd Katzner, aviary director of conservation and field research, said the unhatched eggs might be the spawn of a pair of young falcons, who sometimes breed later in the season. Another possibility is that an interloper took over the nest, and the disruption pushed back the breeding season.

If the eggs do hatch, this year's total will climb to 11 chicks.

"We've got nine guaranteed chicks," Dr. Katzner said. "Last year we had 10 in the area."

The chick count is steady, but the four active nests indicate the local population is rising, Dr. Katzner said.

"With a species like peregrines, there never will be a super high density, like robins or sparrows," he said. "Because of their natural low density, they always will be at a somewhat higher risk. But the population is increasing and that's a positive sign."

Since 1991, 61 healthy chicks have hatched atop the Gulf Tower. Another 25 have hatched atop the Cathedral of Learning since 2001, with six hatching on the Monaca-Rochester Bridge. While the McKees Rocks Bridge has yet to produce any chicks, that could change in coming weeks.

Peregrines became endangered nationwide due to the deadly impact of DDT contamination. After the pesticide was banned in 1973, the population began a comeback.

No longer endangered nationwide, the peregrine remains endangered in Pennsylvania, where only 24 pairs have been counted.

Peregrines, which prey on other birds, are the world's fastest animals. They can make aerial dives during mating rituals that can approach 200 mph. Efficient predators, peregrines dive 60 to 100 mph to attack and kill birds in flight.

Key to re-establishing a stable peregrine population is getting them to return to natural nesting sites, which has begun to occur.

The game commission has confirmed that a pair of falcons has established a natural nest on a cliff in Union County near Northumberland. It's only the third wild nest that peregrines have established in Pennsylvania in a half-century. In 2003, a pair nested on a cliff in Lycoming County, which signaled that peregrines were returning to the 40 cliffs statewide where the falcons had nested prior to DDT contamination.

Once the number of pairs nesting in natural settings exceeds 20, the peregrine will be removed from the state endangered species list, the commission said. Twenty-one pairs currently nest atop buildings and bridges in Pittsburgh, Philadelphia and Harrisburg.

Peregrines also face natural obstacles. Great horned owls prey on young falcons, blocking their attempts to resettle in Pennsylvania's wilds. By first re-establishing a population in cities, the state has foiled the owl and generated enough peregrines to survive predation.

But the commission said speedy peregrines face other challenges in urban settings, including windows and traffic. But the regal bird's outlook for survival is cautiously optimistic.

"Because they are increasing, it doesn't give license to stop protecting them or to do things to inhibit their ability to remain stable," Dr. Katzner said.