For months, a male and female peregrine falcon, spied on from afar by local birdwatchers, have been hanging out on the Route 30 bridge near Columbia.

No one could see what they were up to because they disappeared under the bridge, but their actions were tantalizingly parent-like.

One falcon would alight on a pier, fly up into the span's undersides, and another would appear. Sure sounded like a nest exchange to Art McMorris, the Pennsylvania Game Commission's peregrine falcon coordinator.

Time to investigate and see if the pair indeed had established Lancaster County's first nest in at least 60 years.

So, on a recent steamy morning, McMorris, Dan Mummert, a Game Commission wildlife diversity biologist who lives in Lititz, myself and Meredith Lombard, a Columbia-area birder who first tied the falcons to the bridge, prepare to probe the noisy underbelly of the span.

In hard hats and climbing harnesses, we hoist an extension ladder supplied by PennDOT to the first bridge abutment on the York County side of the bridge near Wrightsville.

I am height-challenged, and only the thrill of the chase impels me to enter the narrow, see-through grate that serves as a catwalk under the eastbound lanes of the bridge across the Susquehanna.

Boy, is it noisy. Trucks thumping overhead sound like shotgun blasts underneath the decking and the bridge vibrates visibly.

I grip the two hand cables that parallel the catwalk and try not to look down. But, being a smallmouth fisher, I can't help scouting for fishy spots I'd like to wade out to later this summer.

Our anticipation is not just to locate a nest. We want to find a nest full of peregrine chicks. McMorris will capture and band the flightless birds so that they can be identified wherever else they might show up someday.

McMorris is carrying climbing rope and a fish net to catch chicks if he can't reach them. He's also got a cardboard dog-carrying box in which to temporarily catch and jail the adults if they aggressively defend their nest.

They sometimes do and McMorris has a talon hole in the back of his shirt from a banding operation on a bridge over the Delaware River just a couple days before to prove it.

He demonstrates how we should put our hands in front of our faces to absorb the talon-first blows of attacking parents.

Cool.

We have chosen the eastbound, downriver side of the bridge because the birds have been seen often on one of the piers about two-thirds of the way toward the York County side.

To our great disappointment, we find no falcon nest this day. The only evidence that peregrines were about is one dead blue jay and the leathered remains of a pigeon.

To add insult to injury, we have to duck under steel girders about every 15 feet on the catwalk. By the time we limp back to Wrightsville, our knees are buckling from the bends.

McMorris figures he and Mummert, who go the farthest, did 364 deep knee bends.

Mummert, who climbs into the uppermost reaches of silos and barns to band barn owls, declares it the most taxing field work he has ever done.

My thighs feel the burn for days. But when McMorris decides to check the upriver side of the bridge last week, everyone is game.

Once again we climb into the underbelly of the bridge. Topside, some 43,000 vehicles zoom across on an average day.

We navigate from pier to pier, scanning the beams. Near the same spot above the river as the week before, someone finds the carcass of a blue jay. Looking around, I spy in the shadows of an intersection of beams a round, brown object in a thin film of dirt.

"What's that brown thing over there?" I holler.

"That's a peregrine egg!" McMorris exclaims.

Indeed it is. But it's also cracked. While we're absorbing this bit of bittersweet news, Mummert, about 20 feet away, looks straight down through the catwalk and sees the remains of a dead mallard duck and a rabbit on a metal plate.

Next to them are two more eggs! Alas, they, too, are cracked.

McMorris surmises the pair of falcons nested once, then tried again when the egg failed. Since we have been up here three hours and not seen a falcon, McMorris concludes neither nest is active.

"They've abandoned them. They've left us alone. They don't care," says McMorris, having a ball in his second career as a falcon-nest explorer after 28 years as a research neuroscientist at the Wistar Institute in Philadelphia.

It's not unusual for nests to fail when young falcons make their first attempts. Perhaps the eggs were infertile. Perhaps the nest was left unattended too long and the eggs froze.

McMorris calls it a horrible nesting site and says flooding, wind exposure or even overheating also are possibilities for failure.

What's encouraging, though, is that the pair like this spot and will almost certainly try again here next spring. To improve their chances, McMorris plans on installing a simple nesting box, complete with gravel and a wing-exercising front porch.

Even if the eggs had hatched, the location of the two nests on narrow perches were precarious and it's likely chicks would have tumbled off or been blown off the bridge into the water 60 feet below.

Placing the box on the edge of a pier would give the falcons the sweeping, lofty view they favor for nesting.

We didn't get the instant gratification of downy-covered peregrine chicks. But as we make our long journey back to land, we are all buoyant in the knowledge that rare peregrines have come home to roost in Lancaster County.

We have found the 24th falcon nest in Pennsylvania, where the once endangered species is making a rousing comeback.

We expect to be making this same grueling but thrilling scouting expedition next spring — and look forward to witnessing McMorris get a new battle scar in his shirt.