PROSPECT – In its own version of “Guess Who’s Coming to Dinner?” the Maine Department of Transportation is making plans to play host to two birds.

In preparation for the expected return of a breeding pair of peregrine falcons that last year established a nest under the deck of the Waldo-Hancock Bridge, the department – working with the state’s Department of Inland Fisheries and Wildlife – has set up a nest box on the bridge’s western tower below the travel way.

Last year, the pair laid eggs on a steel beam under the bridge deck. But, although initially the pair seemed to disregard repair work on the bridge, the eggs did not hatch.

“Probably, because of all the activity, and the eggs were left too long, they got cold and died,” DOT Supervisor of Field Studies Richard Bostwick said Tuesday.

Peregrine falcons are small raptors, about the size of a crow, that catch their prey in flight, often swooping down on other birds from above, and are likely attracted to the bridge by the ready supply of pigeons that also roost there. They’re considered the fastest birds alive: in a dive, they can reach speeds of more than 100 mph.

The falcons – which are no longer on the federal endangered species list, but remain on Maine’s endangered species list – are known as “scratch birds” because they lay their eggs in debris usually found in their natural nesting areas on the side of cliffs.

There were 16 pairs of nesting peregrine falcons in Maine in 2003, the result of a restoration effort that began in 1984.

A pair of peregrine falcons had been seen in the area in recent years, and some speculated that they may be offspring of pairs of peregrines that have successfully nested in Acadia National Park during the past decade. According to Bostwick, however, last year was the first year there was evidence that this pair had nested.

This year, the department wanted to be prepared for the birds, so, using plans obtained from a utility company in Minnesota, a crew built a cedar nesting box with a gravel bed and installed it on the tower.

“The box has a roof on it and a front porch and a perching pole,” Bostwick said. “They like being in it and surrounded by things.”

The perching pole gives the birds an opportunity to check out their surroundings before taking off from the nest.

The nesting box, however, is only temporary housing, and the department hopes eventually to move the birds off the old bridge long before it is dismantled.

“The benefit of providing a nest box is twofold,” Bostwick said. “First, it would provide more shelter for the birds’ eggs, making it more likely that we’ll see a successful hatch.

“Second, once the bird has become acclimatized to this nest – say two years in a row – we could move the box to a more permanent location on the new ledge face on the westerly approach.”

The department is in the process of building a new $75 million bridge across the Penobscot River to replace the 72-year-old Waldo-Hancock Bridge, which has deteriorated to the point where it is not feasible to repair it.

Crews will begin blasting the ledge along Route 1 in Prospect to create a new approach to the new bridge.

The old bridge has been a popular site for birds. Two pairs of osprey had been nesting atop the bridge towers for about five years, and it took several attempts and a chicken wire tent to get the osprey to relocate.

One pair apparently headed into the wild, but the other moved into an artificial nest set atop a 40-foot pole in the former campground site adjacent to the bridge.

The campground is now the staging ground for construction of the new bridge, but state wildlife biologists do not believe the activity will disrupt the osprey nesting site or their breeding. Neither the falcons nor the osprey have been spotted in the area this spring.