UPDATE 8/01/2017: Park today announces that trails associated with the Precipice, Jordan Cliffs and Valley Cove will reopen on Thursday, Aug. 3, after five peregrine falcon chicks fledged this year — down from 11 in 2016. Trails were closed on March 17.

Five peregrine falcon checks have fledged at nests at two sites in Acadia National Park this year, but for unknown reasons a nest failed at a third site that has yielded chicks in recent years, a biologist at the park said Friday.

Bruce Connery, wildlife biologist at Acadia, said there was a pair of adult falcons at Jordan Cliffs and it is believed they started a nest but then one of the adults disappeared around the middle of June, and the nest failed. Connery said he does not know why the nest at the Jordan Cliffs failed but he said it was not related to the chicks or the nesting.

“My guess would be that one of the adults either left or was killed by a predator like a great horned owl,” Connery said.

On the positive side, the peregrine falcon chicks at the Precipice and Valley Cove have been flying since about July 1, and seemed alert and healthy when they were spotted by researchers, he said. At least one chick at each of the two sites was flying before the others, he said. “They are all flying now and they are doing great,” he said.

Three peregrine falcon chicks fledged at the Precipice and two at Valley Cove, he said.

The park usually waits for the peregrine falcon chicks to fly for five weeks before reopening trails, including the wildly popular Precipice Trail, that are closed in the early spring each year to protect the nesting falcons and chicks. The trails opened July 29 last year and usually open by early August each year.

Connery said the nest failure at the Jordan Cliffs was disappointing because the birds were there and everything seemed to be going along pretty well.

“It would be more understandable if we knew what caused it to fail,” he said, such as the male being attracted to another place.

“We just know we started seeing only one adult …. There was no real rhyme or reason to why it happened.”

Male and female adult peregrines both play vital roles in nesting. Females usually lay eggs in early spring and females incubate the eggs while males hunt and bring food to their mates, according to the web site of the Chesapeake Bay Field Office of the U.S. Fish and Wildlife Service.

Researchers at Acadia don’t know if it was the male or female adult peregrine that disappeared because the feathers of both sexes are mostly similar, but Connery said he would guess that it was the male that left or was killed.

Connery said he was pretty positive it was a “natural event” that caused the nest to fail. He said there is no evidence that human interference was a factor in the nest failure.

Fewer peregrine falcon chicks fly this year, compared with 2014-2016

The number of fledged peregrine falcon chicks at Acadia  this year was less than half the number that fledged last year.

Eleven peregrine falcon chicks fledged, or took their first flight, at the park’s three main nesting sites  – the Precipice, Jordan Cliffs and Valley Cove – on Mount Desert Island last year. Seven fledged at those three sites in each of 2014 and 2015.

Last year, the peregrine falcon nests at the Precipice on the east face of Champlain Mountain and Jordan Cliffs on the east face of Penobscot each produced four fledged falcons and the nest at Valley Cove, three.

In 2015, there were three fledged peregrine falcon chicks at the Precipice and two each at the Jordan Cliffs and Valley Cove sites.

In 2014, there were four at the Precipice, two at Valley Cove and one at Jordan Cliffs.

There were also two at Ironbound Island in 2014.

There have been no peregrine falcon chicks at Beech Cliffs above Echo Lake in several years. “That site has become less attractive,” Connery said. “I don’t know the reasons for that.”

The Precipice Trail, the Jordan Cliffs Trail, part of the Orange & Black Path and the Valley Cove Trail were closed March 22 to protect the nesting peregrine falcons. The tails should all open maybe around the same time as last year, Connery said. The trails usually do open by early August every year.

The park has not officially announced the date for reopening trails. Connery said he would work with Acadia National Park trails foreman Gary Stellpflug to have members of the park’s trail crew survey the trails along the cliffs and check some iron rungs on the trails, for example, before approving reopenings, he said.

There can probably be several hundred people a day on the Precipice in August, for example, so the park wants to make sure it is ready for a good amount of traffic, he said.

The five peregrine falcon chicks have all been banded with Maine’s black over green colors, he said, and the band numbers have been shared with Maine Department of Inland Fisheries & Wildlife. Banding does help track the birds during their winter migrations, he said.

Generally, peregrine falcons are believed to migrate south for the winter, but researchers are unsure of the life patterns of the peregrine falcons from Acadia, since funding does not allow for GPS  collars for tracking, Connery said. It is unclear if the Acadia falcons go only as far south as the Carolinas, or if they stay south for a month and then come back to the park around mid-February, when they usually stay to defend their territory, he said.

Peregrine falcons can fly 300 miles in a day, he said, so it can be easy for them to move north and south, depending on the weather and availability of prey such as pigeons and mourning doves.

Connery said he spotted a couple of adult falcons during the winter months in the park including one off Ocean Drive in early February of this year. There were other reports of the peregrines in Southwest Harbor and Valley Cove during the winter, he said.

Peregrine falcons were wiped out in nearly all of the eastern U.S. by the mid-1960s, because of the DDT pesticide.

Federal, state and private wildlife experts worked together to reintroduce the falcons and Acadia National Park was selected as one of the reintroduction sites in Maine, according to a press release by the park issued in March. A pair of peregrine falcons successfully nested in 1991 in the park and more than 125 chicks have fledged in the park since then, the  release said.

The peregrine falcon was listed as a federal endangered species in 1970, but was removed from that federal list in 1999.

The resident breeding population of peregrines remains endangered under Maine’s Endangered Species Act.

Peregrine falcons defend territory against Snowy Owl on Jersey shore

The Cornell Lab of Ornithology’s YouTube channel features this video showing the peregrine falcons’ territoriality, and features audio and life history of falcons on its Web site.