An unidentified peregrine falcon might have replaced Erie, the male falcon that has occupied… An unidentified peregrine falcon might have replaced Erie, the male falcon that has occupied the nest on the 40th floor of the Cathedral of Learning since 2002.

Based on observations of behavior differences and photographs, falcon followers suggest that he is not Erie, the father of 22 chicks with the Cathedral’s female falcon, Dorothy.

Dorothy laid her eggs for this year around Easter. To avoid disturbing incubation, and also because the birds are highly aggressive toward any intruders at the nest, the Pennsylvania Game Commission cannot get to the nest until late May at the earliest, according to Tony Bledsoe, a biological sciences professor who helps monitor the falcons.

“If we can get a good, direct look at the male’s bands, we should be able to read them,” Bledsoe said, referring to the identification tags around the falcons’ legs. “We then can check against birds with known band combinations to determine his identity.”

Although Erie’s disappearance remains a mystery, observers suppose that the new male, Erie 2, or E2 as he has been dubbed, took over the nest without a coup.

“Turnover does not always involve fighting over the territory,” Bledsoe said. “Sometimes, males will disappear, presumably by death, and other falcons looking for territories will adopt the territory. That kind of turnover, if carefully monitored across time and many territories, can provide evidence about the size of the population looking for new territories.”

However, nests often change control when a young Peregrine falcon – male or female – defeats an older bird. Last year, Erie defeated a younger falcon that attempted to take over his nest.

“We found the defeated male’s carcass near the nest box when we removed it in preparation for the restoration of the exterior of the Cathedral of Learning,” Bledsoe said. “The defeated male had bands that let us identify him as Pulse, a bird bred in Cleveland.”

Only Dorothy was present during October of last year, as noted by ground observers. E2 arrived in the latter half of November.

“If Erie would have migrated, he would have been back this spring,” said Kate St. John, a National Aviary volunteer who monitors and maintains a blog about the Pitt falcons. “And he had never migrated before.”

St. John first suspected that Erie was missing. She noticed in February that E2’s ankle bands, used to track and identify the birds, were of different colors than those Erie wore. She spent six weeks comparing 4,500 photos of Erie and E2. She also noticed a difference in the color and pattern of the birds’ feathers, according to her blog.

Peregrine courtship involves a fancy type of flying including swooping and circles, which E2 and Dorothy demonstrated in November, at a time that would have been thought unusual for Erie, according to St. John. The courtship also raised suspicions of a new male falcon.

“E2 seems thrilled to be a father,” St. John said. “He incubates the eggs a lot more than Erie did, at least more than in Erie’s older years.”

For more information on the Cathedral falcons, visit St. John’s blog at www.wqed.org/birdblog.