F. Arthus McMorris, the peregrine-falcon coordinator for the Pennsylvania Game Commission, said he spent Monday banding the birds, which are the offspring of a mated pair among just 33 known peregrine falcons in the state, the Philadelphia Daily News reported Tuesday.
McMorris said there were originally five babies, but one of the birds died shortly after hatching.
The official said the parents have been attacking people who come too close to the nest, showing they are doing well by their offspring.
"The more aggressive they are, the more we like it," McMorris said. "That means they're better parents."