Is that the call of a mourning dove or a house finch? A sharp-shinned hawk or a golden-winged warbler?

The average person may not be able to tell which bird is which by its song, but then again George Casselberry is not your average person when it comes to birds.

A 22-year-old docent at the National Aviary on the North Side, Mr. Casselberry, who is visually impaired and has cerebral palsy, can identify birds by their sounds. He's so gifted in this area that he has even helped aviary staff identify birds.

Mr. Casselberry is one of the 5.1 million Americans who have some level of disability and one of several working as volunteers at the aviary. Today is the 18th anniversary of the Americans with Disabilities Act, which is aimed at guaranteeing equal opportunity in public accommodations, commercial facilities, employment, transportation, state and local government services and telecommunications.

Many times people with disabilities bring special gifts and talents to the workplace and other venues.

Mr. Casselberry "has seen with his ears birds that I have not seen yet in the park visually," said Steve Sarro, director of animal programs at the aviary, who conducts nature walks for visitors with Mr. Casselberry. "There are birds in the park such as warbling vireo and cedar waxwing that I have not seen but just about every day he hears them, and I trust that he knows what he's listening to."

Mr. Sarro said the New Castle resident also is well-versed in bird natural history and can talk in detail to visitors about the birds he's identifying.

As Mr. Casselberry sat in his wheelchair in the aviary's tropical forest earlier this week, he called out the names of the birds singing overhead as he explained how he developed this talent.

"I've been interested in birds since I was 4 years old," he said as he pointed out by its call that a black parrot was flying over. "I remember back then when my parents took me down here [the aviary] for the first time. I was just in awe, if you will, of all the different birds. That's what sparked my interest."

His parents bought him an audiotape of the 53 most common backyard species of birds.

"I've just been learning bird calls ever since," he said.

Mr. Casselberry, who graduated in May from Slippery Rock University with a degree in early learning and childhood development, gets the chance to share his love of birds and their songs with the parents and youngsters who visit the aviary and take the daily wildlife walks through West Park.

His work as a docent is fulfilling his academic internship requirements. While at the aviary, he is accompanied by an aide who drives him to the aviary and assists him throughout the day. When the aide is off, his mother, Bonnie, fills in.

Initially, because of his degree in early education, Mr. Casselberry expressed interest in the aviary's education internship. But that required a person who could transport children to different facilities, he said.

"So I called them to see if I could do my internship as a docent," he continued. "They interviewed me and they knew about my talents and they really wanted me to do the nature walks as well as other projects."

In addition to his docent duties, Mr. Casselberry has also been asked to assist with a project to identify species and collect data on birds on Mount Washington and also a bird-banding program at Powdermill Nature Reserve in Ligonier Valley.

He said a lot of people who attend the aviary's nature walks think all there are to see are sparrows and pigeons, "but we've had a lot more species than that."

A couple of days ago, Mr. Casselberry was able to identify the sound of a lyric cicada.

"My natural sound expertise is not limited to birds," he said. "I can do frogs, insects, what have you."