The students at the Pennsylvania School for the Deaf had set up the bait:  a buffet of bird seed and peanut butter served on tree stumps,  pine cones, and empty egg cartons.

Then they waited.

Some peered through windows. Others walked the campus with their eyes fixed on the nearest tree. Soon, a flurry of hands pointed to the sky. Four birds with white wings flew overhead, and the students wrote down their findings -- their first as citizen-scientists in a global research project.

More than 100 students in first through 12th grades at the Germantown school participated in the 20th annual Great Backyard Bird Count, an international project to collect data on wild birds and post results in real time.  The census, spanning four days over Presidents' Day weekend each year, enlists volunteers to count birds wherever they find them -- in trees, on statues, along hiking paths, and flying above.

Scientists use the information for studies including migration patterns, habitat deterioration, and the effects of climate change.

"The collection of this data is critical because the scientists" can't do it alone, said Steven Saffier,  coordinator of  the Audubon at Home program at the John James Audubon Center at Mill Grove in Montgomery County. Audubon at Home helps communities transform their surroundings into bird-friendly places.

"This gets a lot of information to scientists quickly," Saffier said.

More than 160,000 people in at least 100 countries -- including at least 13,000 in Pennsylvania and New Jersey -- are expected to participate in the count, organized by the National Audubon Society and the Cornell Lab of Ornithology, a nonprofit that studies bird species and is affiliated with Cornell University.

Last year, 163,700 bird-watchers identified 5,689 species -- more than half the known species on the planet.

Participants count the birds,  identify them according to online guides, and then enter their findings on   The Great Backyard Bird Count is one of several similar citizen-driven bird censuses that include the Christmas Bird Count and Project Feederwatch.

Students at the Pennsylvania School for the Deaf were excited to do their part, said Theresa Yorgey, head of the high school and an avid bird-watcher.

"Obviously [the students] won't be able to identify the bird's song, but their sense of vision is heightened, so bird-watching is a natural fit," Yorgey said.

They had prepared for weeks, making sustainable bird feeders out of materials such as recyclable seltzer bottles. In an exercise to help them feel the sound vibration in a bird's call, they placed their hands on a styrofoam tube attached to a computer speaker as teacher Eric Greenberg clicked on sound files of birds.

During the school's daylong count, Saffier led an hour-by-hour presentation to help students identify birds,  and Carrie Barron, assistant  director of the Audubon Center, introduced them to Conrad, a three-year-old blue jay housed at the center.

Standing just inside the doors of the school's Maguire Student Center, Gizelle Gonzalez, 9,  spotted a Carolina chickadee in a nearby tree.  Jade Mack, 11, spied a red-winged blackbird.

Teacher Melissa Keeley described the bird count as a real-world application of what students learn in the classroom.

"Inside we do experiments," said Keeley, who heads the elementary school science department,  "but this is global science and active research. They are contributing to something way bigger than a class experiment."