From border to border, Pennsylvania is a state full of forests, mountains and hills, and the valleys and floodplains of rivers that have carved them. Lake Erie laps at the northwest corner of the state (think gulls and shorebirds), and in the southeast is Pennsylvania's piedmont. In between, the Appalachian Mountains curve through, channeling migrating songbirds to and from breeding grounds farther north. One such ridge is Hawk Mountain, perhaps the best-known hawk watch site in the world. The Atlantic Flyway encompasses the state, and Pennsylvania, boasts 433 species documented in eBird.