Season 8, Episode 23: Migration

"So, there's this bird. Some sort of swallow I think. Every September, thousands of them ditch rainy Seattle to winter in Mexico. These birds aren't dumb. And every year, rounds of people gather around in Seattle to drink beer and watch the flock take off. They call it the Great Migration."

"I don't know how those birds do it. Travel thousands of miles without getting lost. Banging into windows, being eaten by cats. But every spring, they're always here. I guess they come back to what they know. People say it's pretty cool, watching them go. They say you can actually see the moment when, at some mysterious signal, all at once the birds decide to leave. Whatever... there's always next year."

Source: http://www.meredith-and-derek.com/quotes/166