The massive annual spring migration of America's birds – millions of them – is underway. Here's how to follow along at home.

The massive annual spring migration of America's birds – millions of them – is underway. Here's how to follow along at home.

The massive annual spring migration of America's birds – millions of them – is underway. Here's how to follow along at home.

“The ruby-crowned kinglet, swamp sparrow and eastern phoebe are ... In North America, birds typically fly south for the winter before food is less available during the colder months, then ...

“The ruby-crowned kinglet, swamp sparrow and eastern phoebe are ... In North America, birds typically fly south for the winter before food is less available during the colder months, then ...