As I'm recording this, autumn is just around the corner in the Northern Hemisphere. For me, that

means it's almost time to put my fuzzy sweaters back into heavy rotation and to start drinking

gallons of hot herbal tea, which I guess if we're not pronouncing the letter H, I should say ot herbal tea.

And autumn is also a time when I look wistfully out the window day after day at the rain-drenched

city of Portland, Oregon, thinking about the past and the future.

But for countless birds around the world, this is a season to move, to relocate.

Some will make epic migratory journeys of thousands of miles.

Others will travel only a few tens of miles.

Some birds migrate up or down in the vertical dimension,

along the slopes of mountains. Many birds move into habitats different from the ones where they

spend the summer. Meanwhile, other birds might just hunker down where they are, staying in

more or less the same location all year long.

All spring and summer we get to know certain birds in our backyards and our local parks.

In North America, familiar species include American Robin,

ruby-throated and Anna's hummingbirds,

Baltimore Oriole and Broad-Winged Hawk. In Europe, the songs of

nightingales and cuckus are familiar in the warm months. We recognize these birds at the species

level, but sometimes we even get to know individual birds. But sadly, many of them disappear from our backyards during the winter.

We miss them terribly and pine for them. Months go by. Then, as if by magic or in answer to our

prayers, the little buggers reappear the following spring. How can we figure out where our birds go and what sorts of

mischief they get up to while they're away? Well, scientists have been keenly interested in

such questions for hundreds of years. By tracking the movements of individual birds,

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