Should you spy a robin wearing a backpack, don’t be surprised. That backyard birdie could be helping scientists study animal migration.

The American robin is an iconic North American songbird. Its cheerful chirp is a sure sign of spring. And although God knows every bird’s flight and fall, (Matthew 10:29) the robin’s migration habits remain a mystery to human scientists.

“It’s astounding how little we know about some of the most common songbirds,” says scientist Ken Rosenberg. “We have a general idea of migration, a range map, but that’s really just a broad impression.”

Ecologist Emily Williams studies the yearly migration of American robins. As a scientist, Williams wasn’t captivated by the birds’ striking plumage or sweet songs but their extraordinary travels.

“Realizing that this tiny animal that can fit in the palm of your hand can travel thousands and thousands of miles one way in spring, and then [do] it again later in the year, was just amazing to me,” she says. “I have always been dazzled by migration.”

Williams hopes to gather information about nesting in robin breeding and wintering grounds. She already knows some robins fly nearly 3,000 miles between their breeding area in Alaska and winter grounds in Texas—while others hop around a single backyard most of the year. She wants to know why.

As part of her study, Williams catches a robin and carefully measures its beak. She clips a toenail and plucks a tail feather. These samples will help her gauge the bird’s overall health.

Then she weighs the bird. On average about 80 grams, a robin weighs the same as four large strawberries. That’s just sturdy enough to carry a penny-sized satellite tag.

Williams fashions a makeshift “saddle” with clear jewelry cord. The saddle will hold the tag. When Williams releases the robin, it flies off. The tag beams location data to a satellite. Then Williams downloads that information to a laptop. The tracker gives locations within about 30 feet. Williams will be able to tell not only whether the bird is still in the city, but also on which street or in which backyard. Previous tags were accurate only to within about 125 miles.

Trackers on birds aren’t new. Scientists have put GPS-tracking devices on larger birds, but the technology has only recently become light enough for some songbirds.

“We’re in a sort of golden age for bird research,” says ecologist Adriaan Dokter. “It’s pretty amazing that we can satellite-track a robin with smaller and smaller chips. Ten years ago, that was unthinkable.”