Takoma Park: A plump robin wearing a tiny metal backpack with an antenna hops around a suburban yard in Takoma Park, then plucks a cicada from the ground for a snack.
Ecologist Emily Williams watches through binoculars from behind a bush. On this clear spring day, she’s snooping on his dating life. “Now I’m watching to see whether he’s found a mate,” she said, scrutinising his interactions with another robin in a nearby tree.
Once the bird moves on at season’s end, she’ll rely on the backpack to beam frequent location data to the Argos satellite, then back to Williams’s laptop, to track it.
The goal is to unravel why some American robins migrate long distances, but others do not. With more precise information about nesting success and conditions in breeding and wintering grounds, “we should be able to tell the relative roles of genetics versus the environment in shaping why birds migrate”, said Williams, who is based at Georgetown University.
Putting beacons on birds is not novel. But a new antenna on the International Space Station and receptors on the Argos satellite, plus the shrinking size of tracking chips and batteries, are allowing scientists to remotely monitor songbird movements in much greater detail than ever before.
“We’re in a sort of golden age for bird research,” said Adriaan Dokter, an ecologist at Cornell University who is not directly involved with Williams’s study. “It’s pretty amazing that we can satellite-track a robin with smaller and smaller chips. Ten years ago, that was unthinkable,” he added.
The device this robin is wearing can give precise locations, within about 30 feet (about 10 metres), instead of around 125 miles (200 kilometres) for previous generations of tags.
That means Williams can tell not only whether the bird is still in the city, but on which street or backyard. Or whether it’s flown from the Washington, DC, suburbs to land on the White House lawn.
A second new tag, for only the heaviest robins, includes an accelerometer to provide information about the bird’s movements; future versions may also measure humidity and barometric pressure. These Icarus tags work with a new antenna on the International Space Station.
Scientists have previously put GPS-tracking devices on larger raptors, but the technology has only recently become small and light enough for some songbirds. Tracking devices must be less than 5% of the animal’s weight to avoid encumbering them.
In a Silver Spring, Maryland, yard, Williams has unfurled nylon nets between tall aluminum poles. When a robin flies into the net, she delicately untangles the bird. Then she holds it in a “bander’s grip” — with her forefinger and middle finger loosely on either side of the bird’s neck, and another two fingers around its body.