The maps show the paths the animals take as they cross desert, forest, ice, and ocean to feed, breed, and survive. The maps reveal what Audubon couldn’t see when he tied his silver thread to the birds: a journey. Some are especially quirky, as in the case of the seagulls who made daily trips to a city in France that was 40 miles away from their breeding colony. When researchers visited the site to investigate, they found the gulls feasting on discarded food outside of a potato-chip factory.

I spoke with Uberti and Cheshire about animal-tracking technology and the strange places it takes us. Our conversation has been edited for length and clarity.

Marina Koren: So your book introduces us to a fairly new era of tracking animals using technology. Can you tell me about the era that we’ve left behind? How did humans track animals before they could stick GPS tags on them?

Oliver Uberti: Until fairly recently, tracking involves looking for footprints, looking for fallen feathers, broken branches, droppings—any sign that an animal has passed through. Then around the past couple centuries, you start to get people like John James Audubon, who are tying threads to the legs of songbirds to prove that they’re actually returning to the same place every year. And then in the 20th century, you start to get people doing some real DIY tracking where they’re attaching cameras to pigeons or radio transmitters to a duck. But it’s only really been in the past 20 to 30 years that GPS has come on the scene, and then after that the miniaturization of computing power and the internet and satellites—it’s literally just exploded what you can do in a really tiny device.

James Cheshire: We’ve really transitioned from monitoring animals as a resource to be exploited to monitoring them as individuals within a species that we can collect a myriad of data from. Prior to the animal-tracking revolution, one of the biggest data sets collected on whales came from where we killed them, from whaling ship logs. There’s now sensors that they’ve got on whales that collect more data points than the sum total of the data collected in the previous five decades or more of research.

Koren: What kind of technology do we use today?

Uberti: There’s really no “one size fits all.” Scientists tailor tracking tags to the species and to the study, and that all depends on the environment that the animal lives in. GPS doesn’t penetrate underwater, so if you’re tracking a marine animal like a shark or a turtle, you need to have a device that can transmit when the animal comes to the surface and gets a brief, sometimes split-second window to shoot up to a satellite and transmit. Or you need a device that can release off the animal and float to the surface and then transmit. If you’re talking about songbirds, there’s protections in place to make sure they’re not taking tiny little songbirds that weigh only a few grams and saddling them with a giant computer. You talk about tracking plankton—you’re not even using a computer. You’re setting up an environment in an aquarium, you turn off all the lights, and you inject the plankton with a fluorescent particle like they use to track cancer in some medical technologies. And in the darkness, the individual plankton fluoresce and, by recording that with cameras, [scientists] can watch the illuminated animals move up and down the water column in response to UV light.