In 1250, the prior of a Cistercian Abbey reputedly tied a note to a leg of a barn swallow, which read: “Oh swallow, where do you live in winter?” The next spring, he got a response: “In Asia, in the home of Petrus.”

This perhaps apocryphal story marks one of the first known instances of someone tagging an animal to track its movements. Thanks to many such endeavors, we now know that every year, barn swallows migrate between their breeding grounds in the northern hemisphere to wintering grounds throughout the tropics and the south. In 1912, one intrepid individual that was ringed in England turned up 7,500 miles away in South Africa.

But swallows are the exception rather than the rule. The journeys of most migratory animals, especially smaller species, are a mystery. Flocks, herds, and shoals are constantly crisscrossing the globe, but despite the intense surveillance of our planet, we often have no idea what paths they take. “They leave in one place and we don’t know what happens to them until they show up in another place,” says Meg Crofoot from the University of California, Davis.

This ignorance makes it hard to save threatened species: what works in one part of the world may be completely undone as animals travel to another. It also jeopardizes our own health. Where are the birds that harbor avian flu? Where do the bats that carry Ebola go? What about the red-billed quelea, a small finch that flocks in millions and devours crops with locust-like voraciousness?

Since the 1960s, scientists have tried to answer questions like these by tagging animals with radio transmitters. At first, they followed the signals with clunky hand-held antennae; later, they loaded receivers onto satellites, allowing them to track animals over long distances and rough terrain. But even after decades of innovation, satellite telemetry tags are still expensive, slow, and clunky. The smallest weighs around 10 grams and would overburden any animal lighter than 240 grams. That rules out three quarters of birds and mammals. There are much lighter data-loggers around but they’re light because they don’t transmit any data—so you have to recapture whatever animal you’ve tagged to find out where it has been.

Frustrated by these limitations, Martin Wiselski at the Max Planck Institute for Ornithology devised the ICARUS Initiative (International Cooperation for Animal Research Using Space). His team has developed extremely light radio tags that can be fitted to even tiny animals, and they’re sending a dedicated receiver to the International Space Station next summer. Once it’s up, it will be able to map the whereabouts of hundreds, if not thousands of birds, bats, and other travelers, in real-time. “It will be the best ever possible sensing network of life on the planet,” says Wiselski.

He came up with the idea while talking to astronomer George Swenson, who helped to pioneer the use of radio telemetry for tracking wildlife, and who also helped to construct the radio telescope known as the Very Large Array. “We were sitting on some stairs in Panama, having beer, and looking over the canal,” says Wiselski. “I said there must be a way to receive these small transmitters from all over the globe. George said this is what we do all the time—build telescopes to look at small radio sources. We look up into the sky. You need to look at the ground.”

Still, Swenson predicted that it would take 15 years to get the system up and running. Wiselski told him he was being ridiculous. That was 15 years ago. (The Icarus myth, after all, is more about hubris than flight.) Getting funding was the hardest part. “We went to NASA,” says Wiselski. “They thought the project so unlikely that it was set in the same category as the space elevator.”

The team eventually secured 19 million euros from the German Aerospace Center, as well as 1.7 million euros from the Max Planck Society to make very small tags. The first-generation models will weigh 5 grams but the team wants to get them down to just one, which would allow them to track even the lightest fliers like swifts. Each tag comes equipped with a solar panel, GPS, and a huge memory, and can measure acceleration, temperature, bearing, pressure, light intensity, and more. Unlike the smallest current data-loggers, they can transmit information, too. They can even be reprogrammed from space.

Eager researchers are already lining up to use the tags. To begin with, between 40 and 50 teams will use ICARUS to study birds, bats, sea turtles, and more. All the data from this work will eventually be uploaded to MoveBank, a free online database for animal tracking studies. “It’s a big data project for life on the planet,” says Wiselski.

Roland Kays from North Carolina State University is especially interested in bats. In North America, tree bats are hit by windmills at a surprisingly high rate. “They migrate, but we don’t know where they’re going,” says Kays. “By understanding their routes, we can decide where to put turbines, or just turn turbines off for a few weeks when the bats are moving through.” Another group is using the tags to track orangutans. “A lot of money gets poured into relocating them, and releasing them into the wild,” says Crofoot. “But we don’t know where they go once we let them go.”

By tracking animals, researchers may also be able to discover the secret pathways and hiding places of viruses and other pathogens. Consider Ebola: the identity and location of its wild reservoirs are still hotly debated, although it seems that certain bat species can harbor it. “We can take a blood sample and check if they have Ebola, put tags on them, let them go, recapture them and take another sample,” says Wiselski. “We can then say that bats that have been through this part of the Congo have seen Ebola.”

Beyond charting the movements of animals, Wiselski thinks that ICARUS could be a deterrent to those who would stop animals from moving altogether. If wildlife managers start tagging elephant ears or rhino horns, it might deter poachers from killing the animals and transporting their body parts, lest they in turn be tracked by overhead satellites. “We have request from people in Mongolia, because people are stealing the bones from the dinosaurs,” adds Wiselski.  

And just as ICARUS will provide researchers with information about animals, the animals will in turn provide them with information about the planet. “We can consider the animals as sensors,” says Kays. Using hearing, smell, vision, and more esoteric senses like magnetoreception, they detect and react to changes in their environment. They’re like a living fleet of thermometers, barometers, and more; through their movements, they reveal the world—as in the case of the red knots I recently wrote about.

Controversially, Wiselski suspects that some species might even be able to predict disasters like volcanic eruptions or earthquakes. “There’s a lot of anecdotal evidence, but I think there’s something to it,” he says. “We have to do a lot more research obviously.”

“The tech is finally at a state where this is all possible. We all carry GPS trackers in our pockets and purses,” says Crofoot. It also helps that science is becoming increasingly international, making it easy for aficionados of animal movement to migrate towards each other. An International Bio-Logging Society has just formed, and they plan to start a “Decade of Bio-Logging” in 2018. Meanwhile, Wiselski is in talks with other space agencies about putting ICARUS payloads on their satellites, or even to build a bespoke ICARUS network. It’s a far cry from handwritten notes on swallow legs.