The Lewis’s Woodpecker is one of the West’s avian gems. It has a ruby-red face and emerald feathers draped across its back like a cape with a silver cowl. In summer it swoops and circles over woodlands west of the Great Plains, performing aerial acrobatics as it hunts insects on the wing. While wintering in forests of the far West and Southwest, it aggressively defends caches of stored nuts from piratical Acorn Woodpeckers. Captivating as it is, however, there is still much we don’t know about the bird’s movements and biology—or what has driven its population to decline by about half since the 1960s.

To figure out what’s spurring the losses, scientists at MPG Ranch, a conservation research group in western Montana, are tracking Lewis’s Woodpeckers with a simple and increasingly popular technology. Since 2019 they’ve attached radio transmitters to birds breeding in the Bitterroot Valley. When a tagged bird passes within a dozen miles of one of 13 receiver stations in the 96-mile-long valley, its identity is automatically logged at the antenna location, revealing its movements on its breeding grounds. Individuals tagged in the Bitterroot have also pinged tracking stations in southwestern Oregon, providing new information about where the birds go in winter. The technology is painting a fuller picture of the woodpeckers’ annual movements, says MPG Ranch biologist William Blake, and helping to pinpoint where they might be running into trouble from logging, wildfires, or other threats—and thus where to focus conservation efforts.

The Lewis’s Woodpecker is one of hundreds of species that scientists are remotely monitoring with the Motus Wildlife Tracking System, which went online in 2015. Named after the Latin word for movement, Motus uses arrays of automated radio receiver stations to detect tagged animals over vast distances. Today some 1,500 receiving stations are active around the globe. Scientists have affixed tags to more than 34,000 animals, from birds and bats to butterflies and bumblebees.

The Motus network is overseen by a team at the nonprofit Birds Canada including longtime migration scientist Stu Mackenzie, who helped pioneer the system with Acadia University researchers in the early 2010s. While scientists have used radio telemetry to track animals since the 1960s, recent technological advances have ushered in miniature tags weighing as little as a coffee bean. These tags can be attached to songbirds as small as Canada Warblers or Gray-cheeked Thrushes—and even tinier insects. In addition to studying their movements, scientists can analyze tag data to glean details like when a bird is active, when it’s sleeping, and when it takes flight.

In the past scientists had to track radio-tagged animals with cumbersome handheld antennas, stalking them across the landscape to get within signal range. Now with Motus, a vast community of collaborators have assembled a global network of stationary, inexpensive radio receivers that can passively pick up signals from any tagged animals nearby.

“You can put a Motus station on just about anything,” Mackenzie says. Many are stand-alone towers. But they’ve also been attached to telephone poles, weather stations, ships, lighthouses, high school roofs, and, near Tucson, Arizona, an inactive windmill. One thing these locations all have in common: a clear view of the sky, to best pick up signals.

When a bird passes by a receiving station, a computer records and stores the unique radio ID from its tag. Many stations upload these data directly to the Motus database housed at Birds Canada’s National Data Centre in Ontario. This centralized database is the final innovation underlying Motus’s success. It connects all antennas from around the world and makes the information freely available to researchers and the public at

Every tracking technology has its pros and cons. GPS tags, which have been deployed since the mid-1980s, are the most geographically accurate, but they’re heavy and expensive. Geolocators, half-gram sensors that estimate location from light intensity, came on the scene in the early 2000s, allowing researchers to follow songbirds for the first time. But they also have a catch: You must recapture a bird to recover the data stored on the gadget, and the majority of birds are never recaptured.

With Motus, there’s no need to spend days or weeks in the field trying to catch birds that had previously been tagged. What’s more, the system harvests data in real time. “I can sit in my office at a university or at an Audubon facility, and the data come to me,” says Cristina Francois, former director of Appleton-Whittell Research Ranch of Audubon, which erected a station in Arizona in March.

Motus’s main limitation is the number and density of stations. Receivers span from as far north as Canada’s Northwest Territories to as far south as the southern tip of Chile, but most are concentrated in eastern areas of Canada and the United States. There are markedly fewer in South America, where many migratory birds overwinter. “The actual range of a Motus station is quite small compared to the vastness of the landscape,” Mackenzie says. “There are many gaps in the network.”

When structures are far apart, scientists are stuck making educated guesses as to the routes birds take. So they’ve adopted a strategic approach in placing some stations to get the most bang for their Motus buck. A chain of four stations spanning the Isthmus of Panama, for example, could detect almost any tagged animal flying overland through the narrow corridor, revealing which birds follow this course between North and South America.

Motus is complementary, not competing, with other tracking tools, says Mackenzie: “We want all these technologies to be working together to solve the problems that we face.” It’s a daunting challenge. Across their annual cycles migratory birds encounter habitat destruction, pesticides, predators, extreme weather, and many more threats to their survival. Knowledge of birds’ locations—an endangered species’ flight path or areas preferred by flocks—is integral to safeguarding them year-round.

Motus data can help show policymakers how to prioritize funding and target areas for protection. For instance, many of North America’s grassland birds winter in the Chihuahuan Desert in the southwestern United States and northern Mexico. But farms and ranches are overtaking valuable habitat. The new Motus station at Appleton-Whittell Research Ranch is part of a project led by Bird Conservancy of the Rockies (BCR) to study how declining species like Grasshopper Sparrow use the remaining Chihuahuan grasslands. “Which ones are the most important for conservation efforts to best serve the needs of these birds?” says Matt Webb, a BCR avian ecologist. Motus will help him find out.