Motus: A Revolution in Migration Research

This bobolink’s nanotag was affixed with a leg loop harness and rests on the bird’s back like a backpack. In addition, color bands on the bird’s legs enable biologists to tell this individual apart from other bobolinks on their nesting grounds, when viewed through binoculars. Photo by Noah Perlut.

For more than a century, biologists have utilized bird banding for studying avian migration, survivorship, longevity, and reproductive success. It’s an essential tool, but one with a significant limitation: in most instances, birds need to be recaptured in order to read the unique codes on their bands, and the chances of re-sighting a banded bird are incredibly low. Since 1960, more than 40 million songbirds have been banded in North America, but only 1.4 percent were ever recorded again.

Over the past few decades, GPS, satellite, and cellular transmitters have provided more detailed information on bird movements and allowed biologists to retrieve data without recapturing individual birds. However, these technologies are limited – with few exceptions – to larger species that can safely support the added weight.

Technician Todd Alleger attaches antennas to a freestanding Motus receiving station on conservation land in southwestern New Hampshire. Photo by Brett Amy Thelen.

Enter the Motus Wildlife Tracking System, an international research network that is taking the study of winged migration by storm. Named after the Latin word for “motion,” Motus comprises tiny radio transmitters (“nanotags”) – which are affixed to small birds, bats, and even some insects – and a network of receiving stations that detect the radio signals whenever a tagged animal flies within range.

Although it’s existed for less than a decade, Motus has already yielded meaningful data about migration routes, timing, flight speed, stopover behavior, locations of critical migratory and overwintering habitat, and more. From 2014 through 2017, for instance, Motus researchers discovered that a substantial portion of the globally endangered red knot population migrates through Pennsylvania en route to their Arctic breeding grounds each spring – data that now informs siting of ridgetop wind farms.

Individual fall migration paths, as detected by the Motus Wildlife Tracking System. The rusty blackbird flew 1,054 miles over 160 days, from Tadoussac, Quebec, to Tannersville, Pennsylvania. The dragonfly flew from Ontario to Cape Cod – more than 850 miles – in just seven days. The red knot migrated nearly 6,000 miles from Hudson Bay to French Guiana in less than a month, including a 19-hour flight from Churchill, Manitoba, to southern New Hampshire. The bobolink flew 3,035 miles from Maine to Colombia over 32 days, and is the first of its species to be detected by Motus antennas outside North America; its final destination may be the grasslands of southwestern Brazil, Paraguay, northern Argentina, or central Bolivia, although it’s unlikely to be detected there, as very few Motus stations currently exist in interior South America. Graphics by Steven Lamonde.

Researchers in New Hampshire carefully attach a radio tag to a rusty blackbird, a species that has experienced precipitous declines since the mid-1990s. Motus is helping ornithologists learn more about migration timing, stopover sites, and wintering habitat of this vulnerable North American bird. Photo by M. Jensen.

“It’s the ultimate in collaboration,” says Amber Roth, a biologist from the University of Maine who uses Motus to study golden-winged warblers, Bicknell’s thrushes, and bobolinks, among other species. The more stations in the network, the better the chances of encountering a tagged animal. Every station contributes to the whole, whether or not animals are tagged there. While some data are only available to researchers, anyone can access tag detections and information such as flight paths for individual birds at motus.org, an archive managed by Birds Canada.

Initial work concentrated primarily on Atlantic, Gulf of Mexico, and Great Lakes coastlines, but a new project aims to establish a series of east-west receiving station “fence lines” to detect tagged wildlife as they migrate north-south through interior New England.

So far, the New England Motus project has added 24 stations on both private and public land in New York, Connecticut, Massachusetts, Vermont, New Hampshire, and Maine, with plans to add another 26 by 2023. Antennas have been installed on windmills, barns, nature centers, old telephone poles, and freestanding towers in fields and other clearings, secured by guy wires and powered by solar panels. It’s an effort Marc Nutter, conservation program director for New Hampshire Audubon, describes as “herculean.”

Motus tags range from 0.13 to 3 grams in weight. The larger the tag, the larger the battery, the longer it lasts. Tags used on monarch butterflies may only transmit data for weeks or months, while tags used on large birds can span a year or more. Photo by Grace Pitman.

One of the goals of a new bobolink study led by Roth and Noah Perlut of the University of New England is to pinpoint important migration routes and stopover habitat at a higher geographic resolution than was possible before. Their Motus data will also inform local conservation efforts, such as identifying when bobolinks depart their grassland breeding grounds in order to determine safe haying dates for working farms.

“We have not yet analyzed the data,” cautions Perlut. “That said, one of the most exciting things we’ve learned so far from [bobolinks tagged in the spring and summer of 2021] is the massive importance of the Blackwater National Wildlife Refuge in Maryland. Approximately 25 percent of the 40 birds we tagged spent time on or near that refuge [during their fall migration], some of them staying there for up to 10 days. These data are incredibly informative for thinking about refuge management, and potentially management of adjoining properties as well.”

“The information we’re getting through Motus is redefining our understanding of migration,” reflects Roth.

With nearly 1,300 receiving stations across 31 countries and more than 30,000 tags deployed to date, the conservation potential of Motus is enormous, as is its power to connect people and places that once seemed distant. In tracing any one of the migration maps found on motus.org, we quickly see that “our” birds are “their” birds, too.