16 January, 2023
The White Stork provided people with the first physical evidence of long-distance bird migration. Photo by Nico Arcilla.
Bird migration has captivated the human imagination and challenged scientific understanding for thousands of years. In the fourth century B.C., Aristotle theorized that the annual disappearances of birds in winter might be explained by birds’ hibernation or by their temporarily transforming themselves into other bird species. Not until 1822 did the breakthrough come that provided evidence of the real story, when a German hunter shot a bird which, amazingly, had previously survived being shot in Africa. How did they know? The White Stork (Ciconia ciconia) had been impaled by the arrow of an African hunter but nevertheless had flown over 5000 km to the German coast of the Baltic Sea, providing the first physical proof of long-distance bird migration between Europe and Africa. Since this breakthrough, scientists have used many methods to study bird migration, but an enormous number of mysteries remain.
The Wilson's Snipe has a huge range in the Americas, but little is known about its migrations. Photo by Nico Arcilla.
Wilson’s Snipe (Gallinago delicata) provides a case in point. Most Wilson’s Snipes nest in North America and migrate with the seasons, including long distances to the Caribbean and South America. During migration, they travel in flocks on moonlit nights, especially during the first and last quarters of the moon. In spring, males migrate before females, while in fall, females migrate before males, a phenomenon known as “differential migration,” where birds of different sexes and ages show different migratory patterns. This has been observed in many bird species, but is still not well understood by scientists. Despite its huge range, Wilson’s Snipe is elusive and poorly studied species that was only recognized as a separate species from its Eurasian cousin, the Common Snipe (Gallinago gallinago), 20 years ago. Because it is often cryptic and difficult to observe as well as among many species of birds that migrate at night, understanding its migratory behavior presents a challenge. But now, new technologies and research networks are enabling scientists to address knowledge gaps about migratory birds in ways never before possible.
New Motus stations in Nebraska add to a previously existing network of Motus stations tracking migratory birds in the Americas. Map by Rachel Kaplan.
One example is the Motus Wildlife Tracking System, an international collaborative research network that uses automated radio telemetry to track the movements of animals tagged with miniature transmitters (nanotags). IBCP is pleased to have contributed to the inclusion in this network of the University of Nebraska’s Cedar Point Biological Station, which recently established a Motus station thanks to a generous grant from the Cooper Foundation. How does it work? Motus nanotags on study species may be detected by more than 700 receiving stations, most of which are located in eastern North America. Motus stations include a power source, receiver, and antennae that detect tagged birds that fly within 15 km.
A Western Meadowlark (Sturnella neglecta) carrying a nanotag is detected by a Motus receiving station. Illustration by Rachel Kaplan.
The Cedar Point Motus station enables scientists to detect tagged birds using the Central Flyway, one of the most important migratory bird pathways in the world. Motus nanotags are attached to birds using miniature backpack-like harnesses. Due to technological advances, these tags range in size from only 0.2 to 2.6g and have lifespans of up to three years, depending on size (smaller batteries have shorter lifespans) and how often a radio pulse is transmitted. Motus nanotags allows us to track songbird migrations to an extent not possible until now. The closest stations to the north and south of Cedar Point are located approximately 1200 km and 550 km away, respectively. In the first months following its establishment, the Cedar Point Motus station picked up signals from migratory birds of four species, including Swainson’s Thrush (Catharus ustulatus), Black Tern (Chlidonias niger), Sprague’s Pipit (Anthus spragueii), and Greater Yellowlegs (Tringa melanoleuca).
The first migratory birds detected by the Motus station at the University of Nebraska’s Cedar Point Biological Station. Map by John DeLong.
While the importance of protecting Great Plains habitats for migratory waterbirds such as Sandhill Cranes (Grus canadensis) and Snow Geese (Anser caerulescens) is already well-known, these findings highlight their use on less conspicuous migrations by songbirds and shorebirds. The Greater Yellowlegs, for example, like Wilson’s Snipe, has a huge range in the Americans, but our knowledge of its migrations is limited. We know that Yellowlegs are among the first birds to arrive at their sub-Arctic nesting grounds and that they may winter as far south as Chile. We also know that Greater Yellowlegs, like Wilson’s Snipes, show patterns of differential migration. Both female snipes and yellowlegs leave the nesting grounds to migrate before males at the end of the breeding season, but whereas juvenile snipes appear to migrate before adults, yellowlegs adults appear to migrate before juveniles. What drives these patterns remains a puzzle – one of many mysteries of bird migration that insights derived from the Motus network may help us solve.
A Greater Yellowlegs. Photo by Dan Marks.