Unraveling the Secrets of Migration

September 17, 2023

A review by Lori Potter

Flight Paths: How a Passionate and Quirky Group of Scientists Solved the Mystery of Bird Migration, by Rebecca Heisman

HarperCollins Publishers, 2023

288 pages, hardcover

ABA Sales–Buteo Books 15328

Consider Winged Migration, the 2001 documentary that is still available for streaming more than two decades later; A World on the Wing, Scott Weidensaul’s bestseller of two years ago; and Wingspan, the wildly fashionable board and video game. The popular appetite for images and themes involving avian migration seems unquenchable. Picking up on that interest, Flight Paths: How a Passionate and Quirky Group of Scientists Solved the Mystery of Bird Migration dives into the science that seeks to answer all the many “how” and “why” questions about migration. And it lays out the answers, to the extent they are known, in a clear, accessible style.

Rebecca Heisman, a scientist by training, knows how to work her way through scientific studies and present them in an intelligible, even compelling way. She starts with a teaser about the first inkling that birds might actually travel long distances in seasonal patterns—not just hibernate in trees, as Aristotle expounded, or bury themselves in mud banks, as others believed in the sixteenth century. It is said that in 1822, a hunter in Germany killed a stork that was already impaled with a wood spear and that the wood and iron tip could be traced to Africa. Hence, it was reasoned, the bird had migrated between the two continents. Whether the stork story is apocryphal is left to the reader. In a sense, it doesn’t matter, because it is this anecdote that switches on the science side of the brain and readies the reader to analyze the content that is to come.

What follows are pieces of a science jigsaw puzzle that Heisman takes evident pleasure in putting together. She organizes the book into nine chapters, each of which chronologically traces the use of a different technology to research avian migration, starting on the low-tech end with banding. Indeed, the low-tech methodologies she describes are entertaining, such as “moon watching,” where an observer identifies the silhouettes of migrating birds as they pass in front of an ideally full moon. There was also an era of counting and categorizing birds solely by their nocturnal flight calls.

The pace of change in the technology applied to bird migration studies increased exponentially around the end of World War II. Until then, radar could be used to detect “blobs of birds” but not the species, their starting and end points, or much else. Thanks to Heisman’s extensive end notes, the actual use of terms like “blobs of birds” is documented, along with all the other arcane terminology and step-by-step developments in a field that relied heavily on technology developed for war, weather, telecommunications, and other pursuits less sublime than ornithology.

A particularly cinematic sequence of Flight Paths involves the original use of radio transmitters glued to a bird’s back and the swashbuckling characters who followed specific birds for days on end. Those who gave chase by truck with an antenna sticking out the window had encounters with law enforcement. The daredevil scientist who followed birds in a small, shaky plane once radioed in his will during a nasty storm.

The need for individual human trackers, charismatic though they were, gave way in 2014 to radio telemetry with the launch of the Motus Wildlife Tracking System, a network of towers in North America. Radio telemetry used a bird-mounted Nano Tag weighing seven-thousandths of an ounce, a battery that lasted a few weeks, open-source software, and off-the-shelf receivers to create a network of shared data. While valuable data followed, the short battery life imposed real limits on the research of migration, and the next generation of science used solar-powered transmitters and receivers via the Argos satellite system, so that the entire flight paths of birds such as godwits and sandpipers doing trans-Pacific trips could be traced to learn where the birds stop over, in the interest of trying to protect enough of that habitat.

This back and forth between human researchers and ever more sophisticated technology is the heart of Flights Paths. While the book acknowledges the obvious population crisis of migratory birds, it urges perseverance under the credo “to save them we must know them.” There is much here, and not just for the science nerd. Flight Paths informs us and charms us by turns—all of us.


Lori Potter practices conservation law, writes for a variety of publications, and combines birding and bicycling at every opportunity. For Birding magazine, she has contributed several book reviews and a profile of Dorian Anderson's Big Year by bike. Lori is based in Denver, Colorado.