Tag and Release: Tiny Tech Traces a Rare Bird's Path

Geolocator devices offer an unprecedented window into shorebirds' flight paths and patterns—if you can find them again.

Shorebirds in flight (Jan van de Kam, NL)

I first saw Y0U on the Delaware Bay. That is, Y-zero-U, the alpha-numeric code used to identify a banded shorebird. This particular bird, a member of the rufa subspecies of red knot (Calidris canutus), is the focus of an ongoing effort to attach geolocation recording devices to these small, long-distance migrants as a means of tracking their movements throughout the Western Hemisphere.

Roughly the size of a robin, these birds forage on the shores of the Bay by the thousands each spring, outfitted in their reddish breeding plumage and on their way north to nest.

Part of an initial cohort of 47 Delaware shorebirds outfitted with geolocators in May of 2009, Y0U was one of the few re-captured the following year—giving wildlife researchers an unprecedented window into the flight paths and patterns of an animal currently being considered for “threatened” status under the U.S. Endangered Species Act.

Kristoffer Whitney

I was on the Bay as a volunteer and observer, doing research for a dissertation in the history and sociology of science.  Shorebird research, particularly on the imperiled red knot, seemed a perfect case study on the interactions between science and policy in North America.  I wanted to understand this research within a broader history of U.S. wildlife conservation.  But I also wanted to understand the nitty-gritty processes of knowledge generation on the shores of the Delaware. The teams of scientists banding shorebirds there shared with me their techniques, of course, but also the variety of hopes, anxieties, and expertise that motivated and shaped their research.

Systematic, scientific bird-banding in North America goes back to the early 20th century. Spearheaded independently by numerous local and regional ornithological associations, the practice of affixing birds with individually encoded bands was centralized under the authority of the Federal government in 1920. Originally housed in the U.S. Biological Survey, a forerunner of the Fish and Wildlife Service, today the “Bird Banding Laboratory” is located at the Patuxent Wildlife Research Center in Maryland, under the auspices of the U.S. Geological Survey. According to the Center, over the past decade alone over 1 million banding records have been received per year.

Banding shorebirds like red knots on the Delaware Bay has been carried out by New Jersey and Delaware state wildlife managers, biologists, and interested amateurs for several decades now, but adding individually-coded, colored “flags” to birds like Y0U and K0H (pictured above) began in 2003. Light-level geolocators provided by the British Antarctic Survey, able to record the actual flight paths of shorebirds, were a much more recent innovation—awaiting a degree of miniaturization that would work for these smaller animals. The complicating twist, however, is that unlike satellite transmitters used on larger birds, these “dataloggers” have to be re-captured. In other words, once you tag a bird and let it go, you have to catch it again a year later, manually remove the geolocator, and download the data.

This is no simple task. I first joined teams of shorebird researchers on the Bay during the spring migrations of 2009. My very first catch was a foggy morning on Reed's Beach, New Jersey. The team was led by Mandy Dey, the principal zoologist for the State's Endangered and Nongame Species Program, and Larry Niles, retired Chief of the same Program. Their team varies somewhat from year to year, but includes a core group of academic, state, and avocational experts—some traveling internationally on “busman's holidays” to take part in the Delaware Bay migratory phenomenon. As an interested amateur working on a graduate thesis, I was given step-by-step instructions as we readied a “cannon net” on the beach. These large nets are buried and camouflaged in the sand, the projectiles on their leading edge fired from black-powder “cannons” over flocks of unsuspecting shorebirds that wander into the catch zone.

I remained huddled behind sand dunes with other volunteers while Niles watched the beach for conditions suitable for a safe catch. Dey spoke with us while we waited, giving us a rough idea of what to expect and reassuring us that though there were likely to be some, say, harsh directives for keeping the catch safe and efficient, we shouldn't become rattled or take it personally. When the cannons went off, I found myself racing down the beach and into the surf around a “wet catch”—an instance in which the net fires partway onto the water, necessitating a quick recovery so that all the pinned shorebirds are moved onto the sand as soon as possible. Once on the beach, we covered the hopping, chirping mass of net with covering material to protect and calm the birds, and began moving them to shaded “keeping cages.” Once secured, we passed each shorebird around a small circle of researchers, each responsible for a different task: taking various biometrics, affixing bands and flags, and keeping careful records.

Jan van de Kam, NL

It was a few days later on a beach a little further up the Bay that I helped catch part of the first cohort of red knots to carry light-level geolocators. These one-and-a-half gram data-loggers have already paid dividends in new data, but this was by no means certain at the time. Each release of a shorebird was and is an act of faith, albeit a carefully considered and monitored one. I watched as a subset of the red knot catch was outfitted with their leg-mounted tech, and then placed under a “tent” for observation. If Rutgers behavioral ecologist Joanna Burger gave the okay, according to protocol, the birds were presumed unaffected by the catch and new gear, and released.  In other words, each red knot fitted with a geolocator was given a clean bill of health before being released.  The hope was that at some point in subsequent migratory travel between the Arctic nesting sites and South American wintering grounds, these same red knots would be re-trapped, and the data recorded in their geolocators downloaded for analysis.

As it turned out, three of the 47 red knots initially fitted with data-loggers on the Delaware Bay that year were recovered the following spring. It may sound like a puny recovery but given that this was the first attempt to release and recapture geolocator-equipped red knots from the Bay, each bird was celebrated as a success. Among them was Y0U, leaving the Delaware Bay at the end of May, 2009, flying to James Bay, Ontario, and then on to Southampton Island, Nunavut, Canada to (hopefully) nest. The southbound trip later that summer included some surprises, presumed to be the result of severe storms that year, including a “backward” northern flight from New Jersey to Cape Cod and a stop in the Lesser Antilles, before wintering in northern Brazil. Though Y0U's geolocator stopped recording prematurely on the Brazilian wintering grounds, it was re-captured on its northward migration through the Delaware Bay on May 14, 2010. In all, Niles and his team estimated that this particular shorebird had covered more than 17,000 kilometers—that’s 10,500 miles—over the course of the year.

Subsequent studies have told similar stories about the few red knots captured, fitted with geolocators, and re-captured throughout the hemisphere. Similar, but not exactly the same. As the same research team in a later study involving eight red knots recovered on Cape Cod put it: “To date, all studies of shorebirds using geolocators have changed our conceptions about their migration strategies and the sites they use. This study is no exception. It has revealed previously unknown stopover and wintering sites and a surprising lack of commonality between the eight focal birds in their migratory pathways.” While in theory geolocator-outfitted red knots serve as proxies for an entire subspecies, thus far each bird has had its own, surprising story to tell. While these surprises are valuable, they also indicate a need on the part of scientists for more research until stronger patterns emerge. As the study concludes: “it will be very difficult to reach firm conclusions about the [migration] strategies of the whole population without a lot more data.”

Data-loggers have added more than surprises, however, providing continuity and meaning to known migratory stopovers. Research sites that were once brief windows onto the phenology of shorebirds have become part of a more fluid, connected narrative. As Niles recently blogged from Brazil: “Even the most seasoned shorebird biologist is thrilled to follow one bird’s movement as it leaves its Arctic home and muscles thousands of miles to one or more stopover sites on its way to a comfortable winter. Our team sees these birds in many of these places, including Delaware Bay, Cape Cod, Georgia’s barrier islands, the Caribbean leeward islands, and San Antonio Oeste, Argentina, to name a few. Our experience at these stopovers puts flesh on the bones provided by the geolocators so we can knit together a journey, an experience, a life of a wild animal.” Which means that even the newest geolocation technology is being used for a classic kind of research. Today’s style of natural history would indeed have been recognizable to wildlife biologists in the Biological Survey a century ago—though the miniaturized Space Age tools and cutting-edge computer modeling may have astounded them.

Valuable and meaningful geolocator results notwithstanding, the intended and unintended consequences of these hybrid technologies and human/nonhuman collaborations remain to be seen. This is particularly apparent when it comes to conservation, the ostensible reason for all this research. Shorebird study at major stopovers like the Delaware Bay intensified greatly in the 1990s in response to a new, large-scale fishery on the East Coast: trawling and hand-harvesting Atlantic horseshoe crabs to be used as bait in the eel and conch fisheries. In addition, and subject to much press of late, has been the use of horseshoe crab blood in the biomedical industry. This industry has come under strict regulation in the United States, particularly in New Jersey, because eggs laid by spawning horseshoe crabs each spring are the primary, exquisitely-timed food source for shorebirds on their northward migration through the Bay. The proposed “threatened” status for rufa red knots under the Endangered Species Act is just the latest effort by environmental activists and many biologists to restrict the horseshoe crab harvests on behalf of the birds.

Geolocators have enriched the story, but have perhaps not yet added clarity. What will knowing the previously only guessed-at migratory paths of the few, recovered red knots mean for conservation, particularly as it relates to more precise understanding of populations, stopovers, and “critical habitat” for a threatened subspecies? For that matter, what if anything can these data-loggers add to debate over the livelihoods of horseshoe crab fishers and biotech workers, or to concerns about offshore energy sources on the Atlantic coast? As is so often the case in environmental controversy, questions about the quantity and quality of data, and their utility in public dialogue, defy easy answers.

In the meantime, the shorebird teams continue to piece together migration and population details in concert with their technology-equipped research subjects. The doubts about releasing, and hoping to re-find, red knots with data-loggers mirror the larger anxieties of watching flocks come and go from the Bay more generally.

I recall standing at Mispillion Harbor, Delaware, with members of the British Trust for Ornithology in late May 2009. It was around 7:30 in the evening, dusk, and we were watching a flock of shorebirds depart for their northern nesting grounds. An incredible phenomenon, but one tinged with uncertainty. This year's cohort of rufa red knots, presumably Y0U among them, have already departed the Bay and are nesting in the Canadian arctic. The question, as cyclical as migration itself, remains: what will we find next year?