GPS monitoring expertise permits scientists to fly with curlews on their epic migrations | Smithsonian voices

Paula Cimprich, Smithsonian’s National Zoo and Conservation Biology Institute

How do you study a species that travels thousands of kilometers using a mode of transport that is difficult or impossible for humans? Such is the tricky reality of studying migratory birds, whose incredible journeys take place far above the ground. Fortunately, modern technology helps us to learn more about the phenomenon of their migration.

The same weather radars we use to make weekly forecasts and track storms can also detect flocks of flying birds. We can learn about the movements of entire populations across continents and even begin to predict bird migrations. GPS trackers give us a more detailed look at individual birds wherever they travel (even across oceans). With these tools we can learn how many birds are migrating and when, what routes they are taking and where they are stopping along the way.

We can even learn how a bird’s speed, height and body orientation change in flight. We call this “flight behavior”. We’re already finding that many birds fly farther, faster, and higher than we thought. And when we consider that flight behavior tells us the relationship between birds and their aerial habitats, we can begin to unravel the mysteries of how birds achieve their amazing flights.

In 2019, researchers at the Smithsonian Migratory Bird Center began a project with the Intermountain Bird Observatory at Boise State University, American Prairie, and the University of Oklahoma Aeroecology Group to study and conserve long-billed curlews. Curlews are an iconic bird species of the Central Great Plains. The population we studied nests in north-central Montana but migrates through the Great Plains and winters south of the US-Mexico border in coastal lagoons and the high desert.

ABOVE: The long-beaked curlews we are studying nest in north-central Montana.

GPS tags are our window into the lives of these birds, helping us to understand their needs and the challenges they face at each stage of their life cycle. Attaching a GPS tag to a wild bird gives us access to incredible information that can help conserve entire populations. We use tiny markers and our protocols are designed to maximize safety and minimize stress for the birds. We understand that tagging can still cause some small disruptions to these endurance athletes, so we’re trying to squeeze every last drop of information out of tagging to achieve maximum conservation benefit for curlews everywhere.

At the start of the project, we tagged seven long-beaked curlews. The tags collect GPS points with the high accuracy your phone has when you use it to navigate while driving. We tagged 20 more birds the following year and another eight in 2021. These tags are some of the most advanced and lightweight tags available. They transmit over the cellular network, allowing us to access data in real time.

In addition to a bird’s latitude, longitude, and altitude, the tags collect flight behavior data. They’re equipped with triaxial accelerometers, tools that measure acceleration and help us identify types of movement — like flying, foraging, or resting. We’ll use all of this data to create a 3D point where a curlew was in the air. Combined with atmospheric data such as temperature, wind and barometric pressure, we get a picture of how curlews respond to changing conditions when flying. For example, a curlew may change altitude or adjust course.

A curlew carries a GPS tracking tag securely attached to its back.

Paula Cimprich, Smithsonian’s National Zoo and Conservation Biology Institute

Next, we can start asking (and answering) key scientific questions such as: B. which weather conditions could explain the flight behavior such as changes in flight altitude. And how much do birds depend on favorable winds during migration? (Think of how you’ll gain speed if you’re moving in the same direction as the wind – same goes for birds!). With climate change, these questions have a new urgency.

Climate change is making spring come earlier. It is also expected to alter atmospheric conditions such as the strength of the winds. So what could this mean for birds? If birds travel sooner or faster to keep up with the advancing spring, will they have the same wind support they evolved to use to complete their journeys? If not, will they use more energy? And how might that affect them once they reach their goal?

We can also think about ways to conserve the habitat of migratory birds in the air, just like we protect their habitat on land. Where should we create safe skies free of drones and airplanes? How can we prevent light, chemical and noise pollution in areas where birds roam? Where should we avoid building wind turbines and radio towers?

Answering these big questions will require more time and data, but the autumn 2020 migration of the long-beaked curlew is already full of interesting results. The curlews typically started long flights in the evening and often continued flying into the daylight hours. Their entire journeys took about 45 hours, with each long leg lasting 10 to 25 hours. A female curlew named Tapes flew all the way from Montana to central Mexico in a 44-hour flight, covering 1,641 miles (2,641 kilometers).

During the first part of an evening flight early in the migration, a female curlew named Carmen flew at high altitudes. She returned to high altitudes again during the daylight hours as she continued her journey south. Carmen also had the fastest ground speeds when flying at higher altitudes, suggesting that she may have found favorable tailwinds there.

The flight altitudes and speeds of the Curlew Carmen are shown graphically here. She had the fastest ground speeds when flying at higher altitudes.

Paula Cimprich, Smithsonian’s National Zoo and Conservation Biology Institute

It is exciting to analyze such data. They reveal details about the lives of curlews that would otherwise remain secret as the birds travel to and from their far-flung destinations. We still have a lot to learn. But with their high-tech tracking tags, the curlews will no doubt teach us more about how they use their important aerial habitats.

Ecology GPS tracking migratory bird research