Cholao and what satellite tracking reveals about its incredible migratory route across the Americas

Cholao, a small Lesser Yellowlegs (Tringa flavipes) is becoming a well-known character among Audubon's social media followers. Its migratory journey between the Cauca Valley, in southwestern Colombia, and the boreal forests of Canada, is monitored with a satellite GPS transmitter that tracks its whereabouts, its movement, its epic crossing over the Gulf of Mexico until touching down in Louisiana, and its flight to the boreal forests of Canada.

Jorge Velásquez, Audubon's Science Director for Latin America and the Caribbean, is perhaps the one who knows the most about the life and travels of Cholao —who is not just one, but several individuals— as he has spent several years tracking not only this specific bird, but the flights of 34 other "tringas," as they are informally called. With his help, we answer some of the frequently asked questions about this bird and its impressive journey.

How did the tracking of these migratory birds get started, and why focus on the Lesser Yellowlegs rather than another species?

We began tracking the movements of Tringa flavipes in the Cauca Valley, Colombia, in April 2022. Two factors influenced this choice: first, it is one of the shorebirds whose population has declined significantly; and second, it is a species associated with two crops closely tied to our work in the Cauca Valley — sugar cane and rice. This sparked our interest in learning more about how long these birds remain in the region during the wintering months, their migratory journeys, their origin, and their nesting areas in the boreal forests.

Have you always used the same tracking technology, or has it changed over the years?

It has changed! We started with Motus transmitters, even though there were no Motus stations in the Cauca Valley that could detect them. Tracking the movements of these tringas was not just a matter of fitting them with radio transmitters, but also establishing the infrastructure in the region to be able to monitor them. In fact, of the first 10 tringas we captured — during an exercise we did with Selva, a Colombian research and conservation organization — we never knew when they left the country, because there were no stations.

Motus has been the technology in which we have invested the most time and resources to track the tringas. But it has a major limitation: it requires network coverage, which is very good in the United States and in certain countries in Latin America. But once the birds cross the border into Canada, especially in the central part of the continent, Motus coverage is very poor.

Does that mean we don't know what happens to them?

In the first two years of tracking the 30 individuals we had tagged, we would lose track of them once they passed through North Dakota. That is why, in 2025, we started using satellite transmitters, which give us a better record of local movements. This way, we have already identified the area where they are possibly nesting — and we are now trying to verify it in person.

Do these birds follow the same migration route each year, both on their way north and on their return to the Cauca Valley? How predictable are Lesser Yellowlegs?

I do think there are some patterns in their routes. We have seen that, in general, during the spring migration, in the months of April and May, birds seem to be in a race to reach their nesting grounds in the boreal region of North America. The most efficient route for that purpose is the Midcontinent Flyway — practically a straight line through all the central states of the United States until crossing the border into Canada.

In the fall migration, there is more variability: some go through the central states and make stops along the way, probably gathering food and energy. Others take interesting detours: we have had tringas that enter through Minnesota and North Dakota, while others go all the way to New York and come down the East Coast. There are also tringas that come down through the middle of the country and end up in Kentucky, Tennessee, South Carolina, and leave through Florida. And still others come down the same route we have detected them using during the spring migration.

In Cholao's recent journey, the route looks very much like a straight line — efficient.

That is what we observed with Cholao, tagged with GPS: it made practically an uninterrupted two-and-a-half-day journey between Cali and the Louisiana coast. As soon as it arrived in Louisiana, Cholao spent a week there — I imagine recovering from the trip, feeding, and gathering energy. From there it flew to Iowa, where it stopped at a large swamp, surely full of food at this time of year. And from there it flew to its current area in the province of Saskatchewan, Canada.

Another quick fact about Cholao: how fast does it fly?

Based on what we have recorded, at least during its ocean crossing and depending on factors such as wind and weather, they average 25 to 30 miles per hour (45 to 50 kilometers per hour).

How is this data useful to us, and how does it inform decision-making?

Tracking the movements of tringas and other birds allows us to identify the stopover sites of migratory birds — in other words, their "hotels and restaurants." For this, the Motus network is very useful, since having data from 30 or more tagged individuals allows us to identify the most heavily used areas, and thus get a better idea of the threats they face along their migration route. As an organization dedicated to bird conservation, this allows us to begin managing actions to address those threats.

And at a more local scale — for which satellite transmitters are very useful — we can pinpoint exactly which land plots the tringas use, visit them, and investigate what they do there, their environmental characteristics, and what may affect them. With just five individuals tagged with GPS, we already have almost 30,000 detections — an impressive amount of data that can support decision-making at a very detailed scale.

What is the equipment the bird carries like? Does it make it significantly heavier or more vulnerable to predators or potential mates during the reproductive stage?

For both Motus transmitters and those that use satellite positioning, the type of transmitter is the same: a tiny backpack worn on the bird's back, where only the shape and weight vary slightly. The Motus transmitter is a bit flatter and lighter, weighing less than two grams, while satellite ones weigh around two grams.

Regarding the effect on individual birds, there is always a concern that they may impact mortality — not so much because they make them more attractive as prey, but because the harness can limit mobility if it is not fitted correctly. That is why only certified personnel handle the installation.

The other factor is that migration carries an energy cost, and those two grams can make a big difference. In most species studied for migration, the aim is to keep transmitter weight below three percent of the individual's body weight. Until a few years ago, it was impossible to think of putting satellite transmitters on a bird like Cholao — on a tringa — because they were all too large. Now we can have transmitters below three percent, which gives us some peace of mind regarding the survival of the tringas. In any case, it must be evaluated with data whether fitting the transmitters is having an effect on survival.

And what is the lifespan of these transmitters? How do they work?

Both types of transmitters, GPS and Motus, use sunlight to produce power. In the case of the Motus transmitters, they have a battery that recharges with sunlight — as do the satellite ones — and in theory they can last several years. However, the longest we have managed to track a single individual is two years. It is believed that this happens due to wear and tear of the harness, which is made of nylon and falls off.

With the data collected so far, what has surprised you?

I was expecting a stronger association between the tringas and natural habitats or wetlands. I imagined that in the Cauca Valley there would be a concentration around Laguna de Sonso or the Cauca River. But no! The association of the Lesser Yellowlegs with rice crops is incredible — practically wherever there is a rice crop, they are there or will arrive.

This means we are on the right track, and we must focus on implementing bird-friendly practices in the Cauca Valley, where these rice crops are a key piece of the migratory puzzle.