Somewhere over the Gulf of Mexico, a bird barely heavier than a handful of coins flew for two and a half days without stopping. No land, no rest, no food — just open water beneath it and Canada somewhere ahead.
That bird is Cholao, a Lesser Yellowlegs shorebird that began its journey in the sugarcane fields of Colombia’s Cauca Valley. Its name belongs to more than one individual, but the GPS data streaming back from its tiny transmitter is telling a story researchers have been trying to piece together for years — about a species in steep decline, and a migration far more complex than anyone expected.
A species in trouble — and a valley full of clues
The Lesser Yellowlegs (Tringa flavipes) is one of the most steeply declining shorebirds in the Americas. What drew Audubon’s Latin America team to Colombia’s Cauca Valley in April 2022 was something more specific: the bird’s unexpected relationship with agriculture.
The Cauca Valley is sugarcane country. Audubon had been working there to encourage more sustainable farming — specifically, rotating sugarcane with rice — when researchers kept noticing Lesser Yellowlegs using those crops with surprising regularity. Where were these birds coming from, and what were they facing along the way?
That question launched a multi-year tracking effort involving more than 34 individual birds. Understanding migration routes, wintering densities, and the threats birds encounter somewhere between Colombia and Canada is the foundation for any serious conservation strategy.
From radio tags to satellites: building the tracking infrastructure
Tracking a migratory shorebird sounds straightforward. It isn’t. When the team began, the Cauca Valley had no Motus radio-receiver stations at all, meaning they had to build the infrastructure before tagging a single bird.
Even after that work was done, early results were humbling. Of the first 10 birds tagged — in a joint effort with Colombian conservation organization Selva — researchers never recorded when any of them left the country. The stations simply weren’t ready in time.
Motus coverage improves considerably through the United States and parts of northern South America, but collapses in central Canada. About 30 individuals vanished from the record that way, their fates unknown. Satellite GPS transmitters changed that, transmitting continuous location data without relying on ground infrastructure. Cholao was the first to show researchers what that actually looks like.
Cholao’s journey: a 2.5-day nonstop flight across the Gulf
The GPS data from Cholao is almost hard to absorb. The bird flew from Cali, Colombia, to the Louisiana coast in approximately two and a half days — nonstop, over open water, averaging 25 to 30 miles per hour depending on wind and weather.
When it landed, Cholao stayed in roughly one location for about a week, recovering and feeding, rebuilding fat reserves burned during the crossing. Then it moved to Iowa — likely a food-rich wetland — before continuing north to Saskatchewan, Canada, its presumed nesting ground.
What makes GPS tracking different from Motus isn’t just range — it’s resolution. The data shows fine-grained local movements: exactly which fields, water bodies, and crops a bird uses, and how long it lingers in each.
Spring sprints and fall detours: what migration really looks like
Spring migration, in April and May, looks almost geometric. Birds follow the Midcontinent Flyway — a near-straight line through the central United States — as if racing a clock. Reaching boreal breeding grounds before the short northern summer closes is a matter of survival.
Fall migration is a different story. Some birds hug the East Coast; others cut through the Midwest or exit through Florida. Researchers are still working out what drives the variation.
One concern is climate-driven “false springs.” When temperatures rise early, birds may read the warmth as a signal to begin breeding cycles — only to be hit by a late frost. Whether this is already affecting Lesser Yellowlegs populations isn’t confirmed, but the possibility is real. Before any major flight, birds engage in intense feeding to build fat reserves, their only fuel over open water.
Rice fields, not wetlands: the surprising conservation lesson
Jorge Velásquez, Audubon’s Science Director for Latin America and the Caribbean, expected the birds to concentrate around natural wetlands — the Sonso Lagoon, the Cauca River. That’s not where they were. The Lesser Yellowlegs showed a strong preference for rice crops. Wherever rice was growing in the Cauca Valley, the birds followed.
That finding reshapes conservation priorities. Protecting natural wetlands still matters, but bird-friendly farming practices in rice fields may be just as critical for this species’ survival on its wintering grounds.
The growing dataset is also helping identify the stopover sites birds depend on during migration — what Velásquez calls the “restaurants and hotels” of the flyway. The solar-powered transmitters weigh just under two grams and can track a single bird for up to two years. As more individuals are tagged, the ability to coordinate conservation across every country these birds pass through will keep expanding.