Photo: Luis Javier Valbuena / WCS Colombia
By Jacobo Patiño Giraldo
River rapids can be deceptive. For those accustomed to walking on solid ground, one misstep on slippery rocks or in swirling whitewater may be enough to leave them at the mercy of the current. Yet one bird moves through these conditions with remarkable ease: the Torrent Duck.
Highly adapted to diving against fast-moving currents in search of food, the species has also become an important indicator of ecosystem health in the upper Saldaña River basin, one of the Magdalena River’s most important tributaries in Colombia’s Tolima Department.
A Bird Shaped by Water
The Torrent Duck (Merganetta armata) is a medium-sized bird measuring about 40 centimeters (16 inches) from bill to tail. Males are distinguished by their white heads marked with black stripes, while females display chestnut-colored plumage on the breast and belly and grayish heads that blend into the mottled tones of their wings.
“Its diet depends mainly on macroinvertebrates, particularly insect larvae and nymphs,” explains Lina María Caro, biologist and Sustainable Landscapes Coordinator at WCS Colombia. “These organisms live beneath rocks or in sandy areas of rivers, which is why the ducks spend so much time diving to find them.”
Torrent Ducks are also monogamous and highly territorial. Pairs remain together throughout their lives and defend their stretches of river.
“Sometimes we observe pairs with their young, and because they are so territorial, we have even seen neighboring pairs fighting each other,” Caro says. “It appears that each pair controls a section of the river, and when one enters another’s territory, conflicts begin.”
Because of their close relationship with rivers, changes in water quality can directly affect the species, particularly through the loss of macroinvertebrates, one of their primary food sources.
“Although these aquatic organisms can tolerate a certain degree of pollution, if contamination reaches very high levels, the species disappears from the area,” Caro says.
Water quality, however, is only part of the story.
“We have evaluated many variables, including natural vegetation along the riverbanks and the width of the river channel,” she adds.
This sensitivity to environmental change makes the Torrent Duck an important bioindicator. Its presence—or absence—can reveal much about the health and conservation status of aquatic ecosystems. For that reason, the Saldaña River: A Basin of Life initiative selected the species to assess whether its conservation actions are contributing to healthier rivers and surrounding landscapes.
Tracking an Elusive Species
To monitor the Torrent Duck, researchers surveyed 400-meter stretches along the Amoyá, Cucuana and Siquila river sub-basins near the municipalities of Chaparral, Roncesvalles and Planadas in Tolima.
Photo: Luis Javier Valbuena / WCS Colombia
“The idea was to include farms where conservation measures had been implemented, such as keeping cattle away from riverbanks,” explains biologist Javier Valbuena, who participated in the fieldwork. “We carried out 11 surveys in each sub-basin, for a total of 33 transects, along with repeated surveys over a five-year period.”
Tracking the species proved particularly challenging. In addition to being sensitive to environmental changes, the birds react quickly to disturbances, diving underwater or flying away at the slightest noise.
“The closest we could observe them using cameras or binoculars was between 50 and 100 meters away,” Valbuena recalls. “We had to move very carefully, wear dark clothing and avoid sudden movements.”
The bird’s elusive nature required researchers to adapt their monitoring methods.
“Two people entered the selected river section from opposite directions—one moving upstream and the other downstream—until they met in the middle,” Valbuena explains. “The idea was that if one observer startled the duck, the other would still have a chance to see it. We also looked for signs of the species, including feathers and droppings left on riverside rocks.”
Researchers also assessed environmental conditions along the transects to understand which factors might influence the bird’s presence or absence.
“We evaluated whether the water was cloudy because of rainfall, the characteristics of the riverbanks, and pressures such as cattle grazing or waste,” he adds.
Signs of a Healthy River
“Our monitoring showed that Merganetta armata occurs more frequently in places where both the water and the surrounding environment remain in good condition,” says Leonor Valenzuela, Ph.D. in Ecology and Analysis and Synthesis Coordinator at WCS Colombia.
Photo: Luis Javier Valbuena / WCS Colombia
“We combined different habitat-quality variables into a single measurement called the Visual Channel Index and found that the species is more likely to occur where this index is higher. In simple terms, higher values indicate healthier habitat conditions.”
Valenzuela explains that factors such as channel stability and water quality have helped researchers better understand why the species is present in some places and absent in others.
“In addition, we confirmed that the species is closely associated with rivers that support healthy macroinvertebrate communities, which make up a significant portion of its diet,” she says.
Researchers also observed encouraging changes within the monitored riparian ecosystems.
“In particular, we saw a gradual reduction in cattle presence and an increase in vegetation along riverbanks,” says Valbuena. “All of this contributes to improving aquatic habitat conditions.”
“These are slow processes that take time,” adds Valenzuela. “The recovery of riparian vegetation and the reduction of certain pressures help maintain river stability and preserve the habitat conditions required by the Torrent Duck.”
For researchers, these findings reinforce the value of the species as a bioindicator. Its presence depends not only on clean water, but also on healthy rivers that maintain their natural dynamics, including the aquatic communities that sustain life in these ecosystems.
Another important outcome of the monitoring has been the response of local residents. Many people had seen the bird before, but few knew much about it.
“Because it is such a beautiful bird with striking colors, people become interested in it and learn about its importance as a natural indicator of healthy ecosystems,” Valbuena says.
Nature’s balance depends on countless relationships that often go unnoticed. That is why bioindicators are so valuable. Seeing a Torrent Duck skillfully swimming against the current is not only a remarkable sight—it is also a sign that the river and its surrounding landscapes still provide the conditions necessary for life to thrive.
Saldaña River: A Basin of Life is a public-private partnership involving Fundación Grupo Argos, Concretos Argos, Colombia’s National Natural Parks, Cortolima and WCS.