Retamosa was in the midst of replacing the batteries in a tape recorder when she heard the call of a bellbird for the very first time. Standing amidst the forest canopy, she gazed upward, trying to locate the source of its striking metallic and powerful sound, searching for the bird for half an hour without success. The bellbird sings from high in the treetops, visible to its peers but hidden from those on the ground. Nonetheless, Retamosa beamed with joy: she nurtures ecosystems in Costa Rica’s AmistOsa Biological Corridor, connecting with them through her careful listening.
In the natural world, living organisms depend on sound for virtually everything. They produce calls to attract mates, communicate their identities, issue warnings, navigate, and assist in both hunting and defense. For decades, researchers have been tracking species while holding recorders, and continue to do so, though they increasingly employ remote recording technology. The analysis of the sounds produced by organisms is termed bioacoustics. Retamosa has been engaged in this field for a decade.
Through the use of bioacoustic recordings, studies have revealed that certain birds amplify their calls to be heard in urban environments, while sea turtle hatchlings communicate from their nests to time their hatching. Furthermore, when bioacoustics is combined with other sound elements—those produced by humans as well as the natural sounds of the environment, like the crashing of ocean waves—it enables a deeper ecological interpretation. This broader sound analysis is referred to as ecoacoustics, and it represents the very work taking place in Costa Rica.
For 20 years, Retamosa has operated at the National University of Costa Rica, specifically at the International Institute for Conservation and Wildlife Management. She employs bioacoustics and ecoacoustics to scrutinize the sounds of this small Central American nation, which is home to over half a million species.
“Sounds have often been overlooked in conservation efforts,” Retamosa remarks. “We tend to hear more than we see. It’s likely that any disruptions in a system could be noticed sooner through sound, or the absence of sound, compared to other indicators.”
The advancement of automated recording technology has transformed the fields of bioacoustics and ecoacoustics. Research teams can now install sensors that record snippets of audio for months on end without disturbing wildlife. Retamosa values this approach because it is non-invasive to animals, facilitating monitoring over extensive and challenging terrains, and occasionally leading to the discovery of elusive species.
While she prefers to monitor ecosystems remotely, Retamosa still has to venture deep into the forest to deploy recorders. These field trips are exhilarating but never resemble a casual Sunday stroll. She has trekked miles through mud and fallen branches, along with her colleagues Jimmy Barrantes and Randall Jiménez, traversing endless slopes. On one occasion, she fell and fractured her ribs. However, the work doesn’t conclude with installation; they must return to replace batteries and memory cards. In other regions, solar panels and internet connections enable real-time data retrieval; in the dim, humid rainforests of Costa Rica, it remains a manual task.
