This a continuation of a 2009 CREOi-funded project. The torrent duck (Merganetta armata armata) inhabits the rivers of the high Andes, specializing in fast-flowing waters from Venezuela to Tierra del Fuego, following the mountainous spine of the Andes. The species’ IUCN conservation status is Least Concern; however, it has been classified as threatened in Argentina and in other range countries due to documented population declines. These declines are due to human recreational activities and the introduction of invasive species, especially the American mink (Neomustela vison), which preys on torrent duck eggs, chicks and adults.
The goal of this study was to determine whether there were differences in torrent duck population dynamics between areas where mink are present and absent. Two methods were used: 1) the capture of birds with mist nets along with banding for long-term identification; and 2) the creation of a photographic catalogue of male torrent ducks. This latter tool was employed where rivers were too wide for mist nets, using the individually unique patters of head plumage to distinguish males.
A total of 33 torrent ducks were captured and banded and 20 males were photo-identified. These individuals were tracked between one and four years, and researchers determined that torrent ducks switched mates every one to two years in areas with mink, while in areas without mink only one male switched mates during the entire study period, after three years. This was of particular interest because in mink-free areas the torrent duck populations have been established for longer and there tend to be more territorial disputes. Torrent ducks in areas with mink also exhibited lower reproductive success, suggesting that mink are negatively impacting the population, though more data are required to draw firm conclusions.
While banding birds, feathers were also sampled to conduct population genetic analyses. This effort, currently in progress, will allow researchers to understand whether there is healthy gene flow between populations and, indirectly, whether torrent ducks fly only along water courses (as reported in the literature) or traverse forests and mountains. This information is critical for future management plans.
During the field work for this project, a first-of-its-kind discovery was made: torrent ducks are the first bird species to have been observed swimming in thermal waters, tolerating temperatures up to 122°F along with strong currents. This suggests unprecedented behavioral and physiological plasticity, despite the species being considered a habitat specialist.
Diverse outreach efforts included presentations to the public; production of the documentary Torrent ducks: The struggle for survival, which was shown in primary and secondary schools (available on YouTube at https://www.youtube.com/watch?v=7CamRzCRkuc); a torrent duck Facebook page (https://www.facebook.com/PatodeTorrente); and four scientific publications. ($3,520)