The hooded grebe (Podiceps gallardoi), discovered in 1974, has experienced a precipitous decline over the past 40 years, prompting its status to be revised from species of least concern to endangered. Little is known about the reproductive biology of the species, and this study proposed to locate and follow nesting colonies in southern Argentina; determine factors that affect breeding success; determine the highest concentration areas for the species; investigate current and potential threats to the population; and provide outreach to communities near the breeding sites to develop conservation awareness regarding the grebes.
The research team surveyed 11 mesa plateaus in southwestern Argentina, covering the entire known breeding range of the hooded grebe. This area included 181 lakes and 51 dry lakebeds. During the non-breeding season, they also surveyed six Argentine estuaries and two locales in Chile where the grebes have been previously sighted. A total of 535 adult individuals were observed in only 14 of the 181 lakes surveyed. Compared to 405 juveniles observed in a 1984 survey, none were seen in this study. Only three lakes appeared to have breeding activity, 226 nests were found, and only 28 chicks (12%) successfully hatched. In 28 lakes where individuals were observed in the 1984 survey, there were no grebes. At the wintering estuaries, grebes were present at only two sites with a total of 750 individuals sighted, likely comprising a high percentage of the total population. In comparison to the last exhaustive survey in 1984, these data suggest an 81% decline of the population overall.
While two seasons of data are not sufficient to definitively identify the causes of population decline, the researchers gathered data on predation by kelp gulls and the introduced rainbow trout (which can easily prey on adult birds). They also identified a previously unreported threat, predation by the introduced American mink. In February 2011, they witnessed the recent aftermath of a mink predation event in which 33 individuals were killed in a colony of 21 nests, of which none of the chicks survived. Surveys also documented the presence of other waterfowl, which can often be seen in the thousands at major lakes, potentially disturbing and competing with the grebes during the sensitive breeding season. The researchers are also exploring potential anthropogenic factors. Overgrazing by sheep has led to desertification on the plateaus. While this has caused the abandonment of many ranches in recent years, the physiochemical and ecological effects of this dynamic on the plateau lakes and their wildlife is unclear. Meanwhile, bycatch in estuarine net fisheries has been suggested as a threat; however, the researchers did not observe any bycatch in their surveys nor did they find any anecdotal evidence to support this as a major threat. Finally, environmental factors were considered, including drought and windstorms. While others have argued that the grebes are well-adapted to high wind environments, the researchers surveys revealed that in the 2010/11 breeding season, 90 (of the 237 total) nests were destroyed by a windstorm of over 110 km/hr that lasted 24 hours. Additional data are necessary in order to determine how to prevent further population declines.
The researchers created pamphlets and gave numerous talks to local communities and environmental organizations, provided radio and television interviews, and received attention in the print media to raise awareness about the plight of the hooded grebe. ($6,500)