Sheldgeese are birds endemic to South America, and three species – the ruddy-headed goose, the ashy-headed goose and the upland goose – have declined dramatically in the past century. Although population decline is attributed to many diverse factors such as hunting, modification of nesting habitat and the introduction of invasive species, the intensity of these pressures has not been evaluated. This project studied aspects of the ecology, reproductive biology and threats to these three species on the Magellanic steppe of Tierra del Fuego and Santa Cruz Provinces to develop management recommendations that support goose breeding cycles.
To measure variation in habitat use and abundance throughout the breeding and winter seasons, researchers conducted eight population surveys between 2013-2015 (three during each breeding season and one during each winter season). The number of sheldgeese varied between surveys, with the most geese observed at the end of the breeding season (fall). The largest groups were found in wetlands, on low vegetation (less than 40 centimeters) and associated with livestock. The maximum number of sheldgeese recorded was 49 in Tierra del Fuego and 16 in Santa Cruz. No individuals were found in the survey areas during the winter. For the upland goose (C. picta), breeding pairs were more abundant at the beginning of the breeding season, and represented a higher proportion of the overall population in Santa Cruz than in Tierra del Fuego (0.15 and 0.11 breeding pairs/total individuals), where breeding events were rare (Tierra del Fuego: 1/202km; Santa Cruz: 1/6km). Pairs were normally found on grass and shrub mats with taller vegetation (over 40 centimeters), near small lagoons and at sites with few livestock.
To study relative abundance and the impact of predators (native and introduced) on breeding, researchers monitored natural and artificial nests with camera traps and conducted transect surveys of carnivore sign. The grey fox Pseudalopex griseus was the primary predator of nests, responsible for 75% of predation on artificial nests in Tierra del Fuego. Natural nests were also preyed upon, primarily by domestic dogs and kelp gulls (Larus dominicanus). Carnivore sign was found in 69% of transects; of those, 100% contained sign from grey fox, 21% from mink and 3% from dog.
This information on important sites and predator species, along with data still being analyzed, are critical for defining science-based conservation action. In particular, we recommend control measures for introduced predators in important breeding areas for sheldgeese species. ($7,700)