Skip to content
Home » Projects » Assessing the importance of natural and human factors affecting the distribution of the lesser rhea and upland goose

Assessing the importance of natural and human factors affecting the distribution of the lesser rhea and upland goose

The lesser rhea (Pterocnemia pennata pennata) is distributed across wide expanses of Argentina’s sparsely populated regions. However, their populations have been in decline with hypothesized causes including environmental factors such as food competition with greater rheas and livestock, as well as direct human impacts such as hunting and egg poaching. The upland goose (Chloephaga picta) inhabits similar regions but feeds on agricultural crops and is considered by the government to be an agricultural pest, subjecting the species to hunting year-round without limits to sex, age or quantity. The goose subspecies is endemic to South America and it is likely that this unbalanced management strategy will lead to significant declines and possibly extinction.

This project supported Argentine graduate student Pedrana to train with a leading population ecology modeler in Switzerland to develop models and analyze data collected in the field in Argentina. Field data were collected by surveying the terrain and determining rhea and goose presence or absence and assessing a suite of natural variables (such as vegetation density, length of growing season and distance to nearest stream) and human variables (such as distances to nearest road, ranch and oil development). The models developed tested the ability of only natural factors, only human factors and a combination of natural and human factors to predict the presence of both bird species.

Pedrana found that the combined natural-human models were significantly better at predicting lesser rhea presence than either natural-only or human-only models. Of the individual variables, however, human factors had the highest predictive power. In contrast, for the upland goose, combined and natural-only models were much more accurate predictors of presence than human-only models. These results suggest that the rhea may be significantly more impacted by human activities than upland geese and may therefore be a higher conservation priority. However, many of these variables have complex relationships and “natural” effects in this study may in fact be indirect effects of human activities (such as changes in vegetation due to livestock or agricultural development), so additional research will be required in order to fully understand the population dynamics and conservation needs of these species.

See the publication Primary productivity and anthropogenic disturbance as determinants of Upland Goose Chloephaga picta distribution in southern Patagonia.