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

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A species distribution may be determined by its responses to patterns of human distur-bance as well as by its habitat preferences. Here we investigate the distribution of theUpland Goose Chloephaga picta, which has been historically persecuted by farmers andranchers in Patagonia because it feeds on crops and pastures and is assumed to competewith sheep for forage. We assess whether its current breeding distribution is shaped bypersecution by ranchers or whether it can be better explained by differences in habitatprimary productivity and preference for wetlands, or by other anthropogenic distur-bances not associated with ranching. We built species distribution models to examine therelative effect of environmental and anthropogenic predictors on the regional distributionof Upland Goose. We performed vehicle surveys in the province of Santa Cruz, Argen-tina, in two years, surveying 8000 km of roads and recording 6492 Geese. Generalizedadditive models were used to model the presence⁄absence of Geese in 1-km cells. Themodels suggested that Upland Goose distribution is not currently affected by ranchercontrol, as the species is more abundant in areas with high sheep stocking levels, but it ispositively influenced by primary productivity and negatively influenced by urban areas.Anthropogenic disturbance caused by urban areas and oil extraction camps had a greaterimpact in limiting the species distribution than sheep ranching.Keywords: human disturbance, large-scale habitat models, primary productivity, semi-arid steppe,species distribution models, wildlife–livestock conflicts.Anthropogenic impacts are a major factor in deter-mining bird distributions and population trends(Newton 2004, Coombes et al. 2008, Moller2008). Disturbance can take many forms, forexample direct impacts such as habitat alteration,hunting or persecution (Brawn et al. 2001, Thiollay2006), and others of a more indirect nature, suchas additive reactions to human recreational activi-ties (Gill 2007, Kerbiriou et al. 2009). The currentgeographical ranges of many bird species mayreflect not only their habitat preferences but alsohuman disturbance (Caughley & Gunn 1996). Inareas long inhabited by humans, the original birdcommunities may have been trimmed, and therebyreduced to a subset of relatively tolerant species(Blumstein 2006, Devictor et al. 2007). However,the early effects of human disturbance on sensitivebirds could be best detected in protected or remote,recently or scarcely populated areas (Trainor 2007,Lees & Peres 2008).There is empirical evidence that many birdsavoid human disturbance and that their populationsizes can be negatively affected, but little is knownon the real magnitude of human disturbance atthe scale of a species distribution. To estimatethe effects of human disturbance it is necessaryto model the expected distribution of thespecies based on habitat preference, quality andavailability, and then estimate the effect of human