Julieta Pedrana

Factors influencing guanaco distribution in southern Argentine Patagonia and implications for its sustainable use

The Guanaco (Lama guanicoe) has suffered a progressive decline in numbers because of unregulated hunting and poaching by an assumed competition with sheep. Inadequate livestock management, including keeping sheep numbers above carrying capacity, has led to a degradation of the Patagonian steppe. Recently, interest has grown towards a reduction in sheep density and diversification of extractive activities. Guanaco populations could be potentially amenable to a number of sustainable uses. Our aim was to investigate the factors that determine guanaco distribution in southern Argentine Patagonia and to generate a predictive cartography at the regional scale. We hypothesized that guanaco distribution could be determined by primary productivity, terrain ruggedness, human disturbance and poaching, and competition with livestock. Guanaco surveys were performed from vehicles using a road survey method. To analyze the relationship between guanaco occurrence and potential predictors we built Generalized Additive Models (GAMs) using a binomial error and a logistic link. We found that guanaco occurrence increased in the less productive and remote areas, far from cities and oil camps, and decreased in regions with high sheep density. These results suggest that guanacos tend to occur where human pressure is lower. One way to promote guanaco conservation would be to highlight the economic value of guanacos under the regulations imposed by a sustainable exploitation of their populations. The predictive models developed here could be a useful tool for the implementation of conservation and management programs at the regional scale.

Post-Fledging Dispersal of King Penguins (Aptenodytes patagonicus) from Two Breeding Sites in the South Atlantic

Most studies concerning the foraging ecology of marine vertebrates are limited to breeding adults, although other life history stages might comprise half the total population. For penguins, little is known about juvenile dispersal, a period when individuals may be susceptible to increased mortality given their naïve foraging behaviour. Therefore, we used satellite telemetry to study king penguin fledglings (n = 18) from two sites in the Southwest Atlantic in December 2007. The two sites differed with respect to climate and proximity to the Antarctic Polar Front (APF), a key oceanographic feature generally thought to be important for king penguin foraging success. Accordingly, birds from both sites foraged predominantly in the vicinity of the APF. Eight king penguins were tracked for periods greater than 120 days; seven of these (three from the Falkland Islands and four from South Georgia) migrated into the Pacific. Only one bird from the Falkland Islands moved into the Indian Ocean, visiting the northern limit of the winter pack-ice. Three others from the Falkland Islands migrated to the eastern coast of Tierra del Fuego before travelling south. Derived tracking parameters describing their migratory behaviour showed no significant differences between sites. Nevertheless, generalized linear habitat modelling revealed that juveniles from the Falkland Islands spent more time in comparatively shallow waters with low sea surface temperature, sea surface height and chlorophyll variability. Birds from South Georgia spent more time in deeper waters with low sea surface temperature and sea surface height, but high concentrations of chlorophyll. Our results indicate that inexperienced king penguins, irrespective of the location of their natal site in relation to the position of the APF, develop their foraging skills progressively over time, including specific adaptations to the environment around their prospective breeding site.

Guanaco abundance and monitoring in Southern Patagonia: distance sampling reveals substantially greater numbers than previously reported

BackgroundGuanacos (Lama guanicoe) are thought to have declined in Patagonia mainly as a result of hunting and sheep ranching. Currently accepted estimates of total population size are extrapolated from densities obtained through strip transects in local studies. We used road surveys (8,141 km) and distance sampling to estimate guanaco density and population size over major environmental gradients of Santa Cruz, a large region in southern Patagonia. We also calculated the survey effort required to detect population trends in Santa Cruz.ResultsWe found considerable spatial variation in density (1.1 to 7.4 ind/km2), with a mean value of 4.8 ind/km2, which is more than twice the mean value guessed for central and northern Patagonia. Consequently, guanaco numbers in Santa Cruz were estimated at 1.1 million individuals (95% CI 0.7 to 1.6), which almost doubles current estimates of guanaco population size in South America. High guanaco abundance was found in arid lands, overgrazed and unable to support profitable sheep stocks. Detecting a 50% change in guanaco population size over a 10-year period requires substantial monitoring effort: the annual survey of between 40 and 80 30-km transects, which becomes up to 120 transects if trends are to be detected over 5 years.ConclusionsRegional patterns in guanaco density can only be detected through large-scale surveys. Coupling these surveys with distance sampling techniques produce robust estimates of density and its variation. Figures so obtained improve currently available estimates of guanaco population size across its geographic range, which seem to be extrapolated from strip counts over small areas. In arid lands degraded by sheep overgrazing, sustainable use of guanaco populations would help harmonize guanaco conservation, socio-economic progress of rural areas, and eventually the restoration of shrub-steppes.

Environmental factors influencing the distribution of the Lesser Rhea (Rhea pennata pennata) in southern Patagonia

Abstract The Lesser Rhea (Rhea pennata pennata) has suffered a marked decline in numbers over recent decades, probably mainly as a result of livestock production and overhunting. Our aim was to investigate the factors that determine the distribution of Lesser Rheas in southern Patagonia and to generate a predictive regional distribution map. We surveyed 8000 km of roads and sighted 795 Lesser Rhea individuals or flocks. We also estimated environmental predictors from remotely sensed data and analysed the occurrence of Lesser Rheas in relation to these predictors. The predictors we examined were associated with four hypotheses explaining the distribution of Lesser Rheas: the persecution by ranchers, primary productivity, topography, and anthropogenic disturbance hypotheses. We built models for each hypothesis. Our results suggest that the distribution of Lesser Rheas is not negatively affected by persecution by ranchers, as the species is more abundant in areas with high stocking levels of sheep, but is positively influenced by primary productivity and negatively by the proximity of human habitation. The resulting distribution map can be used as a management tool for government agencies and highlights the conservation priorities for managing this declining and emblematic species.

Winter Population Size Estimations of Three Migratory Sheldgeese in the Southern Pampas, Argentina

Abstract. Sheldgeese [Upland Goose (Chloephaga picta picta), Ashy-headed Goose (C. poliocephala) and Ruddyheaded Goose (C. rubidiceps)] have similar migratory patterns, breeding in Patagonia (Argentina and Chile) and wintering mainly in the southern Pampas, Argentina. All of them are species of conservation concern in Argentina. The objective of this study was to estimate species densities using distance sampling and to calculate population sizes over three categories of habitat quality in the southeast of Buenos Aires Province, Argentina. Road surveys (9,200 km) were performed from a vehicle during two consecutive wintering seasons (13 June to 6 July 2011 and 9 June to 4 July 2012). Predicted probabilities of sheldgeese occurrence were divided into three classes of habitat quality. Upland Goose mean density was estimated at 3.72 individuals/km2, Ashy-headed Goose at 1.62 individuals/km2 and Ruddy-headed Goose at 0.04 individuals/km2. Consequently, Upland Goose numbers were estimated at 348,255 individuals, Ashy-headed Goose at 151,803 individuals and Ruddy-headed Goose at 498 individuals in the southeast of Buenos Aires Province. The results confirm former studies regarding the small population sizes of these species in comparison with historic data and suggest a decline in sheldgeese populations.

Niche Overlap Determination Through Habitat Suitability Models: A Management Tool for Native Birds of the Argentinean Pampas

Summary. In Argentina, predominantly in the Pampas ecoregion, the natural rangelands have increasingly been replaced by crops. Avifaunal studies have shown that the population density of several species decreased as the proportion of cropland in the landscape increased. The Greater Rhea Rhea americana and two migratory sheldgeese: the Upland Goose Chloephaga picta and Ashy-headed Goose Chloephaga poliocephala, are medium-large native species that have been common and sympatric inhabitants of the Pampas ecoregion. We aimed to analyse and compare the current ecological niches occupied by the three species during the non-breeding season in the southern Pampas of Argentina, the region where their original distributions overlapped, using Ecological Niche Factor Analysis. The three species showed high global marginality values, indicating that they occupied only a specific subset of environmental conditions of those available across the region. Suitable areas for Greater Rhea were located in the west and south of the study area, overlapping grazing lands and native habitats. The three species responded to landscape composition and configuration, as indicated by the low proportion of areas with suitable conditions for these medium-large birds. Suitable areas for Ashyheaded and Upland Geese were especially concentrated in the eastern part of the area and suitable areas for Upland Goose were more widespread than those suitable for the Ashy-headed Goose. We provide compelling evidence of low overlap between the ecological niches of the three species in the southern Pampas, which highlights the need for specific management strategies to ensure the conservation of these emblematic species. —Pedrana, J., Bernad, L., Maceira, N.O. & Isacch, J.P. (2018). Niche overlap determination through habitat suitability models: a management tool for native birds of the Argentinean Pampas. Ardeola, 65: 25–40.