Silvia Puig

Habitat use by guanacos (Lama guanicoe, Camelidae) in northern Patagonia (Mendoza, Argentina)

Strategies of habitat use of the guanaco were analyzed in early and late summer, when parturition and lactation increase nutritional needs and predation risk. The daily distribution of guanacos was followed by scan‐sampling, relief and soil were measured in each habitat, and vegetation was analyzed by the point‐quadrat method. Guanacos showed a selective habitat use, preferring open areas with grasslands, gentle terrain and low hiding cover. The density of guanacos was positively associated with the intensively eaten grass Panicum urvilleanum, and negatively associated with rocky soils, high shrublands and avoided plants. A weakening of the selective habitat use occurred when the abundance of guanacos increased in the study area during late summer, ceasing avoidance of poor and risky habitats.

Diet Selection by the Fossorial Rodent Ctenomys mendocinus Inhabiting an Environment with Low Food Availability (Mendoza, Argentina)

The seasonal diet of Ctenomys mendocinus was determined in a habitat of the Andean Precordillera, through microhistological analyses of stomach contents and in relation to food availability. Diet included 23 genera of plants and only 6 of them were consumed with frequencies higher than 4%. The grasses Stipa and Elymus comprised about 80% of the diet. A high proportion of aerial plant material was registered throughout the year suggesting a tendency to forage on the surface. Dietary selectivity was evidenced by a preferential consumption of grasses and avoidance of shrubs. Moreover, most dietary items frequently used were eaten in proportions that differed from their availabilities. This non-opportunistic feeding behavior, specialized in a few dietary items, did not agree with the one expected for a subterranean rodent inhabiting an environment with severe climatic conditions, low food availability and patchy distribution of food resources.

Diet of the Lesser Rhea (Pterocnemia pennata) and availability of food in the Andean Precordillera (Mendoza, Argentina)

Abstract The food and foraging strategies of the Lesser Rhea (Pterocnemia pennata) were studied in the high arid pampas of the Andean Precordillera in Mendoza, Argentina. The Lesser Rhea is primarily herbivorous and the composition of, and seasonal changes in, the diet were analysed in relation to the availability of vegetation. The analysis of vegetation and sampling of faeces were carried out in spring, summer and autumn 2002–03. Grasses and shrubs dominated the vegetation of the study area, while forbs and cactus (Cactaceae) were present only in low proportions. The main dietary component was leaf matter (94.30%), with the rest seeds (5.66%) and a small proportion of insects (0.03%). Stones constituted 2.24% of the dry weight of faeces. The diet included 70% of the available plant species in the area. Rheas showed a preference for forbs and shrubs in relation to the availability of these plant-types and, while grasses were the dominant plant-type in the environment, they were not selected in relation to their availability; Rheas showed no preference for cactuses. Dietary diversity (Shannon-Wiener index of diversity of plant species in the diet = 0.77) exceeded environmental diversity (Shannon-Wiener index = 0.29). The diet of the Lesser Rhea in the Andean Precordillera of Mendoza was almost completely herbivorous and generalist, although selective for some plant species, features that would constitute an adaptation to survive in this clearly arid environment.

Vigilance behaviour of the year-round territorial vicuña (Vicugna vicugna) outside the breeding season: Influence of group size, social factors and distance to a water source

We conducted focal observations of vicuña, a year-around territorial mammal, to compare vigilance behaviour between territorial and bachelor males outside the reproductive season. We hypothesized that the time spent vigilant would depend on male social status, considering the potential effects of several variables: sampling year, group size, distances to the nearest neighbour and to a vega (mountain wetland). We fit GLM models to assess how these variables, and their interactions, affected time allocation of territorial and bachelor males. We found non significant differences between territorial and bachelor males in the time devoted to vigilance behaviour. Vigilance of territorial males was influenced by the sampling year and the distance to the vega. In turn, vigilance in bachelor males was influenced mainly by the sampling year, the group size and the distance to the vega. Our results suggest that sampling year and distance to the vega are more important than social factors in conditioning the behaviour of male vicuñas, during the non-reproductive season. Future studies of behaviour in water-dependant ungulates, should consider the influence of water and forage availabilities, and the interactions between group size and other variables.

Environmental factors affecting the distribution of three armadillo species (Xenarthra, Dasypodidae) in Argentina

Abstract Environmental temperature, rainfall, vegetation structure, soil composition and land use were recognized as relevant factors limiting the distribution of armadillos. The aim of this study was to identify environmental and spatial factors influencing the geographical distribution of the most widespread armadillos occurring in Argentina (Chaetophractus vellerosus, Chaetophractus villosus and Zaedyus pichiy), through the most simple and accurate explanatory modeling. General linear models (GLMs), partitioning analyses of variance and hierarchical partitioning analyses were applied to estimate the species-environment relationships. Climatic variables were recognized as the most relevant factors influencing the three species distribution, consistent with that expected from the hierarchical structure theory in ecological systems. Optimal conditions were mainly arranged in a longitudinal geographic gradient for Chaetophractus species and in a latitudinal-longitudinal gradient for Z. pichiy. The optimal habitat identified for C. vellerosus, larger than previously documented, was characterized by warm, rainy summers and moderately cold, dry winters. The distribution of C. villosus was mainly influenced by temperate conditions of temperature and isothermality, scarcity of rainfall with high seasonality and low aridity conditions, and prevalence of sandy soils. Optimal habitat of Z. pichiy was affected by low temperatures with high seasonality, scarcity of rainfall with aridity conditions and sandy soils.

Diet of brown hare (Lepus europaeus) and food availability in High Andean mountains (Mendoza, Argentina)

Abstract Diet selection by Lepus europaeus was studied in high-altitude mountain environments with severe weather, presence of wetlands, and no agricultural activities. Diet was assessed using fecal microhistological analysis, and food availability by point-quadrat transects in four habitats, two of them with wetlands. Significant differences were determined with Kruskal-Wallis ANOVA, similarities by Renkonen index, and feeding selection by χ2-test and Bailey’s confidence interval. The diet included 63% of all species present. Shrubs dominated the diet. Food use was opportunistic in habitats without wetlands, where grasses and shrubs were more available. Plant cover and availability of grass-like plants were higher in wetland habitats, where shrubs and forbs were preferred and grass-like plants were avoided. Similarity between diet and food availability was higher on dry soils, dominated by grasses and shrubs, than in wetland microhabitats with higher plant cover, diversity, and percentage of grass-like plants. Dietary generalism was confirmed, especially when excluding wetland vegetation. Hard Juncaceae cushions accounted for the pronounced selectivity in habitats with wetlands. Dry soils, where shrub patches provided good food and shelter, appear as major feeding microhabitats for L. europaeus. Spatial heterogeneity protection, at landscape and microhabitat scales, is relevant to the brown hare conservation in High Andean environments.

Dietary overlap of coexisting exotic brown hare (Lepus europaeus) and endemic mara (Dolichotis patagonum) in Northern Patagonia (Mendoza, Argentina)

Abstract Introduced brown hares are present across the distribution range of maras, which are endemic to Argentina’s open steppes. Food competition with exotic herbivores could be partially responsible for declines in mara populations. Diets of sympatric hares and maras were compared to detect dietary overlap according to food availability. Diets and availability were estimated using microhistological analysis and point-quadrat transects, over four seasons. Horn’s index estimated dietary overlap, Kruskal-Wallis ANOVA detected significant differences, and permutational multivariate analysis of variance (PerMANOVA) determined the multivariate response to factors. Grasses prevailed among available items and in both diets. Plant cover and richness increased in summer and forbs in spring. High dietary overlap decreased in autumn-winter, when hares ate more forbs and tall shrubs and less low shrubs than maras. Interspecific overlap was higher inside a protected area with higher food diversity, more forbs, and low shrubs. Both herbivores shifted to different foods as availability decreased. When forbs declined, they were less eaten by maras than hares. Broader habitat use allows hares to search for preferred forbs farther away than maras. The more adaptive hare could become a stronger competitor in impacted environments. Better food availability inside than outside the protected area is a feeding advantage for the coexistence of these herbivores.