Sonia C. Zapata

Analysis of trophic structure of two carnivore assemblages by means of guild identification

We evaluated the existence of trophic guild structure, considering seasonal and annual variation, in two terrestrial carnivore assemblages: one from Santa Cruz province (Argentinean Patagonia, composed by six carnivore species), and the other from Doñana National Park (SW Spain, composed by five carnivore species). To identify trophic guilds, we first studied seasonal and annual diets of predators, calculated trophic overlap among species pairs, and then constructed overlap matrices (similarity matrices). We determined guild membership objectively by entering the similarity matrices into the clustering technique unweighted pair-group method with arithmetic averaging. Carnivores from both assemblages were grouped, respectively, into four feeding guilds. Lagomorphs and rodents promoted the formation of two feeding guilds in both study sites, although the taxonomic composition of predator species that composed them was different. The ungulates-edentates feeding guild was only present at Santa Cruz, whereas the birds and reptiles feeding guild was only present at Doñana. Invertebrates and fruits were the base for the formation of a guild composed by species of the same taxonomic origin both in Santa Cruz and Doñana. Guild structure of Santa Cruz and Doñana assemblages did not exhibit seasonal or annual variation, although the specific guild composition changed over the two studied periods for both assemblages. This structure probably responded to discontinuities in resource spectra in Santa Cruz and fluctuations in rabbit abundance in Doñana. Our results support the hypothesis that establishes that guilds are originated by opportunistic convergence of species on abundant and energetically rewarding resources.

Food habits and resource partitioning between grey and culpeo foxes in southeastern Argentine Patagonia

Abstract We studied the annual and seasonal food habits of sympatric grey fox (Lycalopex griseus) and culpeo fox (Lycalopex culpaeus) in a protected area, in southeastern Argentine Patagonia, to test the hypothesis that both foxes partition prey. Grey foxes consumed a larger proportion of rodents than culpeos (66.1% versus 37. % of occurrences in feces, respectively), and culpeos consumed a larger proportion of the introduced European hare (Lepus europaeus) (32.8% versus 7.1%, respectively). Additionally, arthropods made up a significant portion of the diet of the grey fox, and occurred in the 95.5% of the analyzed feces. Despite the great differences in size of culpeo and grey foxes, the former being significantly larger, both species consumed the same type of prey, and no significant differences in the mean weight of vertebrate prey were detected in their diets. Culpeo and grey foxes diets differed during spring – summer with low values of mean diet overlap (31%). But in autumn – winter, when prey diversity is lower in Patagonia, diet was more similar and diet overlap (73%) increased. An exploratory analysis of habitat use by culpeo and grey foxes suggested that both species utilize habitat in a similar way. Our data agree with generalizations about competitive interactions between the large and the small canid in an assemblage. Although both foxes can potentially consume the same type of prey, through interference the larger culpeo would exclude the smaller grey fox from habitats with high-quality prey, resulting in prey partitioning. The possibility that both foxes partition habitat at a finer scale in our study area should be explored.

The ecological role of native and introduced species in the diet of the puma Puma concolor in southern Patagonia

There is evidence for the ecological extinction of the native prey of the puma Puma concolor in north- western Argentine Patagonia. In this study we examine whether this is also the case in southern Patagonia. From 2004 to 2007 we examined the pumas diet in three protected areas and two sheep ranches in Santa Cruz province. A total of 282 puma scats were analysed. In two of the protected areas and in the ranches 60-74% of the pumas diet was native prey. Prey species were primarily guanaco Lama guanicoe, followed by Patagonian mara Dolichotis patagonum, lesser rhea Pterocnemia pennata pennata, Patagonian pichi Zaedyus pichiy and Magellanic penguin Spheniscus magellanicus. In the third protected area the main prey was the European hare Lepus euro- paeus. Our results show a clear difference in the diet of the puma in southern compared to north-western Patagonia. Large native herbivores (i.e. guanaco and lesser rhea) maintain their role as the main prey species for the puma in southern Patagonia. We suggest, therefore, that native prey could be restored to those areas of Argentine Patagonia, such as the north-west, where they are currently ecologically extinct. Facilitating native species recovery and/or restoration and applying more rigorous controls to prevent the introduction of potential alien prey species of the puma, both within and outside protected areas, needs to be evaluated as a regional strategy.

Seasonal feeding habits of the Patagonian hog-nosed skunkConepatus humboldtii in southern Patagonia

Diet of Patagonian hog-nosed skunkConepatus humboldtii Gray, 1837 was studied in southeastern Argentinean Patagonia. Faeces from skunks were collected and analysed on a yearly basis. A wide variety of prey ranging from invertebrates (81.6% of occurrences), mammals, reptiles and plant material occurred in the faeces. Though Patagonian hog-nosed skunk was reported as primarily insectivorous regarding its feeding anatomy and behaviour, vertebrate prey predominated over invertebrates when results were expressed as consumed biomass. The consumption of invertebrate prey increased during summer, probably due to an increase in its abundance. The increase in the consumption of rodents and carrion by skunks during autumn-winter could be due to a shift from open grassy areas to other habitats to find alternative prey.

Evaluation of neophobia and its potential impact upon predator control techniques: A study on two sympatric foxes in southern Patagonia

An alternative approach to increase the efficiency of predator control and selectivity is to consider the natural behavioural repertoire of the target species and how such behaviours may increase their vulnerability. Neophobia, or the hesitancy to approach a novel food item, object, or place, is an important factor influencing the investigative behaviour of animals, and its incorporation to predator control techniques may help to reduce losses of livestock to predators. In this study, we simultaneously evaluated the existence and intensity of neophobic responses in two sympatric fox species, the Culpeo (Pseudalopex culpaeus) and the Grey (P. griseus) foxes in southern Patagonia, Argentina. For this purpose, we used bait stations to compare fox behavioural responses in the absence (pre-treatment), presence (treatment) and removal (post-treatment) of a novel stimulus, which consisted of an orange PVC-traffic cone. Both fox species showed a neophobic response: bait-station visitation rates decreased (P=0.005 and P=0.048, for Culpeo and Grey foxes, respectively) in the presence of the novel object. The intensity of the response differed between species being higher for Culpeo foxes (approximately 80% of reduction in visitation rate during treatment for Culpeo foxes vs. 10% for Grey foxes). However, the bait-station visitation pattern after novel object removal indicated that animals probably increased exploration of the station. The high level of neophobia achieved by the Culpeo fox, together with an increase in post-treatment site exploration, suggests that behavioural manipulations (reduction of neophobia and its consequent increase in risk taking) could improve selective and efficient fox control in rural areas where livestock production is a major economic activity.

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.

Summer food habits of the Patagonian opossum, Lestodelphys halli (Thomas, 1921), in southern arid Patagonian shrub-steppes

Estudiamos la dieta estival de la comadrejita patagonica Lestodelphys halli en el sureste de la Patagonia Argentina, por medio del analisis de contenidos estomacales provenientes de animales muertos y de fecas. Encontramos una gran variedad de invertebrados (87,2% de frecuencia de ocurrencia) seguido de aves y reptiles (10,64%) tanto en estomagos como en fecas. Los frutos fueron escasos en la dieta. En cautividad, la comadrejita patagonica se alimenta fundamentalmente de roedores, reptiles, aves e invertebrados. Sin embargo, no encontramos restos de roedores en la dieta de la comadrejita. Sugerimos que la comadrejita patagonica no es un predador eficiente de roedores en estado silvestre. El alto consumo de invertebrados, reptiles, aves y frutos durante el verano, cuando estos items son abundantes, refleja el comportamiento oportunista de esta especie.

Diet of the Red-backed Hawk (Buteo polyosoma) in two environmentally contrasting areas of Patagonia

We studied the Red-backed Hawk (Buteo polyosoma) diet by pellet analysis in two areas, the Monumento Natural Bosques Petrificados (MNBP) and Junín de los Andes, located in southern and northwestern Argentinean Patagonia respectively. These areas have different values of primary production mainly due to the differences in mean annual precipitation, being higher in Junín de los Andes. Diets were dominated by mammals in both areas (68.3% and 61% of occurrences). Rodents represented the greatest proportion (66.5%) of prey numbers in MNBP. They represented 92.6% of the biomass. Arthropods were also consumed with a relatively high occurrence (21.4%). In Junín de los Andes, rodents were an important prey (57.1%) but represented only 29.6% of the consumed biomass. In contrast, the introduced European hare (Lepus europaeus) was not frequently consumed (13.5%) but comprised 59.3% of prey biomass. Reptiles were a frequent item, consumed at 25.2% of total prey. The diet of the Red-backed Hawk was significantly different between MNBP and Junín de los Andes. The wider food niche breadth of the Red-backed Hawk in Junín de los Andes was likely attributable to the more even distribution of prey categories. Additionally, a functional response toward European hare consumption was observed, with a higher consumption of this prey at Junín de los Andes. Estudiamos la dieta del Aguilucho común (Buteo polyosoma) por medio del análisis de egagrópilas, en dos áreas: el Monumento Natural Bosques Petrificados (MNBP) y Junín de los Andes, situadas respectivamente en el sur y noroeste de la Patagonia Argentina. La productividad primaria es diferente en ambas áreas, debido principalmente a la cantidad de precipitaciones, que son mayores en Junín de los Andes. Los mamíferos fueron las presas más importantes en la dieta del Aguilucho en ambas áreas (68.3% y 61.0% de ocurrencias). La proporción de roedores en el MNBP fue alta (66.5%), representando el 92.6% de la biomasa total consumida. Otro ítem importante fueron los artrópodos con una ocurrencia del 21.34%. En Junín de los Andes, los roedores fueron también presas importantes en la dieta del Aguilucho común (57.1%), pero representaron solamente 29.6% de la biomasa total consumida. Por el contrario, la liebre europea (Lepus europaeus), una presa introducida, fue consumida con una frecuencia menor (13.5%) pero constituyó el 59.3% de la biomasa total. Los reptiles fueron frecuentemente consumidos (25.2%). En concordancia, la dieta del Aguilucho común fue significativamente diferente entre el MNBP y Junín de los Andes. La mayor amplitud del nicho trófico del Aguilucho común en Junín de los Andes podría ser atribuida a la mayor equidad en la distribución de las categorías presa. Adicionalmente, se observó una respuesta funcional hacia el consumo de liebre europea, siendo mayor en Junín de los Andes.

DIET OF THE AMERICAN KESTREL IN ARGENTINE PATAGONIA

Resumen Presentamos el primer analisis cuantitativo de la dieta de Falco sparverius en el sur de Argentina. Identificamos 1169 items de presas en un total de 272 egagropilas y siete restos de presas de cuatro sitios de estudio en la Patagonia. En esta area, F. sparverius se alimento principalmente de escorpiones (Bothruridae), escarabajos (Coleoptera), hormigas (Formicidae), saltamontes (Acrididae), gorgojos (Curculionidae) y roedores (Rodentia). La dieta difirio significativamente entre los sitios de estudio en terminos de la frecuencia de varios items entre las presas, pero no en terminos de la biomasa. De acuerdo a la frecuencia, los insectos conformaron la mayor parte de la dieta en la mayoria de los sitios, pero los vertebrados contribuyeron mas en terminos de biomasa.