Gerardo R. Cueto

SCURVY IN CAPYBARAS BRED IN CAPTIVITY IN ARGENTINE

In order to determine if the absence of vitamin C in the diet of capybaras (Hydrochoerus hydrochaeris) causes scurvy, a group of seven young individuals were fed food pellets without ascorbic acid, while another group of eight individuals received the same food with 1 g of ascorbic acid per animal per day. Animals in the first group developed signs of scurvy-like gingivitis, breaking of the incisors and death of one animal. Clinical signs appeared between 25 and 104 days from the beginning of the trial in all individuals. Growth rates of individuals deprived of vitamin C was considerably less than those observed in the control group. Deficiency of ascorbic acid had a severe effect on reproduction of another population of captive capybaras. We found that the decrease in ascorbic acid content in the diet affected pregnancy, especially during the first stages. The results obtained suggest that it is necessary to supply a suitable quantity of vitamin C in the diet of this species in captivity.

VARIATION IN THE DIET OF WESTERN BARN OWLS (TYTO ALBA) ALONG AN URBAN-RURAL GRADIENT

Abstract We studied geographic variation in the diet of Western Barn Owls (Tyto alba) along a urban-rural gradient in central-eastern Argentina and identified 5,231 prey items. Mammals were present in all samples, whereas birds and amphibians were present in 79.1 and 50.0% of the samples, respectively. There were significant differences in vertebrate assemblages consumed by Barn Owls at the opposite extremes of the gradient. Native sigmodontine rodents comprised 85.8% of the total prey items, especially towards periurban and rural areas. Exotic murid rodents were the main prey item in urban sites, while birds increased in frequency in urban and periurban areas. Food niche breadth and standardized food niche breadth values were higher at intermediate levels of urbanization ( =  periurban). This ‘periurban peak’ in species diversity is a relatively well-known pattern, previously reported for taxa such as birds, lizards, bumblebees, and butterflies among others. The trophic habits of Barn Owls along this gradient were mostly similar to those reported in other studies in southern South America, where the main prey items were native rodents and food niche breadth values (measured at the level of Orders) were low. Western Barn Owls in our study maintained specialization as a micromammal predator.

Hair structure of small rodents from central Argentina: A tool for species identification

Abstract Mammal hairs differ among species and may therefore be used for diagnoses at the species level. We characterized dorsal guard hairs of most small rodent species that may be found in central Buenos Aires province (Argentina), according to their geographic distribution: Cavia aperea, Rattus rattus, R. norvegicus, Mus musculus, Holochilus brasiliensis, Scapteromys aquaticus, Oxymycterus rufus, Oligoryzomys flavescens, Akodon azarae, Deltamys kempi, Calomys laucha and C. musculinus. We provide discriminant functions and a dichotomic key to identify hairs at the species level based on hair length and width and scale morphology observed in specific sections of dorsal guard hairs. Discriminant functions require fewer measurements and are faster than the use of the key.

Techniques to Estimate Abundance and Monitoring Rodent Pests in Urban Environments

Different techniques have been developed in order to study the ecology of animals. The application of each technique depends on the studied animal species, on the type of habitats where they live and the objectives of the study. Most of the ecological studies focus on a unique population, which is defined as a group of organisms of the same species that coexist at the same time and in the same area (Krebs, 1978); or on a community, which is defined as a group of populations that exist at the same time and in the same area (Begon et al., 1987). One of the most important characteristics of a population is its size or abundance. This is determined by the number of individuals born, the number of individuals that dead and the number of individuals going into or out of the area that the population occupies per unit of time (Begon, 1979; Krebs, 1978). On the other hand, some of the characteristics of the animal community are the species composition, its absolute abundances and relative abundances, the richness, dominance, diversity, equitability, trophic structure and the niche structure (Krebs, 1978). Except for the trophic and niche structure, the other characteristics mentioned above are inferred from the abundances of the individual species that make up the community.

Comparison of efficacy of second-generation anticoagulant rodenticides: Effect of active ingredients, type of formulation and commercial suppliers

Abstract The lack of a standardized protocol makes it difficult to compare studies on the efficacy of commercial rodenticides. To contribute to the knowledge of pest control technology, we compared the efficacy of 17 commercial baits with different active ingredients and types of formulation from various commercial suppliers, using a standardized efficacy protocol under laboratory conditions. All rats died in all experimental groups. First deaths occurred 3 days after the beginning of the trial; average survival varied between 4.17 ± 0.12 days (difethialone wax blocks) and 5.96 ± 0.35 days (difenacoum pellets). Results showed no consistent pattern of time to death according to active ingredient and type of formulation. For bromadiolone-based baits, the grains induced significantly shorter time to death than wax blocks and the individuals fed on wax blocks varied the consumption rate according to the commercial supplier, while those consuming grains showed more homogeneous values. Our results show that although mortality was 100% efficacy differed among baits. These differences could be explained by the combination of the formulation type and commercial supplier rather than by the active ingredient itself.