María Busch

Effects of Food Supplementation on Rodents in Winter

We evaluated the role of food availability on population parameters of rodents in agroeco-systems in the Pampas of Argentina by mark-recapture studies in six crop-field borders; three controls and three areas with supplemental food. Akodon azarae , the pampean grassland mouse, in supplemented borders exhibited increased density, more immigration, greater persistence, greater proportion of pregnant females, and increase in mean mass and length. We conclude that food availability is a factor contributing to winter reduction and slow springtime increase in density of A. azarae .

Environmental factors associated with rodent infestations in Argentine poultry farms

Abstract 1. Seasonal variations in rodent infestations were studied at poultry farms in central Argentina as well as the environmental factors associated with rodent infestations at poultry farms. 2. During the summer and winter of 1998 rodent infestation was monitored at 10 poultry farms by means of tracking stations, and 21 environmental variables were selected that a priori could be related with the extent of rodent infestation. 3. There was a higher rodent infestation in winter than in summer. 4. Species detected by rodent sightings at the poultry farms included Akodon azarae, Calomys spp. (C. laucha and possibly C. musculinus) and Mus musculus. 5. In summer, rodent infestation was positively associated with the perimeter of the farm, whereas there was an inverse relationship with the maintenance conditions of the sheds. In winter, rodent infestation was positively associated with the percentage of the borders of the farm covered with vegetation, and with the amount of plant cover, especially the amount of plant cover which was above 20 cm in height. 6. There was no significant relationship between rodent infestation and the time lag since the last application of rodenticide (first-generation anticoagulant) at the farms. 7. These results suggest that strategies for controlling rodents based solely on chemical methods may not be good enough for efficient rodent control. Farms which are properly managed, with a better control of vegetation growth at both the perimeter and within the internal area, in addition to a higher maintenance of sheds have appreciably lower rodent infestations.

Density-dependent habitat selection between maize cropfields and their borders in two rodent species (Akodon azarae and Calomys laucha) of Pampean agroecosystems

We studied habitat preferences and intra and interspecific density-dependent effects on habitat selection by Akodon azarae and Calomys laucha between maize fields and their adjacent borders, during different developmental stages of the crop. Akodon azarae detected quantitative differences between habitats, using preferentially borders throughout the year, while C. laucha perceived borders and cropfields as quantitatively similar during spring and summer and it detected borders as quantitatively better at the high density period (autumn and winter). These results support the prediction of differential habitat preferences as a model of community organisation at the low density period, while they are consistent with shared habitat preferences during autumn and winter when both species apparently coexist in the better habitat (border). Akodon azarae showed intraspecific density-dependent habitat selection throughout the year, except in spring, while habitat selection by C. laucha was density-dependent in spring, autumn and winter. The effect of interspecific density on habitat selection was detected in both habitats and changed seasonally. The effect of A. azarae over C. laucha by resources exploitation was detected in borders, while competitive effects of C. laucha over A. azarae was observed within cropfields. Both species were more affected by exploitation competition than interference, which was more common in borders than in maize fields. We conclude that seasonally have a profound effect in habitat selection of these species because it changes the intensity of intra and interspecific competition and affects different habitat preferences and basic suitability of habitats.

Bromadiolone susceptibility in wild and laboratory Mus musculus L.(house mice) in Buenos Aires, Argentina

BACKGROUND Rodents are major pests in many agricultural systems, where they can cause significant economic losses and involve a sanitary risk. The application of anticoagulant rodenticides for rodent control has showed a decrease in effectiveness through time because of the development of resistant populations and the development of aversion behaviour. The goal of the present study was to test the susceptibility to bromadiolone and the existence of anticoagulant resistance in Mus musculus L. (house mouse) in Argentina. We conducted a feeding test with wild animals captured in poultry farms and a laboratory strain that were fed with bromadiolone bait. RESULTS Three animals of the field experimental group survived the 21 days study period, while for laboratory animals mortality was 100%. Control field animals which were fed without anticoagulant showed 100% survival. CONCLUSION We found evidence of the presence of anticoagulant resistant M. musculus L. in the study area. Feeding behaviour may have contributed to increasing the time of survival, and may be a mechanism that allows metabolic clearance of the bromadiolone. Under field conditions control with anticoagulants would be less effective because animals have alternative food.

Intra-farm variation of rodent infestations on poultry farms of central Argentina

1. During the summer and winter of 1998 we monitored rodent infestation in the sheds of 9 poultry farms in central Argentina to estimate variation in rodent infestation within farms and its possible association with shed structure and farm design. 2. We observed great heterogeneity in rodent infestations, with a mean variation of 37% in the ‘Rodent Infestation Index’ (RII; an estimate of rodent density revealed by tracks) between sheds of the same farm. 3. In summer, the group of sheds that showed the highest RII had a higher chicken density than the group of sheds with the lowest RII. Sheds located between other sheds of the same farm showed a lower RII than sheds located beside the perimeter of the farm. 4. Our results support the hypothesis that rodents show habitat selection at both macro (farm) and microhabitat (shed) scales, and that the variables associated with these associations can change according to the scale. 5. Our observation that sheds located beside the perimeter of the farms are prone to rodent invasions reinforces our previous recommendation that farms with an efficient control of vegetation growth around their perimeter would have appreciably lower rodent infestations.

Foraging activity of commensal Mus musculus in semi-captivity conditions. Effect of predator odours, previous experience and moonlight

BACKGROUND Mus musculus is a pest in urban and rural habitats where it consumes and contaminates food and may transmit diseases to human and domestic animals. Its control by anticoagulants is partially effective because of aversive behaviours and resistance. In this context, we wanted to assess the potential of the use of predator odours as repellents in experimental feeding trials using urine and faeces of domestic cats and faeces of geoffroyi cat, a wild small felid that is one of the main rodent predators in the study area. We also assessed the effect of previous experience and moonlight on foraging activity. RESULTS We did not find an aversive response to cat odours in Mus musculus individuals. There was a trend to consume food in the same feeding stations over time, and the visit rate was lower in periods with high moonlight than in periods with low moonlight. CONCLUSIONS Predator odours did not seem to be useful as rodent repellents, but maintaining illumination may lower rodent foraging activity. As rodents maintain their feeding sites over time, toxic baits may be more efficiently placed at sites previously known to be used by rodents.

Evaluation of statistical methods and sampling designs for the assessment of microhabitat selection based on point data

1.Information on resource selection by a species is essential for understanding the species’ ecology, distribution and requirements for survival. Research on habitat selection frequently relies on animal detection at point locations to determine which resource units are used. A variety of approaches and statistical tools can be employed for assessing selection based on habitat variables measured in those units. The aim of this work is to evaluate the reliability of common sampling designs and statistical methods in detecting habitat selection at fine scales based on point data 2.We reviewed literature on microhabitat selection to determine characteristics of typical studies and analysed simulated small mammal live-trapping data as a case study. We considered various scenarios differing in the number of sampled units and sampling duration. For each scenario, a set of simulated surveys was analysed through two univariate tests (Welchs t- and Mann-Whitney U-test), generalised linear models (GLMs), mixed-effect models (GLMMs) and occupancy models (OMs). 3.Analysis of simulated data revealed that overall performance of all statistical methods improved with increased trapping effort. Univariate tests were especially sensitive to the number of sampling units, while modelling methods took also advantage of longer trapping sessions. Univariate tests and GLMs provided partially correct information in most cases, whereas GLMMs and OMs offered higher probabilities of fully describing simulated habitat preferences. 4.With typical sampling efforts, appropriate statistical analysis of point data is able to provide a moderately accurate description of habitat selection at small scales, in spite of the violation of closure and independence assumptions of applied models. Modelling approaches are proliferating; we encourage using models that can deal with multiple sources of variability, such as GLMMs and OMs, when data are hierarchically structured. There is no a priori best survey design; it should be chosen according to the scope and goals of the study, environment heterogeneity, species characteristics and practical constraints. Researchers should realise that sampling design and statistical methods likely affect conclusions regarding habitat selection. This article is protected by copyright. All rights reserved.

The effect of neighbourhood on rodent communities: an example from Pampean agroecosystems

Abstract Pampean region agroecosystems are devoted to agricultural and farming activities, but in the crop field matrix there are relicts of remnant natural habitats. Poultry farms mainly harbour commensal species as house mice and rats, which are rarely present in surrounding habitats. We assessed if neighbourhood to poultry farms affect the presence of Mus musculus in crop fields and their borders, and if rodent community in poultry farms is influenced by the species present in surrounding crop fields and borders. We found that habitat had a significant effect on the abundance of M. musculus. This species showed higher abundance in poultry farms than in crop field borders. Calomys laucha was the unique native species that was captured in farm sheds. We found higher abundance of native species in crop field borders than in crop fields independent of the proximity to the poultry farms. We conclude that rodent communities in poultry farms are little influenced by the surroundings, and show a dominance of M. musculus independently of the presence of native rodent species in neighbour habitats. On the other hand, farms do not export M. musculus to surrounding habitats, and borders only function as corridors for dispersal among farms, while crop fields are rarely used.