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.