Space use by Río Negro tuco-tucos (Ctenomys rionegrensis): Excursions and spatial overlap

Patterns of spatial overlap can provide important insights into a species’ social organization. Subterranean rodents are notable for their lack of intermediate social systems in which individuals overlap spatially with one another but occupy distinct burrows. Previous studies of Río Negro tuco-tucos (Ctenomys rionegrensis) have revealed that while multiple adults can be captured at the same burrow entrance, these animals do not display other traits characteristic of social tuco-tucos, leading us to suspect that C. rionegrensis may exhibit an intermediate form of spatial and social structure. To test this hypothesis, we used radiotelemetry to monitor spatial relationships among adult C. rionegrensis during May, September, and November of 2005. Comparisons of minimum convex polygons for these animals revealed spatial overlap between 3 pairs of neighboring adult females. Most instances of spatial overlap occurred during November, which was the sampling period characterized by the largest number of radio fixes per animal and, accordingly, the largest individual home ranges. The observed examples of overlap appeared to reflect occasional excursions by one individual into the burrow system of another adult. These findings are consistent with an intermediate pattern of space use, suggesting that C. rionegrensis exhibits a spatial structure not previously documented among ctenomyids or other subterranean rodents.