Solitary behavior at high population density in tuco-tucos (Ctenomys sp.) from Parque Nacional Los Cardones, Argentina.

This article focuses on the social organization and population density of a tuco-tuco population (genus *Ctenomys*) in Valle Encantado, Parque Nacional Los Cardones, Salta Province, Argentina. Despite an exceptionally high adult density (~75 adults per hectare), radiotelemetry and live-trapping data indicate that individuals are solitary, each occupying distinct burrow systems and nest sites, with minimal spatial overlap and rare co-occurrence in space and time. Phylogenetic analysis using mitochondrial cytochrome b sequences revealed that these tuco-tucos are not part of the previously suggested *opimus* subclade but are more closely related to the *magellanicus* and *tucumanus* subclades. Comparative data across *Ctenomys* species show no clear relationship between population density and social organization, highlighting the complexity of factors influencing solitary versus group living in subterranean rodents.