The design of many shelters for laboratory mice, particularly plastic shelters, is mainly driven by economic, ergonomic and hygiene considerations, with little focus on providing the animals with opportunities to express species-specific behaviours and control over their environment. Even in the presence of artificial shelters (plastic houses, tunnels), laboratory mice will readily burrow if given the opportunity. The main aim of this study was to gain a better understanding of the importance of access to sheltered space for laboratory mice. We pair-housed mice (BALB/c, SWISS and C57BL/6, male and female) in conventional laboratory cages that contained either (i) resources to build underground shelter (burrowing substrate) or (ii) artificial structures providing shelter (e.g. red plastic house). We assessed how mice used these resources, as well as their preferences when given a choice between different shelters. In addition, we assessed the insulating properties of different shelters. Mice spent most of their time underground in deep bedding and the least time inside the standard red plastic house, where they nested outside the house. They also showed a strong preference for the deep burrow cage, and the most relevant features of preferred shelters seem to be darkness and being underground. Nesting material alone was also less insulating, possibly contributing to an increased need for non-shivering thermogenesis.
