In nature, mice live in burrows with nest chambers where they breed and may hide from predators. In the laboratory, a shelter or refuge is an easily applicable form of enrichment which may enhance the welfare of laboratory mice by giving them more control over their environment. Six nest boxes made of different materials were evaluated in a preference test with male and female mice of two strains (C57BL/6J and BALB/c). In general, mice showed a preference for cages with a nest box made of grid metal as compared to clear or white perspex nest boxes, or no nest box. They also showed a preference for a cage with a nest box of perforated metal as compared to nest boxes made of grey PVC or sheet metal, or no nest box. When offered a nest box with one open side or a nest box with two open sides, most mice preferred the nest box with one open side and were observed to lie in it with their heads directed towards the opening.

The results of this study show that nest boxes may be used for enrichment purposes in caged mice, although it is not yet entirely clear what are the main features influencing the animals’ preferences. When providing nest boxes as shelters, the structure and design of this type of enrichment should be taken into account, because these may have an effect on the social structure of groups of mice.

Motivation is a central concept for animal welfare; it has inspired methodological breakthroughs and generated a wealth of crucial empirical work. As the field develops beyond its original mandate to alleviate the suffering of animals in intensive farming systems, the assumptions behind the current models of motivation may warrant closer scrutiny. In this paper, I examine some of the complexities of studying motivation — for example, that what an animal wants can depend on its welfare and that, through genetic selection and housing choices, we can modify what an animal finds to be rewarding versus punishing. The central theme of this paper is, therefore, that we cannot just ask the animals under our care (or even in the wild) what they want and assume that we will receive unadulterated answers, free from human influence. While asking questions about animal motivation with empirical research is invaluable and necessary, our models drive our research questions, methodologies, and results’ interpretation. When the models we employ remain implicit (eg the only motivation questions worth asking are those that could be implemented within the current housing systems), they have ability to stifle progress in understanding animal welfare. Thus, in addition to the empirical work, we also need to expose and evaluate the models that drive the research. Making the models explicit will facilitate our ability to identify their areas of silence, assess their strengths and potential limitations, as well as examine how they conceptualise the relationship between motivation and animal welfare. I end with a discussion of the implications of a few relevant models, both implicit and explicit, noting how such consideration reveals exciting areas for future work, including, for example, research on the motivation to make choices and the motivation to learn.