Studies on the motivation for burrowing by laboratory mice

Several species of mice build burrows, however, little is known about the motivation underlying this behaviour. This study had two aims: (1) to investigate whether burrowing constitutes a behavioural need, that is, whether mice were motivated to perform the behaviour of burrowing per se, or whether it is the functional consequences of burrowing that motivate the behaviour; (2) to determine the strength of motivation that laboratory mice have for burrowing. In Experiment 1, eight BALB/c mice were placed individually into a start cage connected to two burrowing compartments containing peat. During Phase 1, the mice had access to only one compartment, and during Phase 2, access to only the second. At the beginning of Phase 3, the burrows in one of the compartments were destroyed and the mice given access to both. The duration of burrowing remained unchanged throughout all three phases, and the number of burrowing bouts significantly increased. During Phase 3, there was no significant difference between burrowing in the compartments containing the intact or the destroyed burrows. These data confirmed that laboratory mice readily build burrows when given the opportunity, and indicate this behaviour constitutes a ‘behavioural need’. In Experiment 2, the strength of motivation for burrowing was examined in five CB57 mice using an operant technique in which a single mouse within a group could work to gain access to burrowing substrate. Despite increasing cost of gaining access, the mice continued to work to visit the burrowing substrate. The slope and area under the demand function indicated that the motivation to build burrows was high. These findings indicate that if studies require laboratory mice to express a full behavioural repertoire, or to avoid compromises of welfare, mice should be provided with the opportunity to perform burrowing wherever practicable.