Abstract
The size of nest boxes induces contrasting effects on exploratory behaviour and nest establishment of mice. Nest box exploration increases, and preference for nest site decreases, with increasing nest box size (Buhot, 1987). The aim of the present study was to continue the investigation of the different effects of the inner vs outer properties (here sizes) of nest boxes, the former being likely to play a major role in nest establishment, whereas the latter were predicted to be mainly involved in the initial exploratory process. The subjects were cagemate groups of two or three male mice. They were subjected to four ranking tests in which the nest boxes differed in outer size only, or in inner size only, and they either had a roof or did not have one. Among nest boxes with identical inside dimensions, the mice preferentially chose as nest sites those with the largest available outer dimensions; the presence of a roof did not affect this preference. In situations with nest boxes differing only in inner size, opposite preferences were observed, depending on whether or not a roof was present. In the presence of roofed nest boxes, mice's preferences were positively correlated with the size of the boxes. In the unroofed condition, an optimal value was observed around the second smaller inner-spaced nest box. Thus, both inner and outer properties influenced nest box choice. As a roof provides maximum safety, its presence seemed to have allowed choice to be governed by a secondary criterion—the maximum distance between the nest and the entrance. Initial exploration patterns were mainly influenced by the outer characteristics of the nest boxes: the larger the nest boxes were on the outside, the earlier and more frequently they were visited.
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