Structural complexity of territories: preference, use of space and defencein commensal house mice, Mus domesticus

Previous studies suggest the physical structure of a habitat has profound e ffects on intraspecific competition and spacing behaviour among small mamma ls. We compared habitat preferences and the exploratory behaviour and aggre ssive territorial defence of male house mice in three types of enclosure di ffering only in their degree of structural complexity. Each enclosure conta ined a nestbox placed in one corner, a central food hopper and 10 house bri cks. The bricks were either placed around the outer walls (open enclosures) , lined up across the middle (wall enclosures) or scattered separately acro ss the floor (complex enclosures). In pairwise choice tests, mice showed a strong preference for wall or complex enclosures over open enclosures but n o preference between wall and complex enclosures. They were more active thr oughout the enclosure with complex structuring and stayed near the side wal ls in open enclosures. Residents in open enclosures initially showed a lowe r rate of attack and duration of pursuit when faced with an intruder but no t when faced with a second intruder. In complex enclosures, nearly all enco unters ended because the residents continued pursuit but lost track of the intruder. This occurred in only half of intruder pursuits in open and wall enclosures. Our results suggest that mice prefer areas containing physical structure because this provides a degree of protection from predators but t erritories with complex physical structuring appear to be much more difficu lt to defend. Complex areas may thus support a higher density of mice than open areas or those with more simply aligned physical structuring. (C) 2000 The Association for the Study of Animal Behaviour.