Consumer demand theory has been used to assess the environmental requirements of domestic animals, because they will defend consumption of important resources, but not consumption of less important resources as their cost is increased (Dawkins, 1983). A commonly used approach is to place the cost on access to the resource, where once the animal has overcome the cost of access, there is no limit on time spent with a resource. So animals can compensate for fewer visits by spending longer with the resource on each visit (Sherwin and Nicol, 1995, Cooper and Mason, in press), in which case price paid and amount consumed may not covary, which would contravene the assumptions underlying the construction of demand functions (Mason et al., in press). In this experiment we investigated one solution to this problem: increasing the entry fee until the subject ceases to gain access to each resource.