Factors involved in the recovery and reinstatement of a territorial resident's aggression directed at an intruder after habituation were studied in the Three-spined Stickleback (Gasterosteus aculeatus). In the first experiment it was demonstrated that following initial habituation to the intruder, there was no recovery of response after 3-5 days, but there was virtually complete recovery after 14 days. It was further shown that if the stickleback's nest is removed and he rebuilds the nest between the first habituation session and the test, there is complete recovery following nest reconstruction. A second series of experiments shows that the recovery following nest removal and reconstruction is prevented if the fish is prevented from reconstructing the nest. It was further found in two additional sub-experiments that allowing post-habituation nest reconstruction appeared to re-set memory for the habituated stimulus such that the intruding stimulus fish appears novel to the territorial resident, thus abolishing the stimulus specific nature of such habituation.