Potential competitors that eat each other can engender patterns of spatial segregation similar to those produced by competition, and distinguishable only by field manipulation. This paper reports the results of a perturbation experiment to test the factors responsible for small-scale discontinuities in the distribution of a common insectivore. Populations of hedgehogs (Erinaceus europaeus) were monitored following their introductions into an area where they had been absent, and into a neighbouring area where they were known to persist. The two sites had a similar availability of preferred habitat, and the growth rates of introduced hedgehogs were similar. The density of badgers (Meles meles), larger members of the same guild, appears to produce differences in mortality and dispersal, which returned the populations close to their original levels within 2 months of the transplant.