The tuatara, Sphenodon punctatus Gray, on islands with and without populations of the Polynesian rat, Rattus exulans (Peale).

The results of a survey of the presence and populations of the tuatara (Sphenodon punctatus) and the Polynesian rat or kiore (Rattus exulans) on 35- islands off the New Zealand coast are presented and discussed. Tuataras were found on 23 of these, and on six they occur with kiore. The age distributions and densities of the tuatara populations suggest that decline because of failure of recruitment is occurring on seven—the six kiore -inhabited islands and one other. Seven more kiore-inhabited islands within island groups which otherwise support tuataras apparently lack any tuataras themselves. These findings strongly suggest that tuataras cannot persist in the presence of this rat