During 1984 an unsanctioned farm road was constructed through the known range of McGregor's skink (Cyclodina macgregori) on Mana Island (217 ha). Monitoring of the island's lizard populations commenced in 1986 to assess the effects of habitat changes caused by the construction of the road. Between 1987/88 and 1988/89 the capture rate (pitfall traps) for McGregor's skink declined significantly. This decline is attributed to increased predation by mice (Mus musculus) following a buildup of mouse numbers after cattle (the only stock then present) were removed from the island in 1986. In August 1989 a successful programme to eradicate mice was implemented, and no mice or their sign have been seen since February 1990. Since then, the capture rates have increased significantly for C. macgregori, the gecko (Hoplodactylus maculatus), and the Cook Strait giant weta (Deinacrida rugosa) (Orthoptera). Even though individual C. macgregori show strong site fidelity and are potentially longlived (10+ years), only three of 64 caught to April 1988 have been recaptured since the last mouse was trapped. Adults appeared more vulnerable to predation than juveniles. All captures of McGregor's skink on Mana Island were made within a small area (<5 ha) along the north-east coast; within this area, shrub cover is increasing relative to that of grasses and herbs.

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Radiography was used to determine the proportion of female tuatara, Sphenodon punctatus, that carry eggs each year, over 6 years on Stephens Island and 5 years on Lady Alice Island. The smallest female found to be gravid, located on Stephens Island, was 170 mm snout-vent length. Between 1983 and 1987 the gravidity rate for Lady Alice Island females averaged 28.8% (range = 22.2-45.5%), while between 1982 and 1987 the gravidity rate for Stephens Island females averaged 21.9% (range = 8.2-29.6%). Excluding data from 1986, when only 11 females from Lady Alice Island were sampled, annual gravidity rates did not differ significantly between islands. There was significant annual variation in the proportion of females carrying eggs on Stephens Island, but not on Lady Alice Island. On Stephens Island, gravidity rate was especially low in 1982 (8.2%). There were significant positive, but different, correlations between clutch size and female body size on both islands. Mean clutch size for Lady Alice Island females (7.9 eggs; range = 5-13 eggs) was significantly smaller

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Invasive mammalian predators such as rats are now widespread on islands, but hypotheses about their effects have rarely been tested. Circumstantial evidence from New Zealand indicates that, when introduced to islands, Pacific rats (Rattus exulans) have negative effects on endemic plants, invertebrates, birds, and reptiles, including the tuatara (Sphenodon punctatus). We tested the effects of Pacific rats on tuatara by comparing the demographic structure and body condition of tuatara populations on three islands before and after removal of rats and on a fourth island where rats remained. In the presence of rats, juvenile tuatara constituted on average 0-5% of the sample tuatara populations. When Pacific rats were removed after at least 200 years' occupancy, the proportion of juvenile tuatara increased 3.5- to 17-fold and body condition of adult males and females also improved (sometimes dramatically). We predict that, unless Pacific rats are removed from Taranga Island, the tuatara population will collapse because of low population density and the lack of juvenile recruitment. Our results demonstrate that when invasive species exert subtle effects on recruitment and body condition, the effects on populations of long-lived endemic species may only become apparent long after the invasion.