Tuatara (Sphenodon punctatus) feeding ecology in the presence of kiore (Rattus exulans)

Abstract

The diet of tuatara was investigated on kiore‐inhabited Lady Alice Island in the Hen and Chickens Group, northern New Zealand, between 1993 and 1994. Both dietary (targeted) and inedible (incidental) items were eaten by tuatara. Dietary items recorded were exclusively invertebrate in origin. Estimates of environmental availability of invertebrates and indicated that the prey consumed were strongly selected by size and by taxa. Beetles, insect larvae, arachnids and weta comprised the greatest proportion of total diet, appeared in the greatest number of stomachs and were taken in excess of their abundance. Most prey were >10 mm in length, despite an abundance of smaller prey in the environment. The risk of predation by tuatara was greatest for terrestrial invertebrates and least for arboreal species. The composition of diets by habitat was largely similar between mid‐successional kanuka (Kunzea ericoides) and late successional mixed broadleaf forest. The size distribution of prey eaten by tuatara in kanuka habitat during autumn, and the low number of tuatara yielding dietary samples, are discussed in terms of food competition with kiore. Overall, the foraging behaviour of tuatara was not obviously different on rodent‐free compared to kiore‐inhabited islands, either indicating that food competition is insufficient to influence diet, or that tuatara are unable to change their feeding behaviour under a higher degree of competitive pressure for prey items. Clear support for either hypothesis is lacking.