ANALYSIS OF THE NEST ENVIRONMENT OF TUATARA SPHENODON-PUNCTATUS

Water potential and temperature were monitored in 20 natural nests of tuatara, Sphenodon punctatus, through 12 months of incubation on Steph ens Island, New Zealand. Tuatara nest in rookeries in open pasture, in sites that often are more than 100 m from residential burrows located beneath the closed canopy of native bush. Nest tunnels are approximat ely 197 mm long, 73 mm wide, and 45 mm high, and have a slightly expan ded chamber al the end. Eggs are generally deposited in 1-3 layers in the terminal chamber. The top eggs are 30-155 mm below the soil surfac e, and an air space of as much as 20 mm may exist between the uppermos t egg and the top of the chamber. Each nest receives an average of 8-6 eggs that imbibe water and swell during incubation. Only 48% of eggs have hatched or are still alive 12 months after oviposition. Survival by embryos is higher in moist nests than in dry ones. Variation in tem perature in nests has only a small influence on survival, and this inf luence may be mediated indirectly by effects of temperature on the wat er exchanges experienced by incubating eggs. Water potentials in the s oil of closed canopy forest on Stephens Island are high enough to supp ort embryogenesis, but temperatures are too low. Thus, females leave t he forest to nest in areas where soil temperatures are for incubation.