Circadian and ontogenetic changes in activity and anti-predator responses of captive juvenile tuatara (Sphenodon spp.)

Abstract

Behaviour is a fundamental part of the ecology of any animal and is important for its survival and subsequent fitness. Knowledge of the behaviour of rare species can help scientists understand their population dynamics and persistence. This knowledge may then be applied to management procedures. In the wild, behavioural traits evolve in response to specific selection pressures, such as competition for resources, predation, and thermal requirements. However, in captivity selection pressures are relaxed, resulting in changes in behaviour, which may affect the survival of captive-reared individuals upon release into the wild. Tuatara (Sphenodon spp.) are rare reptiles, endemic to New Zealand. Head-starting is used as a tool for the conservation of tuatara, yet the effects of captive-rearing on the behaviour and subsequent post-release survival of tuatara are not known. I investigated circadian changes in emergence, activity, territoriality, and anti-predator responses in two- and three-year old S. guntheri and five-year old S. punctatus. I also re-analysed anti-predator response data available from another study on the same S. punctatus, tested at one, six, and 10 months of age. Juvenile tuatara emerge predominantly at night, but are most active, that is, move around above ground, mainly during the day and around sunset. The level of territoriality was consistently high throughout the 24 h period, potentially due to its importance in resource acquisition. Juvenile tuatara were significantly more likely to flee from predator models than to freeze. The likelihood of fleeing was higher during day. A decrease in flight tendency was observed during the first 10 months of age, but increased from the age of 10 months to five years in S. punctatus, possibly as a result of the intense monitoring regime during the first 10 months. Nocturnal emergence and crepuscular activity may be driven by the high abundance of resources (e.g., insects) after sunset and the lower likelihood of detection by visually-hunting predators. However, low nocturnal temperatures restrict locomotor ability, limiting movements and active anti-predator responses (i.e. flight) to day-time. Handling may affect behavioural responses of captive tuatara to predators. Anti-predator behaviour has consequences for the survival of released individuals and establishment of new populations founded on captive-reared animals. 1 recommend handling is kept to a minimum throughout head-starting. I also advise that a quantitative study on post-release tuatara is conducted to establish whether the survival of individuals is correlated with flight responses to predator models in captivity.