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Sphenodon guntheriBrothers Island tuatara

By Amanda Johns

Geographic Range

Brothers Island tuataras inhabit North Brother Island in Cook Straight, New Zealand (41°06′S, 174°26′E). Only a few hundred individuals remain on North Brother Island. (Cree, 1994; Lutz, 2005; Mitchell, et al., 2008; Thompson, et al., 1992)

Habitat

Brothers Island tuataras are one of the few reptiles with the ability to thrive in cooler conditions. They are nocturnal and physically capable of withstanding temperatures as low as 9°C, with humidity in the range of 70 to 80%. High humidity and low temperatures allow tuataras to maintain healthy shed cycles and live longer life spans, due to their effects on heart and metabolic rates. During the day, most individuals inhabit burrows along cliff faces. Their burrows can measure about 5 meters in length and 30 centimeters in depth, and are sometimes taken over from previous inhabitants. Burrows are typically found in open areas featuring low coastal vegetation, and usually offer both shade and sunlight to aid in heat regulation. Certain cliffs and other areas of the island that provide different types of terrain are often inhabited by birds or other animals that can compete with tuataras for territory. (Cree, 1994; Lutz, 2005; Mitchell, et al., 2008; Nelson, et al., 2002a; Ramstad, et al., 2007)

  • Range elevation
    87 (high) m
    285.43 (high) ft

Physical Description

Tuataras generally have a lizard-like appearance, but differ from lizards in that their teeth are attached to bone, they have two temporal openings, they have no external ear, and the males lack sexual organs. Tuatara means “bearing spines”, referring to the single row of spines running along their dorsal side. The skin of this species is generally olive-brown with yellowish patches, which offers effective camouflage in their environment. When born, tuataras possess a third eye on the top of their head (called a parietal eye). This pineal spot appears somewhat functional at birth, but becomes covered with skin after several months and does not appear to serve a functional purpose thereafter. Adults are fairly large and rather slow moving, reaching a weight of 900 g and a length of 76 cm. Males are larger than females and have proportionately larger heads and crests. (Cree, 1994; Lutz, 2005; Pope, 1956)

Brothers Island tuataras belong to the order Rynchocephalia, which contains only one other living species, Sphenodon punctatus (spotted tuataras). Brothers Island tuataras are characteristically smaller and have longer reproductive cycles than spotted tuataras. (Cree, 1994; Lutz, 2005; Pope, 1956)

  • Sexual Dimorphism
  • male larger
  • Range mass
    900 (high) g
    31.72 (high) oz
  • Range length
    76 (high) cm
    29.92 (high) in

Development

In tuataras, incubation temperatures above 22°C tend to produce males, while temperatures of 20°C and below result in more female offspring. Young tuataras escape their eggs by using an egg tooth. This structure is located on the tip of their head between the nostrils and is lost after the first couple of weeks. Newly hatched tuataras resemble miniature versions of adults, and grow very slowly, taking as long as 35 years to reach adult sizes. (Cree, 2002; Lutz, 2005; Mitchell, et al., 2006; Nelson, et al., 2002a; Nelson, et al., 2010)

Reproduction

Little is known about the social structure of mating systems in tuataras, but males tend to be highly territorial and mate with multiple females if given the chance. Male tuataras generally outnumber females in their native environments. Copulation consists of a male mounting a female and excreting sperm from the cloaca. (Cree, et al., 1991; Cree, 1994; Lutz, 2005; Newman, et al., 1994)

Female tuataras reach sexual maturity at 10 to 20 years. Tuataras have long life spans and prolonged reproductive cycles. Females usually dig nests in soil located on cliff edges. Tuataras on North Brother Island produce an average of 1.27 eggs per year for each mature female. The mean clutch size of Brothers Island tuataras is approximately 6.5 eggs. Each egg has a mean weight of 4.9 grams, and the shell has a white coloration with a rather soft texture. Tuataras may lay eggs as often as every 2 years, but most lay eggs every 4 to 5 years. They mate in late summer (December through February in New Zealand), with eggs being layed the following spring. (Cree, et al., 1991; Cree, 1994; Hall, 2007; Hemphill, 2012; Newman, et al., 1994)

  • Breeding interval
    Tuataras typically breed every 4 to 5 years.
  • Breeding season
    Tuataras mate in late summer and lay eggs during the spring. Eggs undergo an incubation period of 12-16 months.
  • Average number of offspring
    6.5
  • Range gestation period
    8 to 10 months
  • Range age at sexual or reproductive maturity (female)
    10 to 20 years

Females invest energy in their young via the production of egg yolks and shells. Once the eggs are laid, neither parent protects the eggs. There is also no parental investment post-hatching. (Hall, 2007)

  • Parental Investment
  • no parental involvement

Lifespan/Longevity

There is some debate regarding the full extent of tuatara lifespans, but they are known to be able to live for over 100 years. Their longevity is mainly due to their slow metabolism and low body temperatures. Little is known about the lifespan of tuataras in captivity, as they are not generally kept as pets. (Lutz, 2005; Nelson, et al., 2002b; Ramstad, et al., 2007; Thompson, et al., 1992)

  • Range lifespan
    Status: wild
    100 (high) years
  • Typical lifespan
    Status: wild
    60 to 100 years

Behavior

The weather plays a role in tuatara activity levels. Even though they are capable of withstanding lower temperatures than most other reptiles (as low as 9°C), their activity level will decline in colder weather. There is some debate as to whether tuataras actually hibernate, but it is believed that on colder nights they can maintain a sort of torpor. Humidity on North Brother Island is typically 70-89%; lower percentages can result in activity suppression and a preference to remain in burrows. (Hall, 2007; Lutz, 2005; Walls, 1983)

Older tuataras are active from dusk until dawn and emerge from burrows mostly at night. Young tuataras are often diurnal, as their faster speed allows them to escape predation. Older tuataras are will set up territories that they defend with displays or physical attacks. The most commonly performed territorial displays include forward approaches, inflation of the body, raising of the crest, head bobbing from side to side, and mouth gaping. (Gillingham, et al., 1995; Terezow, et al., 2008)

  • Range territory size
    11.5 to 86.7 m^2

Home Range

Despite being territorial, tuataras typically live in close proximity to each other. Males become aggressive when other male tuataras enter their territory. Females will also become aggressive towards other females, but often permit males into their territory. Territory sizes are 11.5 to 86.7 m^2. Female territories are typically half the size of males' and in some cases overlapping territories can occur between sexes. (Gillingham, et al., 1995; Hall, 2007; Lutz, 2005; Terezow, et al., 2008; Walls, 1983)

Communication and Perception

The pupils of the tuatara readily expand and contract to help them see diurnally and at night. Although they have no external ears, they are still able to hear. They are also able to use touch, smell, and taste to perceive their environment. (Lutz, 2005; Naskrecki, 2011; O'Shea and Halliday, 2002)

Tuataras become territorial at about 6 months of age. Males often inflate their bodies, chase off rivals, head bob, gape their mouth, and raise their crests in order to defend their territories. During breeding season males may croak, which is used as a mating call to alert females to their presence. (Gillingham, et al., 1995; Lutz, 2005)

Food Habits

Tuataras are carnivorous and will eat whatever they can catch. They often prey on beetles, worms, lizards, and other tuataras. They prefer to eat wetas (Deincrida rugosa), an insect species that is endemic to New Zealand. Occasionally, tuataras will eat sea bird eggs located in borrows close to their territories. (Hall, 2007; Mitchell, et al., 2008; Naskrecki, 2011; New, 2008)

  • Animal Foods
  • birds
  • reptiles
  • eggs
  • insects
  • terrestrial worms

Predation

Sea bird species that inhabit North Brother Island sometimes attack tuataras, often for territorial reasons. However, swamp harriers (Circus approximans) and New Zealand falcons (Falco novaezeelandiae) are known to catch and consume younger tuataras. Invasive species like rats also predate on tuataras. Young tuataras are diurnal, which, along with their faster speed, helps them avoid being prey to older members of their species. Tuataras may also drop and regenerate their tails in order to escape predation. (Ching, 1986; Lutz, 2005; Meads, 1990; Seligmann, et al., 2008; Terezow, et al., 2008)

  • Anti-predator Adaptations
  • cryptic

Ecosystem Roles

Tuataras prey mostly on invertebrates. As tuataras and sea birds may live in close proximity, tuataras occasionally steal eggs from the birds. The main predators of tuataras include birds (Falco novaezeelandiae and Circus approximans), dogs, and rats. A species of tick (Amblyomma sphenodonti) has been documented as an external parasite of this species. As the specific epithet of this tick indicates, it is only found on tuataras. (Lutz, 2005; Ramstad, et al., 2007; Terezow, et al., 2008)

Commensal/Parasitic Species

Economic Importance for Humans: Positive

Tuataras' unusual physical characteristics and low population numbers attract attention and funding from scientists and conservationists. However, there are no known positive benefits of tuataras to natives of the islands where they are found. Although tuataras are illegal in the pet trade, they have been placed on the black market for thousands of U.S. dollars. (Lutz, 2005; O'Shea and Halliday, 2002; Ramstad, et al., 2007)

  • Positive Impacts
  • research and education

Economic Importance for Humans: Negative

There are no known negative economic effects of Brothers Island tuataras on humans. When threatened or handled, they are capable of delivering a painful bite. (Lutz, 2005; Ramstad, et al., 2007)

  • Negative Impacts
  • injures humans
    • bites or stings

Conservation Status

Human development and introduction of invasive species on North Brother Island appears to have caused the most damage to population numbers in tuataras. Even though population numbers are low and Brothers Island tuataras exhibit a male-oriented sex ratio, long-term survival is probable. Tuataras do not reproduce often, although their long life spans helps with their overall conservation. (Cree, et al., 1991; Hoare, et al., 2006; Lutz, 2005; Nelson, et al., 2002a; Ramstad, et al., 2007)

Brothers Island tuataras are protected by the government of New Zealand. It is unlawful to collect tuataras for pets or kill them for any reason. Due to low population numbers, many organizations have recognized that scientific research on captive tuataras is necessary to conserve this species and keep their genetic diversity as high as possible. Victoria University is actively involved in the long-term survival of the tuatara through studies of captive tuataras individuals. ("Tuatara Recovery Plan 2001-2011", 2001; Lutz, 2005)

Translocation of Brothers Island tuataras has been attempted. However, there is much debate as to whether this is the most useful method for increasing their population size. Nutrients and territory on North Brother Island are limited and too many tuataras might be relocated in the same place. This could potentially harm native and new tuatara populations. If food and territory are not limiting, translocated tuataras appear to adapt well to their new environment. ("Tuatara Recovery Plan 2001-2011", 2001; Nelson, et al., 2002b)

Other Comments

A recent molecular study utilizing microsatellite and mitochondrial DNA concluded that the genus Sphenodon contains only one species, and that Brothers Island tuataras represent a geographic variant of this more broadly distributed species. Despite this study, many researchers and government agencies continue to recognize Brothers Island tuataras as a distinct species. (Hay, et al., 2010)

The Maori tribe have few legends based on the Brothers Island tuatara. Of the people that subscribe to these legends, some believe tuataras are blessings while others believe tuataras act as omens. (Naskrecki, 2011; Ramstad, et al., 2007)

Contributors

Amanda Johns (author), Radford University, Karen Powers (editor), Radford University, Kiersten Newtoff (editor), Radford University, Melissa Whistleman (editor), Radford University, Jeremy Wright (editor), University of Michigan-Ann Arbor.

Glossary

Australian

Living in Australia, New Zealand, Tasmania, New Guinea and associated islands.

World Map

acoustic

uses sound to communicate

bilateral symmetry

having body symmetry such that the animal can be divided in one plane into two mirror-image halves. Animals with bilateral symmetry have dorsal and ventral sides, as well as anterior and posterior ends. Synapomorphy of the Bilateria.

carnivore

an animal that mainly eats meat

chaparral

Found in coastal areas between 30 and 40 degrees latitude, in areas with a Mediterranean climate. Vegetation is dominated by stands of dense, spiny shrubs with tough (hard or waxy) evergreen leaves. May be maintained by periodic fire. In South America it includes the scrub ecotone between forest and paramo.

chemical

uses smells or other chemicals to communicate

cryptic

having markings, coloration, shapes, or other features that cause an animal to be camouflaged in its natural environment; being difficult to see or otherwise detect.

ectothermic

animals which must use heat acquired from the environment and behavioral adaptations to regulate body temperature

fertilization

union of egg and spermatozoan

heterothermic

having a body temperature that fluctuates with that of the immediate environment; having no mechanism or a poorly developed mechanism for regulating internal body temperature.

indeterminate growth

Animals with indeterminate growth continue to grow throughout their lives.

insectivore

An animal that eats mainly insects or spiders.

island endemic

animals that live only on an island or set of islands.

iteroparous

offspring are produced in more than one group (litters, clutches, etc.) and across multiple seasons (or other periods hospitable to reproduction). Iteroparous animals must, by definition, survive over multiple seasons (or periodic condition changes).

motile

having the capacity to move from one place to another.

native range

the area in which the animal is naturally found, the region in which it is endemic.

nocturnal

active during the night

oviparous

reproduction in which eggs are released by the female; development of offspring occurs outside the mother's body.

polygynous

having more than one female as a mate at one time

seasonal breeding

breeding is confined to a particular season

sexual

reproduction that includes combining the genetic contribution of two individuals, a male and a female

solitary

lives alone

tactile

uses touch to communicate

temperate

that region of the Earth between 23.5 degrees North and 60 degrees North (between the Tropic of Cancer and the Arctic Circle) and between 23.5 degrees South and 60 degrees South (between the Tropic of Capricorn and the Antarctic Circle).

terrestrial

Living on the ground.

territorial

defends an area within the home range, occupied by a single animals or group of animals of the same species and held through overt defense, display, or advertisement

visual

uses sight to communicate

References

New Zealand Department of Conservation. Tuatara Recovery Plan 2001-2011. Threatened Species Recovery Plan 47. Wellington, New Zealand: New Zealand Department of Conservation. 2001.

Ching, R. 1986. New Zealand Birds: An Artist's Field Studies. Cornell University: Reed Methuen.

Cree, A. 1994. Low annual reproductive output in female reptiles from New Zealand. New Zealand Journal of Zoology, 21/4: 351-372.

Cree, A. 2002. Tuatara. Pp. 210-211 in T Halliday, K Adler, eds. The New Encyclopedia of Reptiles and Amphibians. Oxford, UK: Oxford University Press.

Cree, A., C. Daugherty, S. Schafer, D. Brown. 1991. Nesting and clutch size of tuatara (Sphenodon guntheri) on North Brother Island, Cook Strait. Tuatara, 31/1: 9-16.

Gillingham, J., C. Carmichael, T. Miller. 1995. Social behavior of the tuatara, Sphenodon punctatus. Herpetological Monographs, 9/1: 5-16.

Hall, D. 2007. The Ultimate Guide to Snakes and Reptiles. Edison, New Jersey: Chartwell Books, Inc.

Hay, J., S. Sarre, D. Lambert, F. Allendorf, C. Daugherty. 2010. Genetic diversity and taxonomy: a reassessment of species designation in tuatara (Sphenodon: Reptilia). Conservation Genetics, 11: 1063-1081.

Hemphill, K. 2012. DK Eyewitness Travel Guide: New Zealand. Penguin.

Hoare, J., S. Pledger, S. Keall, N. Nelson, N. Mitchell, C. Daugherty. 2006. Conservation implications of a long-term decline in body condition of the Brothers Island tuatara (Sphenodon guntheri). Animal Conservation, 9/4: 456-462.

Lutz, D. 2005. Tuatara: A Living Fossil. Salem, OR: DIMI Press.

Meads, M. 1990. Forgotten Fauna: The Rare, Endangered, and Protected Invertebrates of New Zealand. University of California: DSIR Pub.

Mitchell, N., M. Kearney, N. Nelson, W. Porter. 2008. Predicting the fate of a living fossil: how will global warming affect sex determination and hatching phenology in tuatara?. The Royal Society, 275/1648: 2185-2193.

Mitchell, N., N. Nelson, A. Cree, S. Pledger, S. Keall, C. Daugherty. 2006. Support for a rare pattern of temperature-dependent sex determination in archaic reptiles: evidence from two species of tuatara (Sphenodon). Frontiers in Biology, 3/9: doi:10.1186/1742-9994-3-9.

Naskrecki, P. 2011. Relics: Travels in Nature's Time Machine. Chicago and London: The University of Chicago Press.

Nelson, N., S. Keall, D. Brown, C. Daugherty. 2002. Establishing a new wild population of tuatara (Sphenodon guntheri). Conservation Biology, 16/4: 887-894.

Nelson, N., S. Keall, S. Pledger, C. Daugherty. 2002. Male-biased sex ratio in a small tuatara population. Journal of Biogeography, 29/5-6: 633-640.

Nelson, N., M. Thompson, S. Pledger, S. Keall, C. Daugherty. 2006. Performance of juvenile tuatara depends on age, clutch, and incubation regime. Journal of Herpetology, 40/3: 399-403.

Nelson, N., J. Moore, S. Pillai, S. Keall. 2010. Thermosensitive period for sex determination in the tuatara. Symposium: Reptile Reproduction, 5/2: 324-329.

New, T. 2008. Insect Conservation and Islands. Springer.

Newman, D., P. Watson, I. McFadden. 1994. Egg production by tuatara on Lady Alice and Stephens Island, New Zealand. New Zealand Journal of Zoology, 21/4: 387-398.

O'Shea, M., T. Halliday. 2002. Reptiles and Amphibians. Pennsylvania State University: Dk Pub.

Pope, C. 1956. The Reptile World. London: Routledge & Kegan Paul Ltd.

Ramstad, K., N. Nelson, G. Paine, D. Beech, A. Paul, P. Paul, F. Allendorf, C. Daughtery. 2007. Species and cultural conservation in New Zealand: Maori traditional ecological knowledge of tuatara. Conservation Biology, 21/2: 455-464.

Seligmann, H., J. Moravec, Y. Werner. 2008. Morphological, functional and evolutionary aspects of tail autotomy and regeneration in the ‘living fossil’ Sphenodon (Reptilia: Rhynchocephalia). Biological Journal of the Linnean Society, 93/4: 721-743.

Terezow, M., N. Nelson, T. Markwell. 2008. Circadian emergence and movement of captive juvenile tuatara (Sphenodon spp.). New Zealand Journal of Zoology, 35/3: 205-216.

Thompson, M., C. Daughtery, A. Cree, D. French, J. Gillingham, R. Barwick. 1992. Status and longevity of the tuatara, Sphenodon guntheri, and Duvaucel's gecko, Hoplodactylus duvaucelii, on North Brother Island, New Zealand. Journal of the Royal Society of New Zealand, 22/2: 123-130.

Walls, G. 1983. Activity of the tuatara and its relationships to weather conditions on Stephens Island, Cook Strait, with observations on geckos and invertebrates. New Zealand Journal of Zoology, 10/3: 309-318.

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