Galapagose Tortoise Fact Sheet. August, 2003.

Fact Summary
Taxonomy and Nomenclature
Distribution and Habitat
Physical Characteristics
Behavior and Ecology
Diet and Feeding
Reproduction and Development
Diseases and Pathology
Captivity
Conservation & Population Status
Web Resources
Bibliography

TAXONOMY & NOMENCLATURE
(Auffenberg, 1974)(Caccone et al., 1999)(Caccone et al., 2002)
(Ernst & Barbour, 1989)(IUCN, 2002)(King & Burke, 1989)(Pritchard, 1996)
(Van Denburgh, 1914)(Welch, 1994)(Zug, 1997)

Describer (Date): Quoy and Gaimard, 1824 (Testudo nigra)

Kingdom: Animalia
    Phylum: Chordata
        Class: Reptilia
             Order: Testudines
                Suborder: Cryptodira
                    Family: Testudinidae
                           Genus: Geochelone
                                  Species: nigra
                                        Subspecies: (IUCN, 2002)(King & Burke, 1989)(Pritchard, 1996)

	G. n. abingdoni -Pinta (Abingdon) Island (extinct in the wild, 1 captive)
	G. n. becki -Volcan Wolf and vicinity, north Isabela (Albemarle) Island
	G. n. chathamensis -San Cristobal (Chatham) Island
	G. n. darwini -San Salvador (James or Santiago)) Island
	G. n. ephippium -Pinzon (Duncan) Island
	G. n. guntheri -Sierra Negra area of SE Isabela (Albemarle) Is.
	G. n. hoodensis -Espanola (Hood) Island
	G. n. microphyes -Volcan Darwin and vicinity, N central Isabela Is.
	G. n. nigra -southwest Isabela (Albemarle) Island (extinct)
	G. n. porteri -Santa Cruz (Indefatigable) Island
	G. n. phantastica -Fernandina (Narborough) Island (extinct, see below)
	G. n. vandenburghi -Volcan Alcedo and vicinity, central Isabela Is.
	G. n. vicina -Cerro Azul and vicinity, southern Isabela Is.

Taxonomy

Notes on species: Some researchers prefer to use Geochelone elephantopus (rather than G. nigra) as the species name for all Galapagos tortoises (Zug, 1997). Others wish to elevate each subspecies to full species level (Ernst & Barbour, 1989).
Type Specimens - G. n. nigra vs. G. n. elephantopus:
- The type specimen upon which the original description of Testudo nigra was made was (a) young, with a carapace of only 10.5" long (b) missing exact locality information (c) poorly preserved.
- The type specimen upon which T. elephantopus was described was (a) missing exact locality information (b) described too generally to be able to determine its subspecies (c) possibly a young female (d) lost after being donated to a museum.
Notes on subspecies:

Mitochondrial DNA studies reveal little differentiation between the four subspecies from southern Isabela Island (microphyes, vandenburghi, guntheri, and vicina), and little differentiation between guntheri and vicina (Caccone, 1999).
MtDNA evidence shows that there are three genetically distinct populations on Santa Cruz island (G. n. porteri), and more than one lineage from the Volcan Wolf area of Isabela Island (G. n. becki) (Caccone, 2002).
G.n.nigra is a synonym of G.n.galapagoensis; G.n.porteri is a synonym of G.n.nigrita.
G.n.phantastica is based on only a single specimen collected in 1906; taxonomic status is questionable.
G.n. abingdoni is represented by a single individual, named Lonesome George. Only three other individuals are known, museum specimens collected in 1906. Closest living relatives are G. n. chathamensis and G. n. hoodensis from Espanola and San Cristobal Islands, 300 km away.

Common Names

Galapagos tortoise, giant Galapagos tortoise, tortuga gigante de los Galapagos

Phylogeny and Biogeography (Auffenberg, 1974)(Caccone et al., 1999) (Caccone et al., 2002)

Testudinidae evolved from a primitive emydid group in the Late Cretaceous. By the Middle Eocene, representatives existed on all major continents except Australia and South America.
Closest living relative, although not a direct ancestor, is the small Chaco tortoise, Geochelone chilensis, from South America.
Split off from this lineage 6 - 12 million years ago, before the oldest Galapagos island was formed.
Arrived in the Galapagos archipelago 2-3 million years ago by drifting from South America; evolved to large size before leaving the mainland.
Moved from island to island by drifting, and by relocation by seafaring people from the 17th - 19th centuries.
Espanola and San Cristobal, the oldest islands, were colonized first; this was followed by several migration events to and between other islands.

DISTRIBUTION & HABITAT
(Fritts, 1984)(Swingland, 1989)(Van Denburgh, 1914)

Distribution

Found only on Galapagos Islands, west of Ecuador. See subspecies list above for distribution of individual subspecies. Click on map to see a larger image.
		Tortoise distribution on the Galapagos Islands

Habitat

Saddleback shaped carapace populations: dry, low elevation, limited food and other resources (carapace shape allows tortoises to stretch neck upwards and reach food higher off the ground); most often grazers.
Domed carapace populations: more moist, higher elevations, cooler temperatures, food sources closer to the ground; most often browsers.
Observations of seasonal migrations between drier, low elevations areas to more moist areas at higher elevations (up to 2,000 ft) are discussed in Van Denburgh, 1914.

PHYSICAL CHARACTERISTICS
(Fritz, 1984)(Van Denburgh, 1914)

Body Weight: males = 600 - 700 lbs (272 - 317 kg); females = 300 - 400 lbs (136 - 181 kg)
Body Length: Up to approximately 1.8 m (6 ft), males

General

Large bony plates on carapace; shell and skin black; large, stumpy extremities with dry, scaly skin; 5 front claws, 4 on back; beaked, toothless jaw.

Morphological differences between populations (subspecies) were noted by Captain Porter (1812-1814 ship's journal), well before Darwin visited the Galapagos in 1835.

Large amount of individual variation in size and shape seen in all subspecies

Main morphological types

Saddle-shaped, flat carapace, long neck, larger distance between plastron and front of the carapace, which is angled upwards, smaller in overall size, yellowish color on lower mandible and throat.
Domed carapace with taller profile, shorter neck and limbs, front of carapace not as steeply angled, larger body size
Intermediate between saddle and dome shape

Examples of the dome and saddle-shaped shells.

Tortoise skin.

Sexual Dimorphism (Van Denburgh, 1914)

Domed: do not exhibit much sexual dimorphism.
Intermediates: males - high, angled anterior opening, which makes shell look flatter; females - domed, with low anterior opening
Saddle: males - anterior opening higher than that of intermediates (sometimes higher than mid-dorsal shell) and narrow medially; females have same general shape, but less pronounced than in males.
Generally, the plastron in the male is more concave, shorter and has thickened knobs at the posterior margin. Males are usually larger than females.

BEHAVIOR & ECOLOGY
(Darwin, 1989)(Hayes et al., 1988)(MacFarland, 1972)(MacFarland & Reeder, 1974)
(Schafer & Krekorian, 1983)(Swingland, 1989)(Van Denburgh, 1914)

Activity Cycle

Daily activity pattern (MacFarland, 1972)
- Wake up at 7:00-8:00 am
- Most of the day spent foraging
- Rest/sleep starting around 4:00-5:00 pm; remain until morning.
- Often rests half submerged in mud or water, or under thick brush.
Sleep during the day out in the open with limbs extended. Day time rest period also spent in the shade or wallowing in the mud. Cooler evening naps are spent with limb tucked in.
Up to 16 hours a day spent napping.
Most traveling is done in the early morning and the late afternoon.
Retire early, and generally stay in one spot after sundown; have been observed traveling to water holes at night.
Often use established trails from higher feeding areas down to water
Seasonal migrations between the dry coast and the moist areas at higher elevation related to rainfall

Aggression

Demonstrated through dominance displays
Mostly between males, rarely between male/female or two females

Communication

Displays

Dominance Displays:

Males compete with each other for females by facing each other with open mouths, standing tall, and stretching their heads high.
May include biting one another on the head.
The highest head, rather than the largest size, wins. The "loser" retreats in submission.

Defensive Behavior:
- Defensive posture differs subspecifically. When tapped on the anterior end of the shell, G. n. vandenburghi withdraws the legs (already retracted in defense), lifting the posterior end, protecting the anterior end. Head bobbing was observed in 1/3 of the tortoises during a post-defense relaxation period (Hayes et al, 1988).
- Submission: withdrawal of limbs and head, lower body, hiss, retreat

Vocalization

Males vocalize during copulation; they "bellow like bulls" or make "rhythmical groans"
Males and females vocalize during aggressive encounters
Groaning while righting themselves if upside down; possibly to communicate discomfort

Locomotion

Do not swim well, but may drift for long periods of time, carried by ocean current. Float on water, stretching head upwards so they can breath.
Clocked by Darwin at 60 yards/10 minutes (=0.2 mi/hour or 0.3 km/hr); can cover several miles in a day.
Can right themselves if turned upside down onto their backs

Interspecies Interaction

Various species of passerine birds fly around tortoises, eating flying insects that buzz around their heads.
Mutualistic relationship with Darwin's finches observed by MacFarland and Reeder (1974)

Small group of finches lands in front of or on the back of a tortoise
They begin to hop, in exaggerated way, facing head of tortoise.
The tortoise rises up, lifts its head, stretching its neck, and extending its legs
The finches landed on different areas of the tortoise and begin picking off ticks that are hidden in the folds of the skin.
Most commone areas that are cleaned by the finches: rear legs, cloacal opening, neck, and skin between plastron and carapace.

DIET & FEEDING
(MacFarland, 1972)(Swingland, 1989)(Van Denburgh, 1914)

Can survive without food or water for at least a year
Drink through their mouths; drink large quantities of water at a given time, and store it in their bladders and the "root of the neck", which may be the pericardium.
Water obtained from water holes, springs, rock depressions after a rain, by licking dew off of rock surfaces, or by eating Opuntia cactus
Feed on cactus, leaves, grass, berries (guayavita), and lichen. Cactus is the preferred food.
Also observed eating berries of the manzanillo tree (different from guayavita?) which is poisonous to humans, and stinging nettles.
As with all ectotherms, the speed of digestion is influenced by the ambient temperature. Higher temperature = higher metabolism, quicker digestion.

REPRODUCTION & DEVELOPMENT
(Darwin, 1898)(MacFarland et al., 1974)(Rostal et al., 1998)(Swingland, 1989)
Courtship

Mating occurs December - August, peaking February - June.
Mating generally coincides with the rainy season
Male sniffs the air when looking for a female to mate with
Male follows the female, who almost always retreats. Male nips at her heels and rams her causing her to get into a position which allows him to mate (lowers her body, retracts her legs).
The male's plastron is concave, which allows for easier mounting of the female.

Gestation: 120 - 240 days

Nesting

Egg laying season is June - December, peaking July - November.
Generally coincides with the dry season.
Females migrate from the higher elevation areas, where resources are more abundant, to the coastal areas to lay their eggs.
In sandy areas the female digs a hole and urinates to make the sand wet so it won't collapse on the eggs. She deposits the eggs in a pile and spreads them out into a single layer. Lastly she covers them with six inches of sand, which often dries into a hard cover.
MacFarland (1972) observed this to take 5 hours for one Santa Cruz female. It took 15 minutes for her to lay 9 eggs.
In rocky areas, the eggs are deposited randomly into cracks.

Life Stages

Eggs

Average clutch size during a 1969-1971 study was 9.3/nest for G. n. porteri and 5.1/nest for G. n. ephippium. Approximately 78% of the eggs of both sub species hatched (MacFarland et al., 1974).
Clutch size range for species: 8-17; varies among individuals, subspecies, and annually.
Interclutch interval: 1-2 weeks
Incubation takes 3-8 months and is influenced by ambient temperature.

Hatchlings: Hatching and emergence late December to early April.

Young

Shells striated when young; loss of this character as adults differs among subspecies
Young retain "their specific characters" until nearly adult. Subspecies are indistinguishable at this time. All have domed carapaces, anterior not sharply angled.
Shorter extremities than adults
Young grow at a more rapid rate than adults.

Adults

Sexual maturity reached at 20-25 years in captivity; possibly up to 40 years in the wild.
Carapace grows by increasing diameter of each plate along its margins.

Longevity

It is difficult or impossible to age tortoises; rings on scutes (boney plates on carapace) vary with climatic conditions.
Estimated to live up to 150 years (MacFarland, 1972).

Mortality

Mortality rate in hatchlings and young animals varies depending on environmental conditions
Young tortoises may die by falling into cracks, being crushed by falling rock, or being exposed to excessive heat stress.
Mortality of older tortoises often due to a long fall.

Captive Breeding

See Conservation
Results from reproduction studies of captive tortoises at Gladys Porter Zoo, Brownsville, TX (Rostal et al., 1998) show:

Males and females showed seasonal, rather than year round, reproductive cycle.
Corresponding changes in physiology included:

Males: prior to mating- rise in testosterone level, maturation of gonads, and spermatogenesis. No changes in serum calcium levels were observed.
Females: Pre-mating rise in estradiol, increased serum calcium levels, ovarian follicular maturation, and vitellogenesis (ovarian development). Mating period, prior to ovulation- rise in testosterone level, maturation of ovaries, increased receptivity of female. Mating/nesting period- sharp rise in progesterone coinciding with ovulation.

Separation of a male (thought to be essential for successful breeding) did not show any changes in reproductive physiology.

DISEASES AND PATHOLOGY
(CGFG,2003)(Shaw, 1967)(Van Denburgh, 1914)

22 G. n. porteri deaths, investigated in 1999, were caused by bacterial septicemia
Susceptible to respiratory illnesses in captivity
Ectoparasites: ticks attach wherever skin is thin, such as joints

CAPTIVITY
(CDFG, 2003)(Shaw, 1967)(Zoonooz 1928, 1978, 1997)

1928: San Diego Zoo received its first Galapagos tortoises, collected by Dr. Townsend on Isabela island. San Diego Zoo and several others began breeding programs (instigated by Dr. Townsend) as an attempt to stave off extinction.
1930's: A second group (G. n. hoodensis) was received from Espanola Island.
1920's - 1950's:: Most attempts to incubate eggs were unsuccessful.
1959: First successful hatching at San Diego Zoo.
1977: San Diego Zoo returns its only G. n. hoodensis to the Galapagos rearing station. It is one of only 13 left in existence.
Present: Some of the original 1928 tortoises are still alive and well. Based on age estimates upon their arrival, these individuals could be over 100 years old.

CONSERVATION AND POPULATION STATUS
(Caccone, 1999)(Caccone et al, 2002)(CDFG website, 2003)
(Ciofi, 2002)(GCT website, 2003)(MacFarland et al., 1974)(Swingland, 1989)
(Van Denburgh, 1914)

Population Status

Current population estimates, from GCT website, 2003:
- Santiago Island: 800 (G. n. darwini)
- Pinzon: 300 (G. n. ephippium)
- Santa Cruz: 3000 (G. n. porteri)
- San Cristobal: 700 (G. n. chathamensis)
- Española:120 (G. n. hoodensis)
- Isabela Island
  - Volcan Cerro Azul: 700 (C. n. vicina)
  - Sierra Negra: 500 (G. n. guntheri)
  - Volcan Alcedo: 5000 (G. n. vandenburghi)
  - Volcan Darwin: 1000 (G. n. microphyes)
  - Volcan Wolf: 2000 (G. n. becki)
- Pinta: extinct in the wild. One individual in captivity. (G. n. abingdoni)
ISIS captive population (link requires Internet Explorer)

Conservation (CDFG, 2001)(CDFG, 2003)(Ciofi, 2002)

1936: Ecuadorian government lists the giant tortoise as a protected species
1959: Galapagos National Park and the Charles Darwin Foundation created
1965: Tortoise Rearing Program established on the Galapagos Islands to breed and restore populations to the wild, and to control harmful exotic species (goats, rats, etc.). First project was to save Pinzon Island populations from the black rat. Most of the funding came from San Diego Zoological Society.
1960's/ 1970's:

G. n. abingdoni (1, 1972) and G. n. hoodensis (14, late 1960's) were so rare that they were removed from the wild for their protection.
1977: San Diego Zoo returned a male G.n. hoodensis to the captive colony, which was composed of 2 males and 12 females.

1999: mtDNA studies showing G. n. abingdoni's close relationship to populations from Espanola and San Cristobal island; may make breeding attempts more successful in the future. Previously, breeding was done with Isabela Island populations (Caccone, et al., 1999).
Present:
- Attempts to breed Lonesome George (G. n. abingdoni) have been unsuccessful, but over 1,000 G.n. hoodensis have been bred and introduced to Espanola Island (1999 annual report).
- Approx. 200 G. n. ephippium have been reintroduced to Pinzon Island (Ciofi, 2002).
- Overall, 2500 individuals have been reintroduced to the islands (CDFG, 2001)
IUCN Status: Species vulnerable. Individual subspecies are listed as vulnerable, endangered, critically endangered, or extinct.
CITES Status: Appendix I

Threats to survival

Historical
- Prior to the 20th century, up to an estimated 200,000 were collected by whalers and other seafarers as a source of food. Based on ships' logs, 13,013 tortoises were collected during 189 visits between 1831 and 1838. (This number only includes ships whose logs were available.) Considering that collecting had occurred since the 17th century, this represents only a small fraction of actual captures.
- Settlers began moving to the islands in the 1800's; they killed tortoises for meat and oil and destroyed their habitat when clearing for pasture and fences.
- In 1897, one observer found 150 skeletons by a water hole, and 100 more half a mile away. Also observed at a nearby settlement: 1200 gallons of tortoise oil, representing 400 to 1200 large tortoises (1-3 gallons per tortoise), Van Denburgh (1914).
- Non-endemic mammals were introduced, which preyed on eggs and young, and competed for resources (goats, rats, dogs, donkeys, pigs, cats).
- Scientific collecting expeditions took 661 tortoises between 1888 and 1930
Present
- Introduced mammals are still a threat
- The only endemic predator is the Galapagos hawk, which preys on eggs and hatchlings
- Poaching and habitat destruction by humans continues

Important Web Resources:

Restoring the Tortoise Dynasty, prepared by the Charles Darwin Foundation for the Galapagos
Charles Darwin's Journal from the Voyage of the H.M.S. Beagle (Galapagos Islands), 11th edition, 1913.
Galapagos Conservation Trust
Galapagos National Park, Ecuador.
Galapagos Islands Flora
Galapagos Islands Geology

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