Galapagos Giant Tortoises (Chelonoidis spp.) Fact Sheet: Reproduction & Development

Male mating behavior (Schafer 1982; Bonin et al. 2006, and as noted)

• Male approaches female
• Sometimes chases her
• May nip one of her limbs
• May sniff rear part of her shell or cloacal region (“nosing”)
• Likely to assess female’s reproductive condition
• Mounts female, with forelegs propped up on the front of her shell
• Large males dwarf small females
• Often produces loud bellows while thrusting (Jackson and Awbrey 1978)
• Courtship may last a long time, but copulation said to be brief

Female mating behavior

• Males often approach when females are resting or lying still (Schafer 1982)
• Females generally unresponsive to male courtship
• Isolated reports of the female lifting the rear part of her body (cited by Schafer (1982))
• Females typically lie still when permitting mating (Schafer 1982)
• May move away
• May rotate body or push male away to avoid/dislodge mating attempts
• Evidence of female mate choice in some populations (Garrick et al. 2014)

Breeding cycle

• Typically begin reproducing at approximately 20-25 years of age (Milinkovitch et al. 2012; Cayot et al. 2016)
• Reptiles typically reproductive throughout their lives (Paré and Lentini 2010)
• Mating typically toward the end of the wet season (Bonin et al. 2006)
• Corresponds with warm seasonal temperatures (Schafer 1982)

Egg description (de Vries 1984; Bonin et al. 2006, except as noted)

• Spherical
• White
• About 50 mm in diameter
• About the size of a tennis ball
• Mass varies by species
• 110-120 g (3.9-4.2 oz) (Linda Cayot, personal communication, 2016)
  

Egg laying

• Females often migrate to lowland sites during breeding season (Swingland 1989)
• Some nest in mountainous or volcanic areas (de Vries 1984)
• Not known if Giant Galápagos Tortoises (GGTs) exhibit nest site fidelity (Jensen et al. 2015)
• 1-4 clutches laid per breeding season (de Vries 1984; Casares et al. 1997)
• Typically June-December
• Eggs can be retained in the female's body for over a year
• May not lay in dry years
• Nest (de Vries 1984)
• Cylindrical
• 30-40 cm (12-16 in) deep
• Female digs nest in sand with hind limbs (de Vries 1984; Swingland 1989; Bonin et al. 2006)
• Takes several hours for female to dig nest
• Urine used to soften the soil, if digging in soil
• Plastron used to press down soil and close the nest
• Eggs then incubated by heat from the sun
• Clutch size
• Saddle-back GGTs: 2-7 eggs
• Domed GGTs: 20-25, or more, eggs
• Clutch size varies (Swingland 1989):
• Among individual females
• Among species
• From year to year
•  Incubation period
• Longer during cool seasonal temperatures (June-August), shorter during warm seasonal tempertures (November-December) (Linda Cayot, personal communication, 2016)
• Varies among species (Elizabeth A. Hunter, personal communication, 2016)
• Wide range reported
• Incubation: 80-100 days (Bonin et al. 2006)
• Incubation: 110-175 days (Galápagos Conservancy 2017)

Hatchlings

• Hatch and emerge December-April (de Vries 1984)
• High rate of hatching success, where nests intact
• Heat and excessive rainfall may trap and kills hatchlings while in the nest
• Thought that hatchlings remain in nest before all emerge at the same time, as a group (Linda Cayot, personal communication, 2016)
• Weigh about 70-90 g (2.5-3.2 oz) (de Vries 1984; Wacho Tapia, unpublished data)
• Shell
• Soft (Standford 2010)
• Flat (Bonin et al. 2006)
• Uniform dark color (Bonin et al. 2006)

• Little published research
• After hatching, young remain in nest for a few weeks before emerging (galapagos.org)
• Remain in lowlands during their early years of life (Standford 2010)
  • Hide in vegetation/rocks and remain inconspicuous
    • Avoid predators
• Grow rapidly (Bonin et al. 2006)
• Begin reproducing at approximately 20-25 years of age (captive animals) (Milinkovitch et al. 2012; Cayot et al. 2016)
  • Generation length: 60 years
• Long-lived
  • Over 100 years (Bonin et al. 2006; Paré and Lentini 2010)
  • Perhaps up to 150 years in managed care (Cayot et al. 2016)

Wild populations

• One of the longest-lived vertebrates (Paré and Lentini 2010)
  • Maximum age often overestimated (Bonin et al. 2006; Orenstein 2012)
• Typical life expectancy not reported

Managed care

• Median life expectancy
  • 49 years (AZA 2023)

Causes of mortality (MacFarland et al. 1974; de Vries 1984; Elizabeth A. Hunter, personal communication, 2016)

• Predators
  • Non-native predators introduced by humans
    • Pigs, dogs, rats, fire ants
      • Prey on eggs and hatchlings/juveniles
    • Also see Threats to Survival
  • Native predators
    • Galápagos hawk
      • Not as abundant as before humans arrived in the islands
        • Pose much less threat to GGTs today
      • Target hatchlings, as they emerge from nest
      • Eat juveniles
• Fall into crevices
• Crushed by falling rocks
• Heat stress
• Respiratory infections
• Malnutrition and starvation in hatchlings/juveniles

Diseases and parasites (non-comprehensive list)

• Widespread nematode presence (Fournié et al. 2015)
  • 80% of individuals in wild populations infected
  • Implications for captive breeding management, release, and relocation
• Animal medical discoveries among GGTs
  • First mast cell tumor ever described for a chelonian was found in a GGT (Santoro et al. 2008)
  • New fungal genus discovered on GGT shells (Sutton et al. 2013)
    • Produces white lesions in keratin between scutes
    • Should be considered in the husbandry and breeding of GGTs in managed care

In 1958, the San Diego Zoo had its first success in hatching Giant Galápagos Tortoise eggs. Here, reptile keeper Jerry Staedeli examines a nest.

Reptile curator Charles Shaw had the insight to provide females with a nesting area made of river-bottom sand instead of dirt. Just two months later, six clutches of eggs were laid!

For years, the San Diego Zoo housed the only breeding colony among zoos, worldwide.

Image credit: © San Diego Zoo Wildlife Alliance. All rights reserved.