Galapagos Giant Tortoises (Chelonoidis spp.) Fact Sheet: Behavior & Ecology

• Active during the day (Bastille-Rousseau et al. 2016)
• Rest about 16 hours per day (Galápagos Conservancy 2017)
• Rest in sun/shade for much of the day (Schafer 1982)
• Immobile at night (Bastille-Rousseau et al. 2016, citing S. Blake unpublished data)
• Sleep-like behaviors (Schafer 1982; Swingland 1989; Hayes et al. 1992)
• Rest plastron on ground
• Relax limbs
• Rest head on plastron or on ground/object
• Close eyes
• Distinct postures may help Giant Galápagos Tortoises (GGTs) thermoregulate
• Warmer hours: head and limbs extended
• Rest in open habitat areas
• Offload heat through limbs
• Cooler hours: head and limbs withdrawn
• Rest near hillsides, vegetation, or facing other tortoises
• Retain heat
• Long periods of inactivity during harsh conditions (Bonin et al. 2006; Orenstein 2012)
• Especially on arid islands

• Wide variation in movement behavior (Bastille-Rousseau et al. 2016)
• Influenced by body size and environmental conditions (e.g., weather)
• Have adapted differently to conditions on each island
• Exhibit different movement strategies (Bastille-Rousseau et al. 2016)
• Mostly resident individuals tend to have smaller home ranges
• Migratory individuals tend to have larger home ranges
• May move over 10 km (6 mi) per year
• Study of four GGT species (Bastille-Rousseau et al. 2016)
• Distance moved per day (for three species): 45-100 m (148-328 ft), on average
• Up to 3,000 m (9843 ft) each month
• Distance moved per day for a fourth species: up to 200 m (656 ft)
• Up to 5,800 m (19,028 ft) each month
• Some individuals seasonally migrate along elevation gradients (Blake et al. 2013; Blake et al. 2015a; Blake et al. 2015b)
• Follow food
• Move to higher elevations in summer and fall (July-October)
• Early in wet season, when new vegetation is easier to digest
• Larger individuals more likely to migrate
• Tend to migrate upslope earlier than smaller individuals
• Trails through vegetation left by GGTs (de Vries 1984; Swingland 1989)
• Created by GGTs reusing the same paths
• From highlands to lowlands
• To water sources
• Have provided easier penetration for humans into dense vegetation
• Woody shrubs may block movements (Gibbs et al. 2014)

• Primary herbivore in the Galápagos (Gibbs et al. 2010)
• Shape ecological communities (Blake et al. 2012; Blake et al. 2015a)
• Selectively feed on plants
• Disperse seeds
• Many kinds of seeds (both native and introduced plants)
• Spread over long distances
• 100 m to over 4 km (330 ft to 2.5 mi) from parent plant
• May play a role in cactus germination (Gibbs et al. 2010; Gibbs et al. 2014)
• Effects unclear
• GGTs helping restore cactus to Española, after detrimental goat grazing
• Trample/flatten plants
• Can affect growth and survival of juvenile cacti (Gibbs et al. 2010)
• Promote nutrient cycling
• Proposed as a tool for island ecosystem restoration (Gibbs et al. 2014)

General

• Mostly solitary (de Vries 1984; Bonin et al. 2006)
• Aggregate around resources (de Vries 1984; Bonin et al. 2006; Sulloway 2009)
  • Food
  • Shade
  • Water sources
    • Wade communally in water or muddy pools, for hours at a time
    • Benefits
      • Aids thermoregulation
        • Cool off or stay warm during cold nights
      • Reduces parasite loads; avoid mosquito bites
• One study reports aggregations at night (Hayes et al. 1992)
  • Possible thermoregulatory benefit

Dominance behaviors

• Exhibit dominance hierarchies (Schafer 1982), though not well-studied (especially in the wild)
  • Compete for food, mates, and resting sites
  • Males typically dominant over females
  • Male-male fights more common than male-female fights
• Establish dominance ranks by stretching necks and comparing neck lengths (Schafer 1982; Orenstein 2012)
  • "He who can stretch his neck highest wins."
  • Observed in both saddleback and domed GGTs
    • Long neck extensions performed by saddlebacks
      • May have evolved in response to more intense competition for resources on more arid islands

Protective behaviors (Hayes et al. 1988; Bonin et al. 2006)

• Raise head
  • To better observe what is approaching
• Lower head
• Withdraw head, legs, and tail
• Hiss, while tucked inside shell
• May abruptly collapse to the ground when sense possible danger (Bonin et al. 2006)
  • Air forced out of lungs makes a blast-like sound
• Defensive stance
  • Withdraw head and front limbs
    • Anterior end low to the ground
  • Rear legs extended
    • Posterior end raised
    • Shell angled towards what is approaching
  • See Figure 1d of Hayes et al. (1988)
  • Often accompanied by hissing
• Some individuals bob their heads up-and-down, as they begin relaxing
• Withdrawal behaviors reported since the early 1700s (Baur 1889)

Agonistic behaviors (Schafer 1982)

• Chasing
• Pushing a conspecific away
• Mouth gaping
  • Some GGTs have yellow in their mouths to make the display more conspicuous
• Biting
  • Usually on an opponent’s head
  • Rarely inflicts a wound
• Extending necks (see General, this box, above)
• Leaning necks against each other
  • Infrequent behavior
• Submissive responses
  • Lowering head
  • Closing mouth
  • Withdrawing head into shell
  • Turning and moving away

Visual communication

• Ritualized neck extension behavior (see Dominance Behaviors, above) (Schafer 1982; Orenstein 2012)
  • Visual way to establish dominance ranks
    • Precludes injury through physical contact
• Head bobbing (Schafer 1982; Swingland 1989)
  • Observed in some GGTs
    • Function or benefit, if any, unknown

 Vocalizations

• Few vocalizations reported
  • Hiss in defense (Hayes et al. 1988)
  • Grunts and bellows by male during mating (Jackson and Awbrey 1978)
• Hearing limited
  • Not well-studied
  • May be similar to other turtles (Jackson and Awbrey 1978)
    • Insensitive to tones above 1 kHz

Olfactory communication

• Male may sniff rear part of female’s shell or cloacal region (“nosing”)
  • Likely to assess a female’s reproductive condition

Tactile communication

• No detailed studies
• Important in mating and agnostic behaviors (see Social Behavior)

Walk (Schafer 1982)

• Slow speed
• Body supported by three legs
• Observed in heavy, adults tortoises and cold tortoises (early in the morning)
• Moderate speed
• Body supported by two, opposite legs
• E.g., left front, right rear

• Take dust baths, perhaps to cool down (Bonin et al. 2006)
• Turn their bodies in powder-like soils
• May also help control parasites

Goats (Gibbs et al. 2014)

• Compete for food with GGTs
  • Opuntia (prickly pear cactus)

Cleaner birds (de Vries 1984; Bonin et al. 2006; galapagos.org)

• Galápagos finches and vermillion flycatchers
  • Remove ticks and seeds from wrinkles from skin
  • GGTs rise up high on legs and extend neck
    • Finches hop around on ground in front of tortoise to elicit this response

Albatross

• GGTs trample/flatten plants while walking, especially when reusing trails (Gibbs et al. 2010)
• Albatross use the open landscape areas that GGTs create as “runways” for flight takeoffs and landings (Elizabeth A. Hunter, personal communication, 2016)

Giant Galápagos Tortoises rest together in the shade.

Image credit: © Adam Nash/Henry Polo at Flickr. All rights reserved. Used with permission from the artist.