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
- Submissive responses
- Lowering head
- Closing mouth
- Withdrawing head into shell
- Turning and moving away