Tortoises are personal pets that have gained immense popularity around the world in recent years. And as evidenced by the proliferation of books and websites catering to the subject of captive tortoise maintenance, keepers of tortoises are constantly seeking information about providing their pets with optimal conditions.Many species adapt well to captivity, but pet tortoises are very much wild animals. Knowledge about their wild counterparts, therefore, may help tortoise keepers go a long way in satisfying the needs of their pet tortoises. The purpose of this article is to discuss aspects of the biology of wild tortoises – including evolutionary history, life history traits, physiological ecology, and social behaviors and communication – that can help keepers of tortoises provide a better existence for both captive and wild tortoises. In my fourth post, I discuss social behaviors and communication in tortoises.
An understanding of wild tortoises, such as this wild adult male Agassiz’s desert tortoise, can give keepers of captive tortoises great insight into the lives of their pets. Photo by Michael Tuma.
Social Behaviors & Communication
Perhaps one of the most interesting aspects of tortoises is the complexity of their social and communication behaviors. Though wild tortoises are predominantly solitary animals, they interact frequently with members of their own species, display a variety of methods of communicating, and exhibit social structures within populations (Douglass 1976; Guyer et al. 2012). During social and communication behaviors, tortoises use a number of senses, including visual, olfactory, auditory, and tactile. They are capable of seeing color, have incredibly good senses of smell, emit and hear vocalizations, and are very sensitive to touch (Auffenberg 1977). Human keepers of captive tortoises can better understand and more deeply appreciate their pets with knowledge of sensory processes, modes of communication, and repertoire of social behaviors in wild tortoises.
Tortoises are very social animals, and use a variety of behaviors and senses in their communications with each other. Photo by Aaron Logan.
Wild tortoises, particularly adults, are very social animals. They display a variety of complex social interactions, especially during male-male combat and male-female courtship. As well, individual tortoises exhibit a range of personality types from very shy to inquisitive to aggressive. Their varying personalities, coupled with their interactions with each other, help to define dominance hierarchies and social structure within tortoise populations. Being long-lived animals, they really get to know and have relationships with other tortoises within their locality. They remember the outcomes of prior interactions, and learn to avoid or respond positively to tortoises that they have previously interacted with (Berry 1986). For example, a male tortoise that has previously lost a fight with another male may flee or hide in a defensive posture if he sees or smells his dominant rival.
Courtship behaviors include some of the most complex social behaviors exhibited by tortoises. Communications during courtship begin with male fixation and head-bobbing signals. Fixation is easily recognized by the posture of the male as he extends his neck toward the female, eyeing her with intent. His goal is to convince the female, through persuasion or coercion, to submit to his advances. He will trail her if she is on the move, using a combination of head-bobbing and fixation to send the signal that he’s interested in copulating. He may begin circling her, occasionally biting and ramming her shell to get her to submit. Once the male has immobilized the female, he then mounts her. During mounting and subsequent mating, the male may exhibit mouth-gaping, emit grunt-like vocalizations, and bump his shell against the female to persuade her to submit to copulation (Auffenberg 1977; Ruby and Niblick 1994).
Another complex social behavior exhibited by tortoises is male-male combat, which also includes signals such as head-bobbing, shell ramming, and biting. Adult male tortoises of many species engage in one-on-one combat to establish dominance within local social hierarchies and to defend territories in an effort to gain access to females. In some species, the importance of male-male combat in securing territories and mates has led to the evolution of specialized body parts. Species such as the North American Gopherus tortoises, the Madagascan ploughshare tortoise, and the southern African angulate tortoise exhibit elongated, variably curved gular scutes, or a gular ‘horn,’ that is used to overturn opponents during fights (Mann et al. 2006). Male-male combat behaviors, as well as male-female courtship behaviors, may occur at any time during the activity season, but are particularly common during seasons when blood testosterone levels in males are high (Rostal et al. 1994).
In some tortoise species, such as North American Gopherus tortoises, male-male combat is a prominent feature of mating systems. Photo by Andrea Westmoreland.
Outside of combat and courtship behaviors, tortoises exhibit a number of other social behaviors and communications that are practiced by juveniles and adults alike. These behaviors include easily-recognized signals such as head-bobbing and nose touching, but also more subtle behaviors, such as body posture and breathing patterns. While head-bobbing is most often practiced by adult tortoises as a precursor to courtship and combat behaviors, less stylized head-bobbing signals may be used by tortoises of any age during less formal social interactions. Head-bobbing in these instances is typically less flamboyant and shorter in duration. Tortoises also communicate with each other using nose touching, which generally indicates curiosity, and is used as a method of introduction during initial meetings. Tortoises have remarkably sensitive noses, with lots of nerve endings for tactile senses, and a well-developed sense of smell. When engaging in nose touching, tortoises investigate each other as a means to determine species, sex, and temperament. Tortoises with outgoing personalities readily practice this behavior, whereas a shy tortoise may interpret nose touching as a sign of aggression. Tortoises communicate with each other with a variety of postural signals, which involve their heads, limbs, and shells. Tortoises communicate aggression, dominance, or curiosity with postures that elevate their heads or bodies; fear with postures that include withdrawing their head and limbs into their shells or turning their bodies in a retreating manner; and comfort or nonaggression with a relaxed pose that includes relaxed limbs and a partially extended and/or slightly elevated head. These postures are often accompanied by patterns of breathing that reinforce the communication signals. For example, a tortoise exhibiting fear may quickly expel air from its lungs when retreating into its shell, creating a hissing noise. A tortoise communicating comfort in a relaxed pose will often take short, quick breaths accompanied with slight head bobs with each breath.
This red-footed tortoise is displaying a relaxed, nonaggressive pose, as well a curiosity about the photographer. Photo by Postdlf.
Keepers of pet tortoises can gain a great understanding of their pets by recognizing the sociality of wild tortoises and the manners in which they communicate. Tortoise keepers may also be able to provide safer environments for their pets, recognize signals that convey personality, mood, or health, and even communicate with their tortoises with this knowledge. Though tortoises are social when they meet in the wild, keepers of captive tortoises should also understand that their pets may be kept singly without ever ‘feeling’ lonely. However, keepers that maintain tortoises in groups should be especially aware of aggressive behaviors, whether they are male-male, or male-female, that may occur during courtship or combat. Overly-aggressive behaviors or overexposure to prolonged aggressive interactions can result in fairly serious injuries (Chancellor et al. 2003).
With an understanding of how wild tortoises communicate with each other, keepers of pet tortoise may be able to interpret their social signals and personalities, and communicate nonaggression signals to them. Keepers should use nonthreatening movements and handling techniques with shy tortoises. For example, tapping a tortoise on top of its shell or turning it upside down would be interpreted by the tortoise as aggression, especially by a shy animal. With sufficient observation and practice, a tortoise keeper may be able to communicate comfort or nonaggression to their animals using signals that tortoises understand. To simulate nose touching, keepers can (using their fingers) gently touch their tortoise on the shell, limbs, or head in a manner that communicates curiosity to their pets. Head-bobbing with short, rhythmic bobs to communicate a relaxed state can be accomplished by a tortoise keeper with the use of their thumb, finger, closed fist, or even their own head. When communicating with their pets, tortoise keepers should ‘think’ like a tortoise.
Keepers of tortoises can communicate nonaggression with their pets using a variety of methods. Photo by D.R. Trotsky.
Literature Cited
Auffenberg, W. 1977. Display behavior in tortoises. American Zoologist 17(1):241–250.
Berry, K. H. 1986. Desert tortoise (Gopherus agassizii) relocation—implications of social behavior and movements. Herpetologica 42:113–125.
Chancellor, S. D. Senneke, and C. Tabaka. 2003. Combat injuries in Russian tortoises (Testudo horsfieldii). http://www.chelonia.org/articles/russiantortoisecombat.htm. World Chelonian Trust.
Douglass, J. 1976. The mating system of the gopher tortoise, Gopherus polyphemus, in southern Florida. MS Thesis, University of South Florida, Tampa.
Guyer, C., V. M. Johnson, and S. M. Hermann. 2012. Effects of population density on patterns of movement and behavior of gopher tortoises (Gopherus polyphemus). Herpetological Monographs 26:122–134.
Mann, G. K. H., M. J. O’Riain, and M. D. Hofmeyr. 2006. Shaping up to fight: sexual selection influences body shape and size in the fighting tortoise (Chersina angulata). Journal of Zoology 269:373–379.
Rostal, D. C., V. A. Lance, J. S. Grumbles, and A. C. Alberts. 1994. Seasonal reproductive cycle of the desert tortoise (Gopherus agassizii) in the eastern Mojave Desert. Herpetological Monographs 8:72–82.
Ruby, D. E. and H. A. Niblick. 1994. A behavioral inventory of the desert tortoise: Development of an ethogram. Herpetological Monographs 8:88–102.