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AMER. ZOOL., 17:241-250 (1977). Display Behavior in Tortoises WALTER AUFFENBERG The Florida State Museum, University of Florida, Gainesville, Florida 32611 SYNOPSIS When compared to lizards or snakes, signals related to warning and threat are not very important in land tortoises. Within social and sexual contexts, tactile and chemical signals seem more important than visual, and certainly than auditor)' ones. Color patterns are rarely, if ever, sexually discriminatory. Seasonal color differences are rare. In general, positional signals are rather limited, chiefly because of the shell. However, shell positional changes are an important part of the visual and tactile signal repertory of all land tortoises. Head movements are also important in several groups. Audible signals are poorly developed. They are largely concerned with courtship and their role is not understood. Chemical signals are pronounced, especially in displays related to sex identification, largely based on scents associated with the cloaca. Tactile displays are important particularly during courtship. They include biting and especially shell ramming by the male. The tail is used as a tactile organ during courtship of some species. INTRODUCTION In spite of the knowledge gained over the last several decades concerning reptile behavior, it is clear that while we may know several thousand species in the preserved state, we are only vaguely familiar with less than a hundred in the behavioral sense. There is no question but that this lack represents a challenge and an opportunity many biologists are finding highly stimulating. In general, the behavior of turtles is poorly known. At present most data are available for land tortoises, but even here our state of knowledge is very primitive. As a result, comparisons are difficult and only broad categorizations are possible. The following, unfortunately, represents the bulk of our knowledge of land tortoise display behavior. SIGNAL REPERTORY Auditory signals Despite early reports of turtle vocalization, little attention was directed to this behavior until recently. This is largely due to the once widespread belief that chelonians were deaf to airborn sound (Pope, 1955). Thus most workers regarded these sounds as being accidental or incidental to other activities. However, it is now clear that many turtle species are actually quite sensitive to airborn sounds, particularly those below 1000 Hz (Wever and Vernon, 1956). Within this frequency range their sensitivity is actually better than that of many lizards and compares favorably with that of the pigeon and guinea pig (Peterson, 1966). While sound production occurs in a wide variety of turtles, it is particularly common in the testudinids. Many tortoise species are known to vocalize, particularly in a courtship context (Table 1). Various species-specific sounds may be produced by the males of some species when following or approaching the female, when mounted, or sometimes when foraging (Campbell, 1967). Campbell and Evans (1967) believed the latter might serve the same function as the contact calls of other vertebrates (Collias, 1960). Campbell (1967) demonstrated that when the sounds are played back the tortoises sometimes exhibit a visual, but not an auditory response. Some species are known to produce sounds during male combat (Table 1). At least two species produce one vocalization during courtship while following or approaching the female and another during mounting (Geochelone elephantopus, DeSola, 1930; Geochelone car- bonaria, Snedigarand Rokosky, 1950; and 241 242 WALTER AUFKENBERG TABLE 1. Vocalization reported in tortoise species. Species Geochelone carbonana Geochelone elegans Context Mounted and courtship Foraging Mounted Geochelone elephanlopus Mounted and Author(s) Remarks (as denliculata) "grunts," "short croaks" "roars and bellows" courtship Geochelone gigantea Geochelone pardalis Mounted Mounted Geochelone radiata Mounted Geochelone travanconca Foraging and Gopherus agassizi resting Mounted Gopherus berlandien Gopherus polyphemus Resting Mounted Mounted Psammobates oculifera Tesludo hermanni Testudo graeca Mounted Mounted Mounted "moans and bellows" "grunts and groans," "husky cry" "rhythmic grunts" Sometimes in choruses in rain; "croaking" "grunting" "moan" "grunts" "grunts" Gopherus agassizi, Campbell and Evans, 1967). No complete analysis of sound production is available for any species, but preliminary work by Campbell and Evans (1967, 1972) shows that the calls range from 500-2500 Hz. While the overlap is not great, studies show that maximum auditory sensitivity for turtles is at about 400-500 Hz (see Adrian, Craik, and Sturdy, 1938 and Campbell and Evans, 1972 for review). While some headway has been made in establishing the species groups in which sounds are produced, and there is now at least some information on energy level and sensitivity, the purpose of these sounds remains unclear. The sound of tortoises is made by the breathing apparatus, except for G. travancorica in which it seems to be produced by the mandible rubbing against the maxillary. Hissing represents another sound category. This common signal in tortoises is believed to be of value in discouraging predation (Mertens, 1946). It is usually produced when the limbs are quickly pulled into the shell. Snedigar and Rokosky, 1950; Grant and DeSola, 1934 Campbell, 1967 Jayakar and Spurway, 1966; Deranyagala, 1939 DeSola, 1930; Heller, 1903; VanDenburgh, 1914, Watson, 1962 This paper Archer, 1948; Leaky, 1944; Watson, 1962 This paper Auffenberg in Campbell and Evans, 1972 VanDenburgh, 1922; Grant, 1936; Nichols, 1953 Campbell and Evans, 1967; Householder, 1950 Hallinan, 1923; Carr, 1952 FitzSimons, 1935 Obstand Meusel, 1965 Mertens, 1946, Watson, 1962; Nikolski, 1915 Chemical signals Not only are chemical signals widespread in reptiles, but they are at least equally as diverse in function as visual, and more diverse than auditory types. When compared to other systems, chemical signals possess several advantages. They can transmit through darkness and around obstacles. Furthermore, they are the only signal type that may be useful in a future context. While chemical signals have a greater potential transmission range than other signal types used by reptiles, in tortoises these signals have a range of from several centimeters to several meters. Scents and musks are commonly produced by turtles (see Mertens, 1946), and tortoises are no exception. While no pronounced musk glands are found on the shell, as in kinosternids and chelydrids, the hinge-back tortoise (Kinixys belliana) exudes a "strong smelling" viscid material from the cloaca when handled (Lang, in Schmidt, 1919). Similar defensive tactics include voiding part of the digestive or excretory contents. Thus Geochelone radiata regurgitates the stomach contents when TORTOISE BEHAVIOR 243 under potential predator attack. Most subdentary gland secretions. He was able species empty the bladder when handled to show that males respond to adults of or otherwise stressed. In addition, the both sexes when the glands of both are large intestine is evacuated by most tor- active, and only to males when the glands toises when under either physiological or are inactive. Females react to males when psychological stress. While none of these the glands of both are active, but do not has.intraspecific communicative functions, discriminate when the glands are inactive. pheromones are used by tortoises for this During the courtship of at least G. purpose. The best known is produced by polyphemus (Auffenberg, 1966; Weaver, the subdentary glands found in the genus 1970) other behavior patterns, such as Gopherus (Fig. 1). head bobbing, are often interrupted by The glands occur in both sexes of all either tortoise wiping the subdentary four extant Gopherus species. During gland over an enlarged scale on the medial breeding they become enlarged, especially edge of one or both forelimbs. The limbs in males. Rose, Drotman, and Weaver are then extended anteriorly, when the (1969) have shown that the protein com- other individual may sniff at them (Fig. 2). position of the gland exudate is sexually Pheromones are also associated with the and specifically differentiated, and that cloaca and perhaps the head. Olfactory esterase composition is species-specific. investigation of the cloacal scent of females That the glands serve as both olfactory and is often a prerequisite to courtship by the visual recognition signals during courtship male (Auffenberg, 19646, 1965, 1966 for and combat has been made reasonably Geochelone travancorica, G. carbonaria and G. clear by Weaver (1970), who has also dem- denticulata, and Gopherus polyphemus respeconstrated that in at least G. berlandieri the tively; Weaver, 1970 for Gopherus berlansecretion is probably partly controlled by dieri). Males also sniff the hindlegs; parboth day length and testosterone level. He ticularly the parts that come into contact concluded that males of G. berlandieri can- with the cloaca, such as the heel. They also not distinguish females entirely by either pay considerable attention to the shell at its cloacal scent, external morphology, or flair over the hindlegs and often seem to movement alone, which suggests that sex- sniff the snout, or perhaps even the air ual discrimination by males may rest exhaled out of the nostrils. MacFarland largely with chemical differences of the (1972) reported that males of G. elephantopus "sniff the air for female scent"; presumably that associated with the cloaca. Scents are also important in a social context. While several pheromones may be involved, the most important seem to be associated with fecal pellet sign posting. Though more evidence is clearly needed, it is suggested in Patterson's work (1971a), as well as in my tortoise compounds at Florida, that fecal pellets of both Gopherus agassizi and G. polyphemus cause dispersal in conspecifics, particularly when the fresh fecals are from a dominant male. Fecal pellets, normally expelled after waking and during the early phases of basking, are commonly distributed near the sleeping pallet (see Auffenberg and Weaver, 1969). The fecal pellet frequently elicits much attention on the part of other individuals, FIG. 1. Adult male Gopherus berlandieri, showing particularly new recruits into the social subdentary glands (arrow) enlarged during the structure. breeding season. 244 WALTER AUFFENBERG facing one another in a head-to-head encounter. The relative unimportance of vision is shown by the fact that seasonal breeding colors are reported only in males of one species (Geochelone travancorica, Auffen- berg, 1964a), and these changes are very slight. Swindells and Brown (1963) reported a similar color change in heatstressed adults of the closely related G. elongata. Positional changes are the most important of the visual signals in tortoises. Ritualized head movements are most common and have been reported in several species. The movements are speciesspecific and apparently based on olfactory motor patterns (Auffenberg, 1965; Weaver, 1970). Much more work is needed on the action patterns of head movements to determine individual and species variation. Ritualized head movements may occur whenever two tortoises meet but are most common and most vigorous in male-male combat and courtship contexts. FIG. 2. External surface of left antebrachium of Gopherus polyphemus, showing enlarged medial scale There is, however, no observable difference in the movements performed in the (arrow) used to rake subdentary glands. different contexts. Courting males usually move their heads more vigorously than females. Movements Visual signals usually occur at a distance of one meter or While it is clear that in lizards visual less. While Weaver (1970) is not certain signals are most important in species iden- that head movements are species-specific tification, as well as the status of individu- in the genus Gopherus, they are clearly so in als within the dominance systems, there is at least one sympatric species pair no evidence that vision is equally impor- (Geochelone carbonaria and G. denticulata, tant in tortoises. However, I have shown Auffenberg, 1965). elsewhere (1965) that visual signals are Tortoise head movements include reimportant in species recognition in at least peated vertical bobbing in some groups some tortoise groups, and that they are (such as Gopherus), or horizontal wagging common components of courtship and in others (subgenus Chelonoides, genus combat. Visual signals are probably not as Geochelone), and sometimes with compoimportant in tortoises because of the posi- nents of both (Geochelone travancorica). tional and visual limitations imposed by Both Weaver (1970) and I (1965) are of the shell and their proportionately short the opinion that these ritualized head limbs. Thus tortoises are probably unable movements are sterotyped, exaggerated to transmit the delicate shading or rapidly movements based on rather simple olfacfluctuating moods of both courtship and tory motor patterns that Eglis (1962) has combat as readily as some other reptiles. shown are characteristic for each major More than in any other reptile, visually- tortoise group. communicating tortoises must be oriented Head position may serve as a visual to one another in such a way that the status indicator among some species. signals can be seen, usually when they are Thus, dominant males of Gopherus berlan- 245 TORTOISE BEHAVIOR dieri and G. polyphemus incline their heads at a higher angle than subordinate males. In courtship the neck of an aroused courting male is fully outstretched and inclined in a high arch. A male thus aroused automatically exhibits a display of dominance and inhibits interruptions by other, less motivated males (Weaver, 1970). MacFarland (1972) stated that combat among when the female stops, the male stops, often moving its head. The significance of the ritual-like cadence of this behavior on the part of both individuals remains unknown. Female Gopherus polyphemus may take a more active role in courtship and approach the male (Auffenberg, 1966). In Homopus areolatus the trailing male progresses along the ground by pushing him adult male Geochelone elephantopus usually self with his rear feet and holding the front ends in victory for the individual whose feet limp (Eglis, 1963). head towers highest. A specific courtship visual display is Tactile signals suggested in only one tortoise species, Communication in tortoises is maximally Homopus areolatus. Eglis (1963) reported that in the courtship of this species the developed in those intimate sequences of male rushes from one side to another of aggregation, combat, and courtship that the female, placing his shell at a 90° angle bring tortoises into bodily contact. While with hers. Whether or not this is an impor- one might presume the presence of the tant communication signal in this genus is shell in tortoises would severely limit the usefulness of bodily contact, this is not the unknown. There is no question but that the sight of case. Tactile signals are reasonably effia moving tortoise is a strong visual signal, cient. particularly during the breeding season. Biting is one of the most obvious of the Several authors (Leakey, 1944; et al.) have tactile signals of tortoises and is used in reported male tortoises following the both combat and courtship contexts (Table female for hours, or even days prior to 2). My earlier comment (1965), that biting breeding. Weaver (1970) calls this trailing may not occur in combat of Geochelone behavior and shows that it marks the be- elephantopus as reported by Van Denburgh ginning of courtship. In Gopherus berlan- (1914), is incorrect in view of MacFarland's dieri the male often follows one to three (1972) descriptions. In combat of all meters behind the female. Most important, species, parts of the adversary may be TABLE 2. Biting reported in the behavior of tortoise species. Species Context Part bitten Chersine angulata Courtship Geochelone denliculala Courtship Geochelone elephantopus Combat Legs Legs Head Courtship Legs Geochelone radiata Gopherus agassizi Courtship Courtship Shell (rare) Edge of shell Gopherus berlandieri Courtship Gopherus polyphemus Combat Courtship Homopus areolala Tesludo hermanni Courtship Courtship Head, legs, and mainly edge of shell Head, legs Head, front limbs and mainly epiplastral projection Head Head, legs Testudo graeca Courtship Head, legs Author(s) Rose, 1950 Beltz, 1954 VanDenburgh, 1914; MacFarland, 1972 DeSola, 1930; MacFarland, 1972; Heller, 1903 This paper Camp, 1916, 1921; Grant, 1946; Woodbury and Hardy, 1948; VanDenburgh, 1922 Weaver, 1970; Householder, 1950 Weaver, 1970 Auffenberg, 1966 Eglis, 1963 Obstand Meusel, 1965; this paper Doumerque, 1899; Nikolski, 1915; this paper 246 WALTER ALFFENBERG bitten, but the head and legs are the usual targets. In the courtship of some species, of some species the ramming is rhythmic and prolonged; in others it is irregular in such as Gopherus berlandieri and Gopherus both cadence and length. It is usually the polyphemus, most of the biting by the male is posterior or lateral slope of the shell that is concentrated on particular parts of the struck. Ditmars (1910) reported a peculiar shell (Table 3). Females never seem to bite. lateral bumping in the courtship of Another important tactile signal is shell Geochelone elephantopus, but he did not deramming during both combat and court- scribe clearly just how it was done. Neither ship. What has not been mentioned previ- MacFarland (1972) nor DeSola (1930) ously is that there are two types of shell mention it. However, something similar ramming. The common form utilizes the occurs in a defensive context in Gopherus epiplastral projection. It may grade into a particularly when the defender is in its pushing or hooking type of behavior. The burrow, plugging the hole with its shell. In other form of ramming utilizes primarily this case the edge of the shell is quickly the thickened anal scute area of the adult thrust laterally against the antagonist. males. To distinguish them, the two types Though it is rare, I have seen a single should be called epiplastral and xiphiplas- lateral head butt used by females of both • tral ramming. Epiplastral ramming is easily Geochelone denticulata and Gopherus and frequently recognized and applies to polyphemus against the heads of aroused, all "ramming" mentioned in the literature courting, conspecific males. so far. Characteristically it occurs when the Epiplastral ramming is also common in male raises himself on four legs, rocks combat among conspecific males, but more backward and then suddenly forward, often it takes the form of pushing, in sending the epiplastral projection crashing which, as soon as contact is made with the into the shell of another individual (Fig. 3). adversary's shell, the hindlimbs are used to The resulting noise can be heard for 100 m push against the ground. Pushing may or so in larger species. Epiplastral ram- occur against any shell surface, but most ming is not accompanied by any other often against the anterior edge of the signal, but it often alternates with head adversary's shell. With the head of both movements and sniffing. During courtship turtles withdrawn, the shells tend to interTABLE 3. Major tactile signals utilizing the shell in tortoises. Species Signal types represented Chersine angulata Geochelone carbonana Geochelone denticulata Geochelone elegans Epiplastral Epiplastral Epiplastral Epiplastral ramming, pushing, and hooking and xiphiplastral ramming, pushing and xiphiplastral ramming ramming and pushing Geochelone pardalis Xiphiplastral ramming Epiplastral ramming, pushing, and hooking Gopherus agassizi Xiphiplastral ramming Pushing and hooking Xiphiplastral ramming, pushing, and hooking Epiplastral and xiphiplastral ramming Pushing Epiplastral ramming, pushing, and hooking Gopherus berlandieri Gopherus flavomarginatus Gopherus polyphemus Testudo hermanni Xiphiplastral ramming Same as G. agassizi Same as G. agassizi Same as G. agassizi Epiplastral ramming and pushing Testudo graeca Same as T. hermanni Geochelone radiata Geochelone travanconca Context Combat Courtship Courtship Combat and courtship Courtship Combat and courtship Courtship Combat Courtship Courtship Combat Combat and courtship Courtship Combat and courtship TORTOISE BEHAVIOR 247 FIG. 3. Agonistic ramming by male Geochelone travancorica during courtship. lock, and the two tortoises push against mon it is usually directed more to the one another until one is forced backward; flange above the hindlegs. Hooking is thus becoming the loser in the contest. often missing in courtship. Most often the pushing in combat has a During xiphiplastral ramming, pushing, definite upward component. The epiplas- or hooking, a common defensive tactic tral projection is placed under the edge of and/or rejection signal is shell drop, in the shell of the adversary and lifted (Fig. which the edge of the carapace is lowered 4). When combined with a forward rush, it to the ground at the point where it is may turn the adversary over. This is usu- touched by the male. The same signal is ally the end of the match. I call such sometimes used by females when mounted behavior hooking. Patterson (1971a) re- by males. Presentation, or shell lift, is a ported that male Gopherus agassizi on their strong tactile acceptance signal in which back may give a call, upon which the victor the posterior part of the shell is lifted, turns it onto its plastron; I have not yet exposing the cloacal area to the caudal observed this particular behavioral se- probing of the male. Another tactile rejecquence, though I have often seen tortoises tion signal is a lateral waggle, in which the rolled over again—sometimes over and female rapidly thrusts her shell from side over several times. When hooking is com- to side—apparently in an effort to dis- FIG. 4. Agonistic hooking behavior by male Geochelone radiata during courtship and combat. 248 WALTER ALFKENBERG lodge or discourage the mounted male. nals. The total compares favorably to that The second major type of shell tactile of total displays in fishes (10-26), birds signal is xiphiplastral ramming. It has not (15-28), or even mammals (16-37). (Data been reported before. Employed only by after Moynihan, 1970) males and restricted to courtship (except While signals used in a sexual context for homosexual activity), it occurs during are obviously important, those related to the times that males are mounted. The agonistic behavior are particularly imporfront feet of the mounted male are used as tant in establishing and maintaining a pivot around which the body swings hierarchies, especially in colonial forms. downward when the rear feet are both The social hierarchy in tortoises is deterlifted off the ground simultaneously in a mined largely by superiority in aggressive short, hop-like movement. At this instant encounters and ultimately regulates order the anal thickening on the xiphiplastron is of access to food or forage areas, mates, slammed against the rear lower part of the and resting sites. In tortoises it is a simple female's shell, making a loud "thud" or system of essentially two levels, the higher "crack" that can be heard for several tens one controlling, at least to some extent, the of meters. At the same time the male may activities of the lower levels, though reverutter a loud "cluck" or similar sound. sals are common. Individuals are conThese are the "thrusting" movements nected by weak social bonds and a few often mentioned in the literature. How- communicative signals. In general, the ever, it is important to point out that at this number of conspecifics contacted by the point intromission has not yet occurred. At average individuals per unit time is low coition these movements are modified so (highest in the more or less colonial that the loud noise and hopping are usu- forms). However, aggression is common in ally absent. Movements are, in general, less adult males during the breeding season, vigorous and cadenced. Tactile signals but may take place during the entire year using the shell are listed and compared in in some species. While non-random spacTable 3. ing is often obvious in colonial species, it is During the xiphiplastral ramming of the not common. In fact, sleeping aggregafemale, the tail of the male of at least some tions are the rule in captive herds of several species may be used to maintain a proper species. mounting position (Auffenberg, 1965; PatDominance is established during initial terson, 19716, 1972). Gopherus agassizi encounters, followed by future individual males use the tail as an aid in attaining recognition in at least captive situations. cloacal contact (Patterson, 19716). This Strength, established through pushing and also occurs during xiphiplastral ramming hooking, is usually the ultimate determinin Geochelone radiata. In this species the tail ing factor, though size and experience are tip is eventually inserted into the cloaca, also important. The losing contender and the tail is then used as a guide by exhibits strong submissive signals (turning which the penis locates, and is finally in- or walking away) that help it to leave the serted into the cloaca. field without being turned over. Other submissive signals are head and limb withdrawal and shell drop. DISCUSSION Courtship of tortoises includes both Compared to lizards, the signal reper- agonistic and sexual signals. In two earlier tory of land tortoises may seem limited. contributions (1964a, 1965) I have tried to However, the minimum total signals emphasize the usual steps of land tortoise utilized in a single species, such as courtship ritual, particularly the early Geochelone radiata, is as high as 15 (plus five phase in which the female is more or less possible ones). Of those that are certain, immobilized. This is usually brought about nine are tactile (plus two?), three are visual by vigorous and repeated biting and/or (plus one?), two are olfactory, and vocaliza- epiplastral ramming by the male. Particution possibly represents two auditory sig- larly aggressive attacks usually result in the TORTOISE BEHAVIOR 249 female withdrawing her head and legs, the probability that the signaler is still in and are often renewed only when the the vicinity. Most important, there is little female again begins to walk away. Im- visual advertisement of sex or reproducmobilization is usually followed by mount- tive status in tortoises. ing and, during the early part of the reStatus signaling is also poorly developed productive period, unsuccessful attempts in tortoises. However, individuals of at at intromission. least some species (usually the larger ones) It is only days or weeks later, after seem capable of discriminating among repeated mating attempts, that the females conspecific individuals. While visual sigseem to become receptive. The seemingly nals are clearly important in many social endless, redundant tactile signals of con- contexts, chemical ones may provide the tinuous epiplastral and xiphiplastral ram- most discriminating signals by which indiming, pushing, hooking, and biting are viduals are separated. Thus, cloacal scent apparently very important in establishing and (in Gopherus) the subdentary glands the pair bond. The repetition may also may serve an important discriminatory serve to awaken a state of arousal in the function. These probably develop in confemale and may serve to alter her repro- junction with the individual's rank, so that ductive physiology as well. Lehrman perhaps only large, dominant males and (1965) and others have shown that male mature females are able to impart their behavior in some birds during early court- own odor signatures. The capability is well ship induces changes in ovarian develop- known in mammals (see Wilson, 1975 for ment and female sexual behavior. Re- review). Reptile pheromones, including peated mounting and copulation in rats those in tortoises, are largely unexplored may increase the amount of sperm trans- and would handsomely repay careful inported to the uterus and also the per- vestigation. centage of successful implantations by fertilized ova (Adler, 1969; Adler, Resko, and REFERENCES Gay, 1970). Crews (1975) has shown that, though climatic factors stimulate ovarian recrudescence in females of the lizard Adler, N. T. 1969. Effects of the male's copulatory on successful pregnancy of the female rat. Anolis carolinensis, male courtship behavior J.behavior Comp. Phys. Psychol. 69(4):613-622. strongly facilitates the environmental ef- Adler, N. T., J. A. Reska, and R. W. Gay. 1970. The fects. 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