AMER. ZOOL., 17:251-260 (1977).

Acoustic and Visual Display Behavior of Gekkonid Lizards

DALE MARCELLINI

National Zoological Park, Smithsonian Institution, Washington, D.C. 20009

SYNOPSIS. Visual and acoustic mechanisms of communication are compared. Their proper- ties are found to be similar except that acoustic systems function more efficiently when light levels are low. The ability of to receive and produce visual and acoustic messages is discussed. Geckos are found to have excellent vision and good hearing. They also possess the visual attributes and sound producing mechanisms necessary for complex displays. The display behavior of geckos is reviewed. Display types are categorized according to the display mechanism used. Visual displays are found to utilize color, pattern, posture, and movement. These displays are used in predator threat as well as in intraspecific social contexts such as aggression and courtship. Combined visual-acoustic displays involve color, pattern, postures, movement, and sound. Combined displays are used in predator threat and in intraspecific aggressive encounters. Acoustic displays have little or no visual component and involve sounds that may be single chirps or temporally patterned multiple chirps. The single chirps are associated with distress while the multiple chirp calls are heard in intraspecific social contexts. The displays of diurnal and nocturnal geckos are compared and it is found that differences are correlated with differences in their diel activity cycles. In conclusion, it is pointed out that many areas remain to be studied before display behavior is well understood.

INTRODUCTION possibilities. In this discussion I will restrict The display behavior of geckos is a fas- myself to the two mechanisms which have cinating field of study for a number of received most of the research attention: reasons: gecko behavior is relatively un- visual and acoustic. known and numerous possibilities for The properties of visual and acoustic study exist; within a single family are two mechanisms of communication are largely very well developed types of display be- similar; both systems provide with havior; geckos are unique among the a rich variety of signals. Optical stimulus lizards in producing complex sounds that variables available are color, intensity or are involved in social behavior. brightness, spatial pattern, postures, and In this paper I will discuss the mech- anisms of communication used by geckos, movement. Acoustic stimuli are at least as diverse including pitch, intensity, fre- summarize their potential for message re- quency, and temporal pattern. Directional- ception and production, review what is ity can be a property of either system and currently known about their display be- havior, and compare gecko visual and with visual stimuli it is inherent in the system. Acoustic stimuli may be directional acoustic display behavior. or not, depending on specific characteris- tics of the signal, and have the additional MECHANISMS OF COMMUNICATION attribute of being able to go around cor- ners. The strength of both systems is good, Geckos have a variety of "choices" for providing reasonable distance communica- channels of communication: chemical, vi- tion, but acoustic signals can be stronger and may be more efficient for long- distance communication. This is particu- I would like to thank personnel of the graphics, management, and education departments of larly true when ambient light levels are the National Zoological Park for their aid in the low. The amount of information conveyed production of this paper. is somewhat dependent upon how quickly

251 252 DALE MARCELLINI one signal follows another. Acoustic sys- with geckos. But some educated guesses tems have a very fast fade rate, while visual can be made on morphology and behavior. systems vary in their fade rates depending The rod retinas of most geckos are proba- upon the stimulus variable being used. bly very sensitive and provide good form Thus, if postures or colors are used, fade is vision. The diurnal geckos, also, no doubt, slow; but if movement is used, fade is fast. have good vision due to areas of concen- A visual display can be physically directed trated cones or other means not yet well at a particular animal and can use stimuli investigated. Behavioral observations appropriate to the receivers' sensory sys- clearly show that both diurnal and noctur- tem. An acoustic display can be very spe- nal geckos have excellent vision. I have cific for a receiving sensory system but observed captive geckos such as the diur- acoustic signals are also frequently nal Phelsuma orienting toward and ap- nonspecific and are heard by animals other proaching crickets at a distance of over than the intended receiver. 3 m. I have also watched the feeding be- In summary, both mechanisms of com- havior of small nocturnal geckos in the munication allow the same types and rich- field. These animals (Hemidactylus frenatus ness of information to be conveyed over Dumeril and Bibron) were seen to orient similar distances. The major difference is toward, and approach a mosquito landing that acoustic systems function more approximately 3 m away. Individuals were efficiently when ambient light levels are also observed watching the flights of small low. insects which were quickly and directly approached when they landed. Many of

MESSAGE RECEPTION these observations were made under low light intensities indicating further that Vision geckos possess excellent visual acuity. Vision is a dominant sense in most liz- Hearing ards, and geckos are no exception. For many years the only general source con- Wever and his co-workers at Princeton cerning the eye was a book by G. L. have investigated hearing in lizards (Peter- Walls (1942) but recently some additional son, 1966; Wever and Hepp-Raymond, work has been done and this is reviewed by 1967; Wever and Werner, 1970). Wever Bellairs (1970) and Underwood (1970). I has shown that a gecko ear is less sensitive will briefly summarize some significant than a typical mammalian ear but that features of gecko visual reception. within a restricted frequency range some The eyes of nocturnal animals are pro- of geckos are as sensitive as many portionally larger than those of diurnal mammals. The range of sensitivity in gec- animals, and nocturnal forms usually kos is from approximately 100 Hz to exhibit larger pupil and lens apertures. nearly 10,000 Hz and greatest sensitivity is Geckos have prominent eyes and noctur- in the 100 Hz-3,000 Hz range. Of the nal members of the superfamily have geckos studied, those with the most sensi- larger eyes than their diurnal relatives tive ears are Coleonyx variegatus Baird and (Werner, 1969). The retinas of most species in the genus Ptyodactylus lizards are composed solely of cone cells that are sensitive to light and color. Most geckos have a retina of light sensitive rods MESSAGE PRODUCTION and probably do not have color vision. The diurnal genera, such as Gonatodes, Phelsu- Visual ma, and Lygodactylus, are known to have a cone retina that is, no doubt, a color recep- The capabilities for producing visual tor. messages are present in geckos. Striking Visual acuity in lizards has not been well patterns of blacks, browns, and whites are investigated and no work has been done common. Vivid colors, from emerald DISPLAY BEHAVIOR OF GEKKONID LIZARDS 253

greens to bright reds, blues, and yellows, kos in the genera Eublepharis, Coleonyx, are found in a number of species. In some, Gonatodes, and Sphaerodactylus frequently colors are combined into patterns giving have hatchlings and young animals which additional display potential. Postures using are more brightly colored or strikingly body, tail, limbs, and head can also be used patterned than are the adults. Coleonyx to produce a message. Movement is variegatus use tail movements and specific another potential source of message pro- postures in response to snake predators, duction. Head jerking, tail waving, strut- and it has been suggested that this be- ting, and even push-ups have been ob- havior results in directing attacks to the tail served. In addition, all of the above visual which is autonomized, allowing the animal capabilities can, and frequently are, com- to escape (Johnson and Brodie, 1974). I bined to produce a message. have observed Eublepharis (particularly juveniles) to respond to a human threat by vigorous tail waving and postures (Fig. 1). Acoustic Many threat displays do not involve Geckos have long been renowned among color or striking patterns but do have the lizards for their abilities to produce strong postures and vigorous movements sounds (Smith, 1849; Evans, 1936; associated with them. Defensive displays in Mertens, 1946). Acoustic signals can be response to humans have been reported in produced by the integument, such as in the genera Diplodactylus, Phyllurus, Gehyra, the genus Teratoscincus which makes a Heteronotia, Hemidactylus, Teratoscincus, noise by rubbing caudal scales against one Nephrurus, Gekko, and others (Bustard, another. Geckos are apparently unique 1965, 1967; Mebs, 1966, 1973). These dis- among the lizards in possessing vocal cords plays frequently make use of limb exten- (Gans and Maderson, 1973) and this al- sion, back arching, inflation of the lungs, lows them to produce complicated vocali- and tail waving. Some of these displays also zations. Sounds range from barely audible involve limb extension and retraction, squeaks and chirps to loud growling and either a single motion (Phyllurus) or a con- barking noises. Many geckos have local tinuous series of motions for several min- names onomatopoeically derived from the utes (Nephurus). The above threat displays sounds they make: Hemidactylus frenatus is can be performed by males and females called "chee chak"; Gekko gecko Lauranti is but are more common in males. "tokay." Threat displays are known to be used during intraspecific encounters as well as in a response to predators. I have observed DISPLAY BEHAVIOR Gekko gecko and Teratoscincus scincus Schle- Visual displays gel use similar visual threat displays to conspecifics as they use in response to For this discussion I have placed visual human threats. It is not known if the other display in two contextual categories: threat genera mentioned above use predator or defensive—a display performed during threat displays during intraspecific en- a threat by a predator or during aggressive counters but indirect evidence that they do interactions with other geckos; court- can be derived from the discussion that ship—a display performed to members of follows. the opposite sex prior to copulation. Many geckos perform visual threat dis- Defensive or threat displays are com- plays that are directed at conspecifics, but mon in adult and juvenile geckos of both these have not been reported to be used in sexes. These are largely performed by defense against a predator. Visual displays nocturnal geckos and require proximity to during aggressive encounters have been stimulate the display. The simplest of these reported in the genera Coleonyx, Lucasius, involve striking colors or patterns which Hemidactylus, Lygodactylus, and Phelsuma when coupled with movement may func- (Bustard, 1965; Greenberg, 1943; Greer, tion to startle or confuse a predator. Gec- 1967; Marcellini, 1974), and I have ob- A###WWk 4WM*W##

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FIG. 1. Sonagrams of threat calls and drawings of threat postures for three species of gecko. served visual threat displays in Ptychozoon The display of the nocturnal gecko and Gonatodes. These displays use posture, Ptychozoon lionatus Boulenger differs from movement, color, and pattern. the above pattern in that the body is held The nocturnal genera Coleonyx, Lucasius, low and the hind quarters are alternately and Hemidactylus have very similar dis- raised and lowered. This is accompanied plays. These displays have only been re- by the moving of the tail over the back at ported to occur between males who are in nearly right angles with the longitudinal close proximity. The body is arched and axis of the body. held high by the extended limbs while the The diurnal genera Gonatodes, Lygodac- head is usually held low. The geckos orient tylus, and Phelsuma have intraspecific threat with their flanks parallel to each other and displays that involve pattern, color, and after some circling may attempt to bite movement to a greater degree than noc- their rival (Fig. 1). turnal genera (Greer, 1967; Kastle, 1964). DISPLAY BEHAVIOR OF GEKKONID LIZARDS 255

In a typical display the body is raised, the what might be called display. The male back is arched, the nose is pointed slightly approaches the female with head and body down and the throat may be distended. low and with tail waving. He may lick her The displays are given in a head-on or briefly or merely pounce and bite finally broadside position and the body positions securing a neck hold. I have similar obser- may be changed as an animal moves closer vations on Hemidactylus frenatus and H. to an antagonist. These postures are ac- turcicus Laurenti. companied by side-to-side movements of The visual courtship displays of diurnal the head. geckos are in marked contrast to those of In many diurnal geckos, colors are vivid nocturnal species. Displays are elaborate and color differences between the sexes and involve postures, movement, pattern, may exist. Postural attitudes are used by and color. Courtship displays have been these geckos to better display colors and described for the genera Phelsuma and patterns. Phelsuma tilt their bodies toward Lygodactylus (Kastle, 1964; Greer, 1967), an opponent showing their bright red or and I have observed courtship in Gonatodes. blue dorsal markings. Lygodactylus distends The courtship displays appear nearly iden- its throat exposing a black patch and in- tical to the threat displays for these genera. flates its abdomen showing a yellow mid- The males begin to posture at a distance ventral stripe. from the female of a few centimeters to up The visual threat displays described for to 100 cm. Displays consist of raising the diurnal species of geckos differ from those body, arching the back, distending the of nocturnal species in that they can ap- throat and posturing to expose color and parently be performed by both males and patterns. Lateral head movements are also females (more commonly by males) and a part of the courtship display. If the fe- they do not require close proximity to elicit male does not move off, the male will grasp a display. the skin of her nape in his mouth and The similarity between threat displays copulate. Females are largely passive but directed at predators and those directed at sometimes will actively solicit the male by con specifics suggests that many of the gen- approaching, nipping, and tail waving. era above may be found to use their in- Visual courtship displays in geckos may traspecific displays in response to predator function in the same manner as visual threat. displays of other lizards. It has been The function of visual threat displays suggested that male displays attract directed at conspecifics is not known. The females and allow females to recognize close range threats in nocturnal geckos males of their own species (Carpenter, may act to intimidate a rival prior to actual 1967; Hunsaker, 1962). fighting. When given at a distance the threat displays of diurnal geckos may func- tion in territoriality or spacing as has been suggested for visual displays of non- Visual-acoustic displays gekkonid lizards (Carpenter, 1967). Visual displays may have acoustic ac- companiments; they are also frequently produced alone. However, there are no Courtship displays reports of the acoustic portion alone; it is always heard coupled with a visual display. Courtship in geckos has only been de- Combined displays have only been ob- scribed in a few species, but it appears that served in threat contexts either in response differences, exist between diurnal and noc- to a predator, or in aggressive interactions turnal animals. Greenberg (1943) de- with another gecko. Males and females will scribed courtship copulation encounters in produce threat sounds when approached the nocturnal species Coleonyx variegatus. by a predator but apparently only males This animal demonstrates very little of vocalize during intraspecific aggressive en- 256 DALE MARCELLINI

counters. Threat sounds in response to a Acoustic displays human predator have been reported in the following genera: Gekko, Diplodactylus, These displays are produced with little Lucasius, Nephrurus, Phyllurus, and Terato- or no visual accompaniment. Two types of scincus (Bustard, 1965, 1967; Mebs, 1966; gecko vocalizations fall into this category: Wever et al., 1963). In addition I have the single chirp or distress call and the heard Eublepharis macularis Gray produce a multiple chirp call (Marcellini, 1974). threat call in response to a human. These Single Chirp (SC): these vocalizations sounds, all associated with visual displays, are the most commonly heard sounds pro- are produced at very close proximity to the duced by geckos. They have been reported predator; and are thought to startle it for many genera and occur in both noc- allowing the gecko time to escape. A typi- turnal and diurnal geckos (Frankenberg, cal threat sequence is described for Nep- 1975; Greenberg, 1943; Kastle, 1964). hrurus asper Gunther (Bustard, 1967). This Single chirps are frequently produced by gecko postures, does push-ups, and when geckos when they are captured or hand- prodded lunges at its tormentor and utters led. They also occur during interaction rasping noise. between individuals. Both sexes produce Threat sounds produced during intra- this call although males do so more fre- specific interactions have been reported in quently. In intraspecific interactions the the genera Phelsuma, Lygodactylus, and call is produced when one animal bites or Hemidactylus (Kastle, 1964; Marcellini, nudges another. In Coleonyx, Greenberg 1974). I have also observed Gekko gecko to (1943) describes single chirps being pro- use a threat call during intraspecific in- duced when a male bites another male teractions. These calls are associated with during aggressive encounters. I have re- the previously described visual displays ported a similar context for this call in and are produced when animals are in Hemidactylus frenatus (Marcellini, 1974). I close proximity. They may function as a have also observed H. turcicus females to last minute intimidation or to startle an use this call while being bumped and antagonist. A typical intraspecific threat is licked by males. described for H. frenatus (Marcellini, Sonagrams of single chirp calls of 1974). Males posture vigorously from close Hemidactylus frenatus and H. turcicus are to their opponents until one of the animals shown in Figure 2. The H. frenatus call was lunges at the other, opens his mouth and produced during handling of a male while utters a rasping call. the H. turcicus call was given by a female Sonagrams of threat calls and associated when bumped by a male. The H. turcicus postures for three species of geckos are single chirp is accompanied by a male shown in Figure 1. The calls for Gekko and multiple chirp call. These and other pub- Eublepharis are in response to a human lished sonagrams of single chirp calls indi- predator while that of Hemidactylus was cate that the sounds are short and begin recorded during an intraspecific aggres- and end abruptly (Frankenberg, 1975; sive,encounter. The vocalizations are all Marcellini, 1974). The calls cover a wide relatively short-duration single bursts of frequency range with dominant frequenc- sound with a dominant frequency that ies from 1000 Hz to 5000 Hz and har- varies from 1,000 Hz in Eublepharis to monics to over 8000 Hz. Loudness varies: 4,000 Hz in Gekko gecko. All three sounds Some chirps can be heard only at distances have harmonics that cover a reasonably under a few meters, while others are audi- wide frequency range. Intensity varies; the ble over 10 m away. Eublepharis call is audible from only a few There are a number of speculations meters while Gekko is easily heard from about the functions of the SC call. It might over 20 m. The threat sounds of other facilitate escape from a predator. The geckos appear to have properties similar to chirp expels air from the lungs making the these, although little quantitative data is lizard smaller; the sound might also startle available. the attacker. It has also been suggested DISPLAY BEHAVIOR OF GEKKONID LIZARDS 257

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that the sound functions as a release call diurnal retreats. Frankenberg (1974) men- during intraspecific interactions. Franken- tions that geckos may call in response to berg (1975) reported that a male Ptyodac- another animal's call. Curry-Lindahl tylus released a hold on a female when she (1961) states that Hemidactylus mabouia produced an SC call. But I have observed Moreau de Johnes call upon seeing their both male and female Hemidactylus to ig- mates. Hemidactylus frenatus uses multiple nore single chirps produced by animals chirp calls in a variety of social situations they held. (Marcellini, 1974). Males often produce Multiple Chirp (MC): The multiple the MC call when sighting an alien male at chirp call is a common vocalization that has a distance. Aggressive encounters some- been reported in a large number of genera times start with an exchange of calls and (Brain, 1962; Evans, 1936; Loveridge, conclude with an MC call by the victor. In 1947; Mertens, 1955; Schmidt and Enger, courtship copulation encounters males 1957), but not in diurnal geckos. It can be often utter the call prior to approaching produced by both males and females but is the female. much more common in males. Multiple Sonagrams of male MC calls of four chirps are given in a variety of contexts but species of geckos are shown in Figure 3. are more commonly heard during social These plus published sonagrams for the interactions. Haacke (1969) states that calls genera Ptyodactylus (Frankenberg, 1974) are produced when animals emerge from and Ptenopus (Haacke, 1969) allow some 258 DALE MARCELLINI

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generalizations concerning call structure. ported change in call structure with con- The MC call consists of a series of chirps or text: male-male calls differ from male- barks that are produced in a temporal female calls in being more protracted. Var- pattern. The dominant frequency varies iation in MC calls between species has been from 500 Hz to 6000 Hz with harmonics to mentioned by Haacke (1969) and Werner over 10,000 Hz. (1965). Species differences in duration of Calls produced by an individual may pauses and chirps, intensity pattern of vary in number of chirps but are uniform chirps, and physical characteristics of the in structure. Frankenberg (1974) has re- chirps are apparent in Figure 3. But, it DISPLAY BEHAVIOR OF GEKKONID LIZARDS 259 would be premature to postulate taxon- The lack of a courtship display in noc- specific calls on the basis of the limited turnal geckos may be due to differences in information which now exists. ambient light levels. In diurnal geckos the The variety of contexts reported for the female can see the males and thus must be MC call make functional interpretations displayed at in order to keep her from difficult. Functional suggestions range escaping. In nocturnal geckos the male can from the attraction of insects (Beebe, approach closely without being clearly 1944) to the more plausible possibility that seen, rush the female and mate with her. the calls are important in social behavior The multiple chirp call produced by (Wever et al., 1963). They may play a part nocturnal geckos appears to replace a part in territorial behavior (Mertens, 1946; of the visual conspecific threat display of Werner, 1965) and might act to attract diurnal geckos. A visual threat at a dis- females (Mertens, 1946). The fact that MC tance would not normally be possible in calls can also be produced by females nocturnal geckos because of low light in- makes the territorial!ty hypothesis more tensities. An acoustic display would serve compelling. to declare an individual's presence from a I developed an experimental procedure distance thereby reducing territorial dis- to test the functional significance of the putes and fighting. MC call of Hemidactylusfrenatus (Marcellini, 1977). A male call was played to females and males in a choice situation. Females CONCLUSION made no directed response to the call but males gave a significant negative response. The display behavior of gekkonid Thus, it appears that a function of the MC lizards has only relatively recently come call may be in spacing or territoriality. under investigation and the study of their acoustic behavior is in its infancy. This review paper serves to point out many COMPARISON OF THE DISPLAYS OF NOCTURNAL areas where work is badly needed. Addi- AND DIURNAL GECKOS tional species need to be studied particu- larly in the more primitive subfamilies. Table 1 shows a comparison of the dis- Quantitative descriptions of the displays play types of nocturnal and diurnal gec- are needed. This is especially true if we kos. The similarities in the display be- expect to determine if the displays are havior should not be surprising. The two taxon-specific. The functions of many of groups have had a common ancestry; they the displays need to be clarified. This can have similarities in their population ecol- be accomplished by additional contextual ogy and social systems. As a result they data but experiments must also be per- have the same messages to transmit. The formed. The challenges are clear: We few differences in display behavior are no need only to apply ourselves. doubt due to the differences in their activ- ity cycles. TABLE 1. Comparison of display types found in nocturnal Visual and acoustic predator threats are and diurnal geckos. not found in diurnal geckos. It would seem adaptive for a diurnal lizard to rely on Display type Diurnal Nocturnal spotting a predator at a distance and then Visual rapidly seeking shelter rather than allow- predator threat no yes ing a predator to approach closely before conspecific threat yes yes utilizing a threat display to stop the pred- courtship yes no Visual and acoustic ator momentarily. A nocturnal gecko, predator threat no yes however, has a greater chance of being conspecific threat yes yes surprised and thus needs to rely on a Acoustic strong threat to stop a predator allowing single chirp—distress call yes yes the gecko to escape into the darkness. multiple chirp call no yes 260 DALE MARCELLINI

REFERENCES Kastle, W. 1964. Verhaltensstudien an Taggeckonen der Gattungen Lygodactylus und Phelsuma. Zeitschr. Beebe, W. 1944. Field notes on the lizards of Kartabo, Tierpsychol. 21:486-507. British Guiana, Caripito, Venezuela. Part I. Gek- Loveridge, A. 1947. Revision of the African lizards of konidae. Zoologica 29:145-160. the family Gekkonidae. Bull. Mus. Comp. Zool. Bellairs, A. 1970. The life of , Vol. II, pp. 98:1-469. 342-350. Universe Books, New York. Marcellini, D. L. 1974. Acoustic behavior of the Brain, C. K. 1962. A review of the gecko genus gekkonid lizard, Hemidactylus frenatus. Her- Ptenopus with the description of a new species. petologica 30:44-52. Cimbebasia 1:1-18. Marcellini, 0. L. 1977. The function of a vocal display Bustard, H. R. 1965. Observations on Australian of the lizard Hemidactylus frenatus. Anim. Behav. (In geckos. Herpetologica 4:294-302. press) Bustard, H. R. 1967. Defensive display behavior of Mebs, 0. 1966. Studien zum aposematischen Verhal- the Australian gecko Nephrurus asper. Her- ten von Teratoscincus scincus. Salamandra 2:16-20. petologica 23:126-129. Mebs, D. 1973. Drohreaktionen beim Blatt- Carpenter, C. C. 1967. Aggression and social struc- schwanzgecko, Phyllurus platurus. Salamandra ture in iguanid lizards. In W. W. Milstead (ed.), 9:71-74. Lizard ecology: A symposium, pp. 87-105. Univ. Mis- Mertens, R. 1946. Die Warn-und Droh-Reaktionen souri Press, Columbia. der Reptilien. Abh. Senckenberg. Naturforsch. Curry-Lindahl, K. 1961. Contribution A 1'etude des Ges. 471:1-108. vertebres Terrestres en Afrique Tropicale. Explo- Mertens, R. 1955. Die Amphibien und Reptilien ration du Pare National Albert et du Pare National Sudwestafrikas. Natur. Ges. 490. de la Kagera-ii. Mission K. Curry-Lindahl (1951- Peterson, E. A. 1966. Hearing in the lizard: Some 1952, 1958-1959). 1, P. 41. comments on the auditory capacities of a non- Evans, L. T. 1936. The development of the cochlea in mammalian ear. Herpetologica 22:161-171. the gecko, with special reference to the cochlea- Schmidt, K. P. and R. F. Inger. 1957. Living reptiles of lagean ratio and its bearing on vocality and social the world. Doubleday Co., Garden City, New York. behavior. Anat. Rec. 64:187-201. Smith, A. 1849. Interior of South Africa. Illus. Zool. Frankenberg, E. 1974. Vocalization of males of three S. Africa, Rept., Appl, p. 6. geographical forms of Ptyodactylus from Israel (Re- Underwood, G. 1970. The eye. In C. Gans and T. S. ptilia: Sauria: Gekkoninae). J. Herp. 8:59-70. Parsons (eds.), Biology of Reptilia, Vol. 2, pp. 1-97. Frankenberg, E. 1975. Distress calls of gekkonid Academic Press, New York. lizards from Israel and Sinai. Israel J. Zool. 24:43- Walls, G. L. 1942. The vertebrate eye and its adaptive 53. radiation. Bull. Cranbrook Inst. Sci. 19:1-785. Gans, C. and P. F. A. Maderson. 1973. Sound produc- Werner, Y. L. 1965. Uber die Israelischen Geckos der ing mechanisms in recent reptiles: Review and Gattung Ptyodactylus und ihre Biologic Salamandra comment. Amer. Zool. 13:1195-1203. 1:15-25. Greenberg, B. 1943. Social behavior of the western Werner, Y. L. 1969. Eye size in geckos of various banded gecko, Coleonyx variegatus Baird. Physiol. ecological types (Reptilia: Gekkonidae and Zool. 16:110-122. Sphaerodactylidae). Israel J. Zool., 18:291-316. Greer, A. E. 1967. The ecology and heavior of two Wever, E. G., D. E. Crowley, and E. A. Peterson. sympatric Lygodactylus geckos. Breviora 268:1-17. 1963. Auditory responses in the tokay gecko. Proc. Haacke, W. D. 1969. The call of the barking geckos Nat. Acad. Sci. 50:806-811. (Gekkonidae: Reptilia). Sci. Pap. Namib Desert Res. Wever, E. G. and M.-C. Hepp-Reymond. 1967. Au- Sta. 46:1-469. ditory sensitivity in the fan-toed gecko, Ptyodactylus Hunsaker, D. 1962. Ethological isolating mechanisms hasselquistii puiseuxi Boutan. Proc. Nat. Acad. Sci. in the Sceloporus torquatus group of lizards. Evolu- 57:681-687. tion 16:62-74. Wever, E. G. and Y. L. Werner. 1970. The function Johnson, J. A. and E. 0. Brodie Jr. 1974. Defensive of the middle ear in lizards: Crotaphytus collaris behavior of the western banded gecko Coleonyx (Iguanidae). J. Exp. Zool. 175:327-342. variegatus. Anim. Behav., 22:684-687.