Comprehensive Description
provided by Smithsonian Contributions to Zoology
Microgale dobsoni
Physical Description
Microgale dobsoni is a large, terrestrial Oryzorictine with a head-and-body length ranging from 92 to 114 mm and a tail length from 102 to 108 mm. Its hind foot averages about 21 percent of the head-and-body length. The dorsum is gray-brown in color contrasting with the gray ventrum. The tail is faintly bicolor (see Figure 22). The weight of the animal varies with the season. For example, adult weights, without fat reservoirs, range from 34 to 45 grams; however, with the onset of the austral winter, they accumulate fat reserves in the tail and body and weights may reach 84.7 grams in captivity. Captive specimens retain a tendency for seasonal fluctuations in weight, reaching a maximum in November and December and declining until May when an increase occurs again.
Sexes are not readily distinguished by conspicuous morphological features. Since the animals possess a cloaca, they must be sexed by expressing the phallus by means of slight pressure on either side of the anterior edges of the cloacal lips. Out of a sample of eight living specimens collected for captive studies, five were males and three were females.
Distribution and Habitat
This species has been taken over a broad range from northern Betsileo to Lake Aloatra. Two trapping localities yielded Microgale dobsoni during the current study. One included three stations at 4.6, 5, and 11.5 kilometers east of Manandroy; the other was near Manohilahy approximately 20 kilometers west of Lake Aloatra. The trapping site at 11.5 kilometers east of Manandroy is especially instructive since this locality is still to the west of the divide which separates the climatically distinct high plateau edge from the eastern escarpment rainforest. For example, 11.3 kilometers further to the east, one is already in a region of multistratal tropical evergreen forest where Microgale talazaci may be trapped. At the trapping locality for Microgale dobsoni, the habitat is characterized by a seasonal rainfall and probable seasonal abundance in insects. One area at 11.5 kilometers east of Manandroy is shown in Figure 23 and exemplifies a typical second-growth area probably once occupied by transitional forest between the high plateau forest and the eastern rainforest but now reduced to scrub.
The trapping area was selected to include an interface between a marsh and second-growth brush. A line of 100 traps was laid in such a way as to include high, dry ground and by gradually descending down a slight slope toward a stream running through the marshy area, the line eventually intersected with a second wooded tract. Eight Microgale dobsoni were taken and of the eight only one occurred in the high dry area, the rest being taken at the interface between marshy bog and the second-growth scrub. A total of nine M. dobsoni were taken in 125 trap nights6 at the 11.5 kilometer area. Three others were taken in 45 trap nights in the areas 4.6 and 5 kilometers east of Manandroy.
Microgale dobsoni was abundant in the forested regions of Manohilahy (Figure 24). Seventeen specimens were trapped in 136 trap nights on 18 and 19 April. M. dobsoni was taken where the soil and leaf litter of steep forested slopes was moist and friable, similar to the floor of the rainforest. There were no orchids, however, and there were virtually no insect sounds in contrast to the cacophony of the rainforest region of Perinet in April. Tenrec ecaudatus were torpid but Microcebus were seen active in the dense shrubbery along the road. The tails of M. dobsoni were not yet fat.
The Annual Cycle, Reproduction, and Thermoregulation
We have little data on reproduction and growth for this species. Copulation in captivity will take place during the months of December through August and captive births have occurred in February and May. However, during the trapping in the month of April near Manandroy, no lactating animals were taken and, of the eight specimens which were taken alive, none could be considered fully adult.
In captivity, special attention was directed toward weight changes and thermoregulation (see Appendix C for an outline of thermorecording techniques). As noted before, Microgale dobsoni has the capacity to store considerable quantities of fat. In captivity marked fat storage will occur throughout the year if the animals are fed to excess and weight can be controlled only by limiting the diet. There is some seasonal tendency for the weights to rise and fall in captive individuals but this was masked to some extent by the relatively constant conditions under which we attempted to maintain them. Microgale dobsoni at no time showed any tendency to enter profound torpor, but when it becomes heavy in captivity, it will show a tendency to decline in body temperature and become inactive, eating less, and sleeping a great deal. During these periods of inactivity, there is a slight tendency for cloacal temperatures to parallel the ambient temperature when the latter is between 21° and 28.5° C. Over this range, the cloacal temperature varied between 24.5° and 32° C. Hence, it would appear that when Microgale dobsoni has sufficient fat reserves it will allow its body temperature to oscillate slightly within a denned range according to the fluctuation in the ambient temperature.
This fat storage phenomenon and slightly unstable body temperature probably reflect an overall adaptation to life on the high plateau edge. Although occurring in the reasonably moist area, these animals must at certain times of the year experience shortages in moisture and insects. At this time, they undoubtedly live on their fat reserves and further conserve energy by reducing metabolic rate. Our inability, however, to duplicate exactly the environmental fluctuations in the laboratory prohibited testing the hypothesis that the fat reserves may change with seasonal changes in ambient conditions.
Feeding Habits
Microgale dobsoni was tested in captivity with a variety of foodstuffs and we found that it would quite readily take orthopterans, coleopteran larvae, earthworms sparingly, and raw ground meat. By observing their method of hunting orthopterans, it was quite evident that such insects provide staples in their diet. It also seems useful to repeat comments from the residents of Manandroy. One individual stated that M. dobsoni may supplement its diet with ant eggs. Indeed, one specimen was trapped within 2 1/2 feet of an ant nest. Further discussion of prey-catching behavior will follow in the next section.
Ethological Studies
GENERAL MAINTENANCE BEHAVIOR
Locomotion.—Microgale moves about in a stereotyped fashion. On a plane surface the basic pattern is the crossed extension mode of locomotion where the contralateral limbs are in synchrony. The tail is generally held somewhat off the substrate but its exact position depends on the degree of muscular tension in the animal's body. The tail may be quite stiffly extended as the animal explores a new area, but as it becomes more relaxed the tail may drag. The animal is able to leap a short distance if in pursuit of an insect or when climbing. In climbing a similar crossed extension pattern of limb coordination can be observed. The tail may aid the animal to maintain its balance while climbing. Most of the activity of M. dobsoni takes place at night.
Exploration and utilization of the living space.— Laboratory observations in an open field testing situation indicate that Microgale dobsoni climbs readily and well. A variety of tree limbs may be climbed and the animal may spring a short distance (1 inch) from one branch to another. During exploration the animal pauses frequently to sniff the substrate. The nose is somewhat mobile but the vibrissae are rather stiff. The animal will poke its nose under leaves or into the substrate, pausing to sniff in any place where prey may be hiding.
When placed in a novel environment, the animal frequently shows some period of hesitancy and exhibits a stiff or tense body posture, pausing from time to time to test the air and may even assume an upright posture while sniffing. It will then begin to progress more rapidly about the cage utilizing some of the same spots over and over again for urination and marking.
Rest and sleep.—Typically the animal adopts a curled posture when sleeping, with the head tucked ventrad. The animal may lie curled on its side or may rest its weight on the hind feet and the dorsal surface of its head.
Marking.—Chemical communication by marking with exudates from the cloacal region is very characteristic of M. dobsoni. Marking behavior is exhibited by both males and females during an encounter and when exploring a new area. The animal typically selects a spot near a nest box or an artifact such as twig or log and marks by depressing its perineal region upon the substrate and, while moving forward, drags the cloaca repeatedy on the same spot.
In addition we have noted that the males frequently secrete a white fluid around the eye. This secretion is sometimes apparent when the male is excited after having been placed with a female. It does not always occur during an encounter and no specific marking movement has been noted in conjunction with the secretion (see Setifer, pages 54 and Echinops, pages 62).
Care of the body surface.—Three basic patterns of auto-grooming may be noted. These include scratching, licking, and washing. Washing involves sitting upright, bearing the weight on the hind legs and the base of the tail, while depressing the head forward. By bringing up the forepaws simultaneously on either side of the face, it will down-stroke with its forepaws on the sides of the face beginning behind the ears and brushing the fur all the way to the tip of the nose. As the paws pass the mouth, the mouth is opened slightly and the paws appear to be somewhat moistened with saliva during this terminal part of the stroke. This action may be repeated several times (see Figures 25 and 26). Such an activity probably serves a dual function. The motion of the forepaws would aid in cleaning dirt and particles away from the eyes and the nostrils and also would tend to clean the vibrissae. At the same time, impregnation of the forepaws with saliva would serve, on subsequent movements, to spread saliva over the head and face of the animal. This may be vital in chemical communication during an encounter between two individuals.
Scratching is the second major cleaning movement, being directed at the head, ears, shoulders, and ventrum—wherever the hind foot can reach.
The cloacal region may be licked and following copulation the male has been noted to lick his penis. The tongue and teeth are also employed in licking the ventrum and nibbling the toenails after an extended scratching bout.
Nest building and burrowing.—Detailed observations on burrowing behavior have not been carried out with M. dobsoni. The typical digging pattern involves alternate movements with the forepaws and kicking back the earth accumulated under its body with the hind feet If a suitable nest box is provided, the animal will initiate nest building behavior. This consists of moving about in its living space and selecting pieces of dried vegetation such as leaves and grass stems and then carrying them back to the nest box in its mouth. Nesting material is collected in the nest box and the turning movements of the animal's body suffice to form a cup.
Prey-catching behavior and feeding.—When foraging the animal moves about sniffing the substrate, pausing to dig from time to time or insert its nose under leaves or fallen branches. If it hears an insect moving, such as a grasshopper, it will assume an elongate posture and rush suddenly at it attempting to seize it with its mouth. It may half spring toward an insect and pin it down with the forepaws while simultaneously biting it. The forepaws are not used to hold the food. The animal may pin down the food with the forepaws and chew, shaking its head occasionally from side to side to tear off pieces but chewing and shaking may proceed without using the forepaws. Insect prey may be carried into or near the nest box where it is devoured. No highly developed tendency to cache food has been displayed by M. dobsoni. Chewing movements involve an up and down motion of the jaw with no lateral movement discernible.
Defensive and offensive behavior.—When tested with the odor of Galidia elegans, M. dobsoni will turn immediately and exhibit the defense reaction. During this behavior, the month is held widely open and the animal remains orientated toward the odor source. Typically the animal is silent and shows only the gaping response but it may emit a squeal or a prolonged squeal, termed a scream. If a finger or foreign object is poked at the animal during the gape response and the vibrissae are touched, it will bite vigorously. If the animal is moving about in a novel living space and suddenly startled, it will attempt to escape by fleeing to the nearest cover.
SOCIAL BEHAVIOR
Communication.—In this and all subsequent sections dealing with social behavior, a social context includes that situation which involves two or more interacting conspecifics. By interacting the animals are exchanging some form of information and this leads to a second definition. When a discrete behavior pattern of one animal causes a response on the part of a second animal, we may speak of a communication system with the first animal acting as the sender and the second acting as the receiver (Eisenberg, 1967; Marler, 1961). We may consider the mode of communication in terms of the sense organs involved, such as visual, tactile, auditory, or chemical signals. Since the eyes of the Microgale are so reduced in size, we may rule out any discrete forms of visual communication; indeed, it would appear that almost all information exchange between or among Microgales involves audition, chemical cues, or tactile input. When interacting, the animals may influence one another by the sounds of their movements, such as rustling through the leaf substrate. When slightly alarmed the Microgale may exhibit a general trembling and pattering with a forepaw but this appears to be unritualized.
Vocal communication involves the following categories: a soft squeak which may be repeated and termed a twitter; a louder squeal which may, under higher intensities of motivation, be emitted as a long squeaking trill; and finally, a prolonged emission which may be termed a scream or wail. These three types form a graded series. In addition, there is a sound type with low frequency components which may be termed a churr or buzz (see Table 4 and Figures 27 and 28).
Tactile communication occurs during contact configurations such as nose to nose contact, nose to ear, nose to side, nose to anal genital region, and during all forms of rubbing the sides together or crawling over and under one another.
Chemical communication has been indicated under marking and we have also inferred that chemical communication may be involved when saliva is spread on the face during washing behavior. In addition, it should be noted that under the heading tactile communication, we have discussed several postures which involved touching the nose to glandular areas such as nose to ear, nose to crown, nose to nose, and nose to cloacal area. These sites for tactile input involve corresponding glandular areas and all such areas are potential sources for chemical cues. Contact configurations must not be underrated in any extended discussion of Microgale behavior; however, we are lacking the experimental evidence to confirm the exact role of such configurations in the integration of behavior.
The white secretions from the glands associated with the eye of the male may also serve in chemical communication but the functional significance is obscure.
The encounter.—The behavior of Microgale dobsoni, upon introducing a conspecific, permits us to describe a number of interactions based on a functional classification. Several types of encounters were run following a methodology described by Eisenberg (1963). (Refer to Appendix D for a discussion of encounter techniques.)
All things being equal, the following generalizations can be made concerning the behavior of encountering animals. If a stranger is introduced into a resident animal's cage, the resident will generally show defensive behavior or attack toward the alien during the initial phases of the encounter. An encounter on neutral ground generally involves only cursory contact which may later be followed by overt sexual behavior in the case of a male-female encounter or in a male-male encounter by attempts toward sexual contact by a dominant male with agonistic behavior on the part of the subordinate. This latter behavior on the part of the subordinate may lead to a fight. Perhaps the simplest way to describe the behavior of M. dobsoni in a social context is to cite four actual protocols.
The first type of interaction typifies an encounter between three strangers in a neutral area, that is, an area in which none of the animals has had experience.
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Two animals actively exploring in the arena: First animal is investigating the underside of a leaf lying on the soil. Second animal approaches, contacts its tail and turns away to initiate independent exploring. Second animal approaches first animal again and contacts it nose to side. Animals stand with body axes parallel, both nuzzling each other in the inguinal region. Second animal breaks and moves away; first animal follows nose to rump, nose to base of tail, then breaks off while second animal moves away. Contact again between a third individual and the first animal; mutual nose to inguinal region; body axes parallel but oriented in opposite directions. Third animal puts head under first animal's body; first animal starts to move away; then first animal exhibits nose to nape of neck while third animal places its nose in the cloacal region of the first; crawling over by the first animal and grooming the third animal who is crawling under. Forepaws of first animal on rump of third animal as third animal moves away; break off. First animal encounters third animal, nose to side, nose to nape; third animal gapes, opening mouth widely. First animal moves away and proceeds exploring alone.
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Second example of encounter behavior. Male introduced to second male's cage: Alien male approaches resident who approaches also. Alien male utters a soft squeak; resident utters a buzz. Body axes aligned parallel with mutual nose to perineal region of partner. Alien continues to press nose into perineal region of resident male; resident male rolls onto his back. Break apart. Contact between alien male and resident, mutual gaping. Alien male squeals which grades into a prolonged trill. Open mouths are interlocked. Break off and move away.
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Example of male-female encounter with the female partially receptive: Animals contact and pass with body axes parallel to one another rubbing their sides; reencounter nose to nose, then nose to side by male, followed by nose to perineal region of female. Male begins squeaking and trilling—break apart. Repeat procedure and then male stands while female touches nose to side of male, then she places her forepaws on the male and male rolls over onto his back. Female nibbles and bites at his hair, actually pulling some strands of hair out. (This is grooming behavior but with aggressive overtones.) After a continuation of the contact promoting behaviors with grooming the male mounts and thrusts approximately 19 times in about 10 seconds. He then dismounts and licks his phallus. During the mount and thrusts, the female gaped and squealed, pulling away, thus terminating the mount sequence. Four more series of mounts occurred, each about 10 seconds in duration, with 18, 13, 10, and 15 thrusts during the mounting periods. In each case, the break occurred when the female either pulled away from the male or rolled onto her back, squealing. After a long burst of thrusting, the male will lick his phallus.
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Example of interaction and copulation by a male and female M. dobsoni with the female very receptive. Synopsis: Precopulatory behavior included nose to nose, nose to ear with the male following the female; the female paused to twitter, turned to the male; mutual gaping exhibited. At one point the male was gaping at the female and then moved his head to one side and demonstrated a nose to ear. This orientating toward each other, mutual gaping, and contact nose to nose, nose to ear, nose to nape, proceeded with interspersed driving for some 15 minutes. Finally, the male mounted, utilizing a neck grip. This was repeated for several rapid mounts terminating after a few thrusts whereupon the male dismounted. In one case the male fell to one side as he dismounted. Finally the male mounted for about 7 1/2 minutes. During the long mount, the male thrust at the rate of about 2 per second in bursts of 5 to 7 or 10. At the conclusion of the long mount, the male initiated driving again but the female turned to him and, exhibiting a gape or partial gape, repulsed him with twitters. The male persisted in driving, interspersed with brief mounts while thrusting at a rate of approximately 5 times per second. This sequence continued for some 20 minutes with intermittent chases. The male was removed as interaction apparently became more and more aggressive with the female squealing and fleeing from the male.
DISCUSSION
We would now like to explore in depth our analysis of the male-female interaction patterns displayed by Microgale dobsoni. During an encounter situation, initial contact would seem to be made by one animal approaching another and touching it somewhere on the body, perhaps the tail or the side, and then withdrawing or holding its position. The animal being contacted frequently turns to the contacting animal so that a nose to nose configuration occurs. This nose to nose configuration may result in a gaping reaction on the part of both animals with subsequent withdrawal only to reinitiate similar contact procedures or may be followed by contact promoting behaviors which further the familiarity of the two animals with one another. This would include naso-cloacal examination, perhaps by one animal, very often by both. If the encounter does not interrupt itself with agonistic behavior, such as the gaping reaction, then contact promoting behavior proceeds by further nasal investigation, generally nose to ear or nose to crown, nose to body, again naso-anal mutual, and finally, by grooming behavior. Grooming involves nibbling or mouthing the fur very often with the forepaws of one animal placed against the other's body holding it down somewhat. This may be displayed by either the male or the female. Reference may be made to Figure 29 which illustrates the major initial contact and contact promoting behaviors displayed by Microgale dobsoni. If contact promoting behavior proceeds without interruption, it may then pass on into sexual behavior.
Two types of sexual behavior may be noted, that which proceeds with very much resistance on the part of the female which in turn gives rise to a mixture of contact promoting behavior and agonistic behavior patterns. This would include the following types of interaction: Male attempting to mount while grooming and female exhibiting a gape reaction and jump away; or, while male stands with forepaws on female attempting to seek a neck grip, female rolls over on her back thus bringing her ventrum against the male's at right angles. In this position, the animals may begin to lock their forepaws about one another's body and tumble together while biting in a ritualized fashion at their fur, or the female, upon being mounted, may turn to one side and begin to groom the male. If the male rolls on his back, the grooming may continue. Grooming may have an aggressive character in that the female instead of gently mouthing the male's fur may actually pull pieces of hair out of the skin. An alternative to this would be where, upon being mounted by a male, the female may leap forward and move away. If she moves away slowly, and the male pursues, this can be termed a chase-flight reaction.
Mixed agonistic tendencies may not occur if the female permits mounting by standing and raising her tail somewhat. The male would then procced with his neck grip and begin to achieve intromission followed by thrusting. Thrusts occur in bursts of about 7 to 10 at a rate of approximately 2 per second. A burst of thrusts may be interrupted by the female rolling to one side or attempting to pull away from the male. If the female is exceedingly receptive, the mount, with bursts of thrusting, may be as long as 7½ minutes, as in one case. This long mount with continued bursts of thrusts is characteristic not only of Microgale dobsoni but also of all of the genera and species of the subfamily Tenrecinae which we deal with in subsequent sections.
The foregoing discussion indicates that receptivity on the part of the female varies. It is difficult to define an exact behavioral estrous response in tenrecs. Suffice to say that the female seems to show varying degrees of receptivity in part dependent on the season. During the nonbreeding season when the animals are obese, the tendency to mate may be vastly reduced and, after a brief agonistic interaction, the members may settle down in the same cage and tolerate one another. This would appear to be a period of anestrus. During the breeding season, the female shows varying degrees of receptivity and, indeed, by means of sustained encounter with the male, may be brought to a condition of full receptivity. We rather suspect on the basis of our limited observations that the female Microgale dobsoni is an induced ovulator and may show varying degrees of receptivity depending on ovarian condition which in turn is related to a cyclic physiological process more geared to an annual cycle than to a discrete estrous period which is more familiar to us with rodent studies.
Male-male interactions are typically concerned with the initial contact behaviors, followed by contact promoting behaviors, as in the male-female encounter, but these patterns generally lead to agonistic behavior. This results from the fact that one male or perhaps both will attempt to initiate sexual relations with the other male which are eventually broken off by the continued resistance from the more subordinate male. Strong resistance on the part of both animals leads to a general fighting behavior which includes locking and rolling, chasing, nipping, and fleeing.
Vocalizations seem to be of paramount importance during the encounter behavior of Microgales. The soft squeaking sound which has a dominant frequency from 3,000 to 6,000 cycles per second and has a chevron form is of moderately short duration and repeated. This sound often made by the male would seem to inhibit aggressive behavior on the part of the female and facilitate contact. In addition, it should be noted that the female may make this sound as well; it may serve a similar function to reduce agonistic tendencies on the part of the male. A series of louder squeaks which are typified by an inverted chevron pattern having approximately the same frequency range but being of shorter duration and repeated at a more rapid rate are characteristic of the female who is partially receptive but is exhibiting mixed agonistic tendencies towards the attention of the male. Similarly, if a male is being aggressed against by a female, his soft squeaks may grade into this squeak series which we have termed previously a twitter or trill.
In a defensive situation where the animal is facing out from the nest with the mouth partially open, a series of soft grunts may be given which have not been recorded but would seem to have lower frequencies involved rather than the high pure tones one finds in the soft squeak. A fully aroused animal defending itself against the approach of another will emit what has been termed a scream. This is a long sound being 0.3 of a second or more in length and being in general nonrepetitive. Although the dominant frequencies lie around 5,000 cycles per second, it is not as pure in tone as the soft squeaks or trill types. The aggressive buzz is similarly a nonrepetitive, noisy sound seemingly occurring at lower intensities than the defensive scream and often involved with an approach or attack motivation. Reference may be made to Table 4 for a physical analysis of the sound types produced by Microgale dobsoni.
Although we have discussed sounds used in encounters, we do not wish to underemphasize the role of olfaction. It should be pointed out again that during initial contact and contact promoting behaviors the nose is placed in areas of primary glandular secretion. Furthermore, nosing and licking these areas would insure not only that the responding animal was obtaining chemical information but further that the two animals by interacting in this manner serve to spread each other's scent upon one another. This is especially true of such behavior patterns as aligning the body axes and rubbing against one another or crawling over or crawling under. Such special attention to glandular areas in the form of ritualized contact configurations is characteristic of many other mammals.
The importance of our analysis of Microgale interactions cannot be overemphasized. In body form and in general ecology, Microgale probably represents a very close analog in form and function to the ancestral tenrec. The ancestral form for all the Tenrecidae was probably a small, furry, long-tailed insectivore which by adaptive radiation gave rise to the present day forms found on Madagascar. Some insight into the behavior patterns of Microgale is essential for delineating the core repertoire from which all other more specialized forms of tenrecids represent variations on a common theme. For this reason we should like to compare and contrast the interaction patterns of Microgale dobsoni with those of another insectivore somewhat conservative in body plan also, the house shrew, Suncus murinus (Family Soricidae).
Courtship and copulation in Suncus murinus.—Four pairings were staged to give us a range of variability. A given female exhibits a predictable tendency to mate after a certain amount of stimulation from the male. Several points of interest emerged during the observations, including: the female is highly defensive toward the male when he is placed in her cage. At the same time the male must explore the cage, sniff her defecation spot and mark before he settles down to attending the female. The male's attentions include orientating toward her and, during the initial phases, the female turns to him and wards him off either physically by a short rush, generally accompanied by a churring squeal, or by chirping loudly. The chirp components increase as the female becomes more and more prone to accept the male. The male, on the other hand, will turn away from the female and move off sometimes wriggling his tail and moving his rump from side to side as he moves away. This movement is reminiscent of the female's receptive movement which also includes a hip movement and tail waggle. The male will return and orient to and approach the female repeatedly and eventually the female becomes receptive and does not turn to face the male any more but begins to walk from him wriggling her rump and tail. At this point, the male generally attempts to mount. He apparently receives some stimulation from her wriggling tail as he attempts to mount. The mating act consists of a series of attempted mounts with or without intromission by the male. The male breaks off each time to wash his genitalia.
The mount series ends with a successful terminal mount including intromission and ejaculation. Immediately after ejaculation, the female refuses to accept the attentions of the male and returns to the original defensive activity, repulsing him, although the male may make repeated attempts to mount. If a second male is placed with the female, she will go through the original phases of defensive behavior but submit to being mounted again. Thus, the female will not often accept the same male twice in succession but may be induced to accept a second male. The marking movements by the male in her cage are quite evident and consist of rubbing the cheek and face as well as the perineal region at selected points in her cage. The female marks less than the male.
Note should be made of the following points after reading the Suncus summary. First, although the female eventually becomes receptive to mounting, she initially shows a pronounced agonistic tendency toward the male. The female, throughout the encounter, continues to squeak loudly at the male while keeping her body axis oriented directly toward his; mouth to mouth, nose to nose, mutual gaping and squeaking characterize the early phases, and it is only when the female begins to turn away from the male that the male attempts mounting. Mating behavior in Suncus consists of a repeated series of mounts with thrusting, concluding with a terminal mount resulting in ejaculation. In contradistinction to Microgale dobsoni, there is no long mount but rather a series of very short mounts with thrusting. Note again, in Suncus murinus that contact promoting behavior is reduced and occurs briefly after the female begins to show initial signs of receptivity. As in Microgale, it would appear that the activities of the male, with respect to the female, eventually trigger the female's full sexual response and nothing comparable to immediate lordosis, as seen in some of the rodents (e.g., Rattus norvegicus and Mesocricetus auratus), is to be found in these insectivores. Rather the participation of the male is essential in bringing the female into a full receptive state.
PARENTAL CARE BEHAVIOR
Two litters of three Microgale dobsoni were born and raised in captivity. Gestation has been estimated for one pregnancy at 62 days. Data on parental care are incomplete but the female builds a rather complex nest of leaves and paper strips within her nest box. The female will actively retrieve young which have been displaced from the nest by seizing the skin or body in her mouth and dragging or carrying the infant to the nest.
ONTOGENY OF BEHAVIOR
At birth the young are hairless except for the major vibrissae. The eyes and auditory meatus are closed. The tail is subequal to the head and body and measurements for the neonate are H.B. = 48 mm, T =29 mm. Growth becomes asymptotic at 50 to 65 days of age. The molt to adult pelage is complete at 95 days. The young begin to leave the nest to forage actively at 22 to 23 days.
SOCIAL ORGANIZATION
Judging from our trapping results, Microgale dobsoni does not exhibit any profound grouping tendency. The animals are well spaced in their environment and would appear to dwell in a solitary fashion. No tendency to form compact cohesive groupings can be discerned in our trapping patterns.
Other Species of Microgale
MICROGALE TALAZACI
Physical Description
Microgale (Nesogale) talazaci is the largest species of Microgale. It has a head-and-body length exceeding 100 mm with the greatest size in our series reaching 125 mm in length. The tail is slightly longer than the head and body, with a maximum measurement of 160 mm. The hind foot is approximately 21 percent of the head-and-body length, being some 20 to 21 mm in length. The dorsum is a very dark brown to almost black with the ventrum being a washed-out gray. The tail is uniformly colored. The extremes in captive weights ranged from 39 grams to 61 grams; however, this should not be interpreted as evidence for an oscillation in weight comparable to that displayed by Microgalc dobsoni. Actually, any given individual shows a remarkably uniform weight throughout the year. One male and one female, which we have been observing for two years, have shown less than 10 grams variation in weight throughout a given year. Average weights for a group of ten Microgale talazaci in captivity were between 50 and 60 grams (Figure 30).
The sexes are very similar in size and no pronounced dimorphism is discernable. The animals may be sexed only by expressing the phallus of the male from the cloaca, as described for M. dobsoni. Sex ratios in a sample of some 14 animals were approximately equal.
Distribution and Habitat
Microgale talazaci appears to be found in a broad strip from north to south in the true eastern rainforest region. We were able to trap the animals at two localities, Ambitolah and Perinet. At the collecting locality near Ambitolah, a pair was taken in adjacent traps on a small island formed by the deflection of a stream on either side of a rock outcrop. This area was very moist and located in a multistratal tropical evergreen forest habitat. In this same habitat Galidia elegans and Fossa fossa were trapped, and Hapalemur griseus and Lemur fulvus could be seen with little difficulty.
At Perinet a total of 18 Microgale talazaci was live-trapped in 539 trap nights. This species was taken in greatest abundance in those areas where neither Rattus rattus nor Suncus murinus were present. M. talazaci was taken as far as 240 feet from a stream on a hillside in rather dense multistratal tropical evergreen rainforest. They were also taken on the banks of streams and on the banks of lagoons which were overgrown with papyrus. In general, the animals were always trapped in association with reasonably mature second growth or multistratal primary tropical evergreen forest (see Figure 31). Although the animals were trapped on the ground, their behavior in captivity would indicate that they are able climbers; Webb trapped several in trees (BM 48108).
The soil in these tropical evergreen forest regions consists of a rich humus with some scattered leaf mold in the form of a thin layer on top of a red lateritic soil. Near the base of tree roots are to be found small burrows, 2 to 2.5 cm. across, and 1 to 1.5 cm. high. By digging in the soil, we have found that a given burrow may connect with tunnels which are under the topsoil and root “mat” which overlays the red, hard soil. It is assumed that these tunnel systems are used in part by M. talazaci.
The Annual Cycle, Reproduction, and Thermoregulation
Data concerning the timing of reproduction are very limited for this species. At Rogez a female with two embryos was taken in August and a lactating female was taken in February. Webb recorded two embryos each in two females on 22 October. Embryos were also noted in a 6 November collection (BM 48106, 4897, 48113). Captive births have occurred in March 1968 and July 1969. Weight changes in captivity indicate that, although M. talazaci is able to store some fat, there is no fat storage process comparable to that displayed by M. dobsoni. Furthermore, checks on thermoregulation indicate that M. talazaci tends to maintain a higher body temperature throughout the year than is the case with M. dobsoni. The lowest cloacal temperature for M. talazaci was 30° C. Cloacal temperatures in general ranged between 32° and 34° C. It would appear that M. talazaci, living as it does in a more stable environment, has not evolved semitorpor as a means of surviving extended dry periods as has M. dobsoni. This supposition is strengthened by the fact that M. talazaci does not accumulate fat in the manner described for M. dobsoni.
Feeding Habits
M. talazaci was tried with a variety of foodstuffs in captivity and it was found that they prey readily on a variety of insects, including coleopteran larvae and orthopterans and dragon flies. The animals may be easily converted to a raw chopped meat diet but are loath to take fruit.
Ethological Studies
GENERAL MAINTENANCE BEHAVIORS
Locomotion.—Microgale talazaci employs the crossed extension coordination pattern as its predominant mode of terrestrial progression. In addition it may exhibit the quadrupedal ricochet. The tail is generally carried off the substrate with varying degrees of tension in the tail reflecting different degrees of overall muscular tension in the subject. M. talazaci is an able climber and will spring from one branch to another. When climbing or moving about in the branches, the tail is frequently draped on a twig and the tip may be slightly coiled around a twig or projections in the bark, thus exhibiting some latent pre-hensility but in no way comparable to the prehensile tail of such an arboreal mammal as the mouse opossum, Marmosa.
Exploration and utilization of the living space.—As indicated under the section on habitat, the animals appear to utilize burrows. While engaged in live trapping at Perinet, we obtained more animals than we could utilize in our captive studies. As a consequence several of the captured animals were released from the traps at their capture site. Notes were made of their behavior. In one case, upon release a subject went down one of the small burrows previously described. As noted, such a burrow may connect with an extensive tunnel system under the thin humus and root “mat.” Other specimens when released crawled under a log or crept off through the leaf and grass litter on the forest floor. In one instance, a released animal ran along a well defined trail which was located along the edge of a bank approximately six feet from a path. One specimen was observed to jump from buttress roots to buttress roots, balance on a root edge, run along the length of a root, climb down, and then disappear into a burrow. When running along the surface of the ground and not under leaf cover, the animals kept the body close to the contour of the ground thus rendering themselves very inconspicuous before slipping away under leaves.
From these observations and those in our standard testing arenas (see Appendix C), we may conclude that these animals make versatile use of their habitat. They can forage on the ground very ably and remain quite inconspicuous. They are able climbers, but it would appear that a tunnel system in the soil offers some protection for them. In addition, regular pathways utilizing available cover in the habitat are employed by these animals.
Rest and sleep.—The postures and associated behaviors are similar to those described for Microgale dobsoni.
Marking.—As noted for M. dobsoni, this species marks by means of the perineal drag.
Care of the body surface.—The behavior is essentially the same as described for M. dobsoni.
Prey catching.—Behavior is essentially the same as that described for M. dobsoni.
Defensive and offensive behavior patterns.—As noted for M. dobsoni, M. talazaci will, upon being startled, flee or, if in the nest, will exhibit the open mouth threat (gape reaction). Occasionally when defending the nest it will produce a soft grunting sound with the mouth half open. Generally, during the gape reaction, it is silent or expels its breath in a soft hiss. Although unquantified it is apparent that M. talazaci is more aggressive than M. dobsoni and will vigorously defend its nest against any intruder.
SOCIAL BEHAVIOR
The patterns of social interaction displayed by Microgale talazaci are very similar to those described for M. dobsoni. One characteristic of M. talazaci, however, may be noted: males and females upon initial contact appear to establish a stable relationship with one another earlier than is the case with M. dobsoni. This may be evidence for a continued pair association on the part of M. talazaci throughout the annual cycle. By this, we do not mean to imply that the male in any way participates in parental care, but only that a given male and female may come to be familiar with one another and, indeed, utilize the same tunnel and burrow systems over a prolonged period of time. Our oldest pair of M. talazaci generally lost weight when separated from one another and reached a weight equilibrium when placed together again. A high degree of tolerance is shown between a pair of M. talazaci whereas male-male interactions and female-female interactions are characterized by avoidance or mixed agonistic tendencies.
Spacing and social organization.—Microgale talazaci cannot be said to exist in great density and do not form colonies. One pair of animals was trapped on consecutive nights at the same locus. Another pair of animals was trapped in adjacent traps. Two other pairs were taken 30 feet from one another and another pair at approximately 60 feet apart. Twelve specimens of the 18 collected at Perinet were taken at distances exceeding 1,000 feet from each other.
Development of young.—Two litters of one and two animals were bom to two females at the National Zoological Park. Gestation is estimated at 63 days. In growth and development this species parallels M. dobsoni. Measurements at birth for one specimen were: H.B. = 43 mm; T. = 27 mm; weight=3.6 gm.
MICROGALE COWANI
Physical description
Microgale cowani is a small tenrec with a head-and-body length of approximately 61 to 75 mm and a tail length of approximately 47 to 68 mm. The hind foot is about 15 mm in length. Thus, the tail is markedly shorter than the head and body and the hind foot approximately 21 to 23 percent of the head-and-body length. This would lead us to classify it as a surface foraging form. The weight ranges from 10.9 to 12.1 grams (see Figures 32 and 33).
The dorsal pelage ranges from agouti brown to black. One captive individual noticeably darkened at the conclusion of its first annual molt. Within a given series of specimens one can discern a variable tendency for the expression of a black middorsal stripe, but this pattern is not as pronounced as one finds in M. melanorrhachis. The ventrum in M. cowani is generally brighter in color than the dorsum and tends to be a gray-brown. The tail is correspondingly faintly bicolored.
Distribution and Habitat
This species has been widely collected in the eastern forest regions of Madagascar. Our particular specimen was captured in a grazing area approximately 3 kilometers west of Amparafara. The animal was trapped in an area of badly grazed-over land near second growth scrub. The discrete trap locus was in a tussock of grass. Other mammals in association with Microgale cowani were the insectivore Suncus murinus which was trapped about 50 yards from the locus of M. cowani.
General Remarks on Behavior
Our single living specimen of Microgale cowani exhibited the following noteworthy behavior patterns. It is extremely cryptic. Upon being placed in an open field testing situation, it shows no tendency to climb and makes use of all available cover, moving in a very cryptic fashion under leaves with the body pressed closely to the substrate.
The animal exhibits a typical face washing pattern as described for M. dobsoni and M. talazaci, i.e., sitting on its hind legs and stroking simultaneously with its forepaws on both sides of its head beginning behind the ears and carrying the stroke down to the tip of the nose. The mouth is held open during the terminal phase of the down stroke. The animal feeds on earthworms and was readily induced to accept a chopped meat mix diet. The animal will nest-build by carrying leaves into a nest box. Defensive behavior includes open mouth threat and biting. The chief characteristic of this species, when compared with Microgalc talazaci, would be its tendency to remain cryptic making use of all available cover in an open field testing situation and its extremely reduced tendency to climb.
- bibliographic citation
- Eisenberg, John F. and Gould, Edwin. 1970. "The Tenrecs: a study in mammalian behavior and evolution." Smithsonian Contributions to Zoology. 1-138. https://doi.org/10.5479/si.00810282.27
