Part 6

SEASONAL OCCURRENCE

Collectors and other observers have often noted that reptiles, in general, are not found in equal abundance throughout the entire season of their activity. Many kinds are most in evidence within a period of weeks after emergence from hibernation, which corresponds with the time of breeding and later they become much scarcer. In skinks of the genus Eumeces this tendency is perhaps even more pronounced than in most other kinds of reptiles. By midsummer or considerably earlier their period of greatest activity is passed, and in some kinds, adults, or individuals of any size can rarely be found in the latter half of the growing season, even by a skilled collector familiar with their habitats and habits. Thus, Taylor (1936:5) in the preface of his revision of Eumeces, describing the difficulties involved in assembling needed series of the many Mexican species by collecting on summer field trips, wrote: "In 1934 in western Mexico ... I met with most disheartening results ... (although more than 1500 specimens were collected) only a single specimen of Eumeces was taken. Hobart Smith, in 1934, accompanied by David Dunkle, made a journey into northwestern Mexico ... and while generally successful, likewise obtained only a single specimen of Eumeces."

In the present study the tendency of E. fasciatus to concentrate its surface activity in early spring was clearly shown. In unseasonably warm weather in early spring, even in February in one instance, individual skinks have been found active on the surface or beneath flat rocks warmed by the sun; but general emergence ordinarily does not occur until sometime in April, depending on the weather. Unless the weather is much warmer than the seasonal norm, the skinks spend much of April in a torpid condition, either not becoming fully active until late in the month, or lapsing into torpidity with the return of cool weather after their first emergence from hibernation. During warm periods in April, however, activity is at or near its annual maximum for all individuals regardless of sex or age.

In May, with the advent of much warmer weather, daytime temperatures are usually high enough for the skinks to be active. Adult males travel about more actively and persistently than females or young, and as a result they are found so much more frequently that the numbers taken approximate those for adult females and young combined. Many of the adult males recorded in May were taken in funnel traps or pitfalls. Active males in the open were difficult to catch, and a high percentage of them escaped. To the casual collector or observer, these skinks are much more in evidence in May than at any other time of year, and most of those seen are adult males. By June, the numbers of skinks seen in the open decline abruptly. The adult males become relatively scarce, with reduction from more than half to about one-sixth of the total, and the young, about half-grown at that season, make up approximately half of the total. The adult females make up approximately one-third of the total June sample, but few of them were found active on the ground surface. Most were found in nest burrows beneath flat rocks. Under such conditions they tended to be sluggish in behavior, and were caught much more easily than were males and young. July was characterized by progressive decrease in the numbers of adult males, adult females, and second year young, whereby the numbers of each group were little more than half of those for June; and by appearance of a new crop of hatchlings which made up about one-third of the month's sample. Hatchlings first appeared from early July to late July in different years; few were recorded in July in some years. Females were much less commonly found in nests in July than in June because many nesting attempts were terminated before the beginning of July or early in the month, and probably because those that remained were often more deeply buried and better concealed. By August the adult males, and the second year young (by then approaching adult size) were found in still smaller numbers, but the number of hatchlings and of adult females approximated those recorded in July. In the females there is evidently some resumption of activity after the incubation period is terminated. The females are then hungry and sometimes emaciated, weighing less, on the average, than the year-old young of shorter snout-vent length. The numbers of hatchlings are augmented through early August in some years, as late broods continue to hatch. By early September few skinks except hatchlings are to be found, and activity continues to wane throughout the month. In October skinks of any age or sex group are a rarity, even though temperature is about the optimum for their activity. Little is known concerning where and how they spend the fall months. Probably they are not actually dormant, but retreat underground where temperature is moderate and humidity is high. Individuals kept in captivity at this season were listless showing but little inclination to feed. The only five-lined skink taken on the Reservation in November was found in a funnel trap after a rain at the end of a long drought. It may have been attracted to the surface by moisture.

The following table shows the dates on which various events of the annual cycle were observed in each of five different years. Owing, to the secretive habits of the skinks, these events generally were not observed until somewhat after their earliest occurrence in any one season. The lag was greater in some instances than in others.

Table 3. Phenology of the Annual Cycle in Five Different Years.

=====================+=========+=========+=========+=========+========= | 1949 | 1950 | 1951 | 1952 | 1953 ---------------------+---------+---------+---------+---------+--------- Earliest emergence | | | | | from hibernation | Mar. 30 | ....... | Mar. 24 | Mar. 29 | Mar. 20 General emergence | | | | | from hibernation | ....... | Apr. 7 | Apr. 14 | Apr. 17 | Mar. 27 Breeding coloration | | | | | appearing in males | ....... | Apr. 15 | Apr. 25 | Apr. 28 | Apr. 16 Peak of breeding | | | | | season | May 3 | May 12 | May 16 | May 10 | May 7 Females starting | | | | | nest burrows | May 26 | May 24 | May 19 | May 19 | May 24 Last appearance of | | | | | gravid females | June 10 | June 17 | June 29 | June 9 | ....... Earliest appearance | | | | | of eggs | June 10 | June 13 | June 24 | June 22 | June 16 Earliest appearance | | | | | of hatchlings | July 5 | July 15 | July 23 | July 3 | July 13 Latest hatching | | | | | date | July 15 | Aug. 8 | Aug. 8 | July 14 | ....... Latest fall record | Oct. 15 | Sept. 19| Sept. 26| Nov. 9 | Oct. 12 ---------------------+---------+---------+---------+---------+---------

SEXUAL CYCLES AND BEHAVIOR

Reynolds (1943:370 and 1947:191) studied the histological and gross seasonal changes in the reproductive organs of the adult male Eumeces fasciatus. There is a well defined annual cycle. "Early seasonal increase in seminiferous epithelial heights and in diameter of lumina and tubules reached a maximum in April followed by regression reaching complete involution by August. Late seasonal revival of activity results, by November, in size of testicular elements comparable to those seen in January. Primary spermatocytes predominate in the germinal epithelium in January, secondary spermatocytes and spermatids in February, with spermatids and metamorphosing sperm dominating from March until late June when the germinal material of the current season is exhausted." Fifty-three adult males were used as a basis for his study. These were of diverse origins from Arkansas, Florida, Missouri, Tennessee, and Indiana. Since sexual cycles in such widely ranging species tend to be synchronized with local phenology, and change somewhat from one region to another, the seasonal cycle may have been somewhat obscured by the diverse origins of the material. The Florida specimens may have been of the species E. inexpectatus. Apparently Reynolds' experimental skinks were kept in captivity for varying lengths of time before their reproductive organs were examined. The normal cycle would almost certainly be altered in captivity, especially in skinks kept at high temperatures during the time that they would normally be hibernating.

The seasonal change in gross appearance of the testes is not great. In the breeding season the testes are slightly enlarged and are firm and engorged, with pinkish or orange tinge. In immature males, and adults that are not in breeding condition, the testes are smaller, attenuate, paler colored, and flaccid. Sizes of testes in some males killed in the breeding season are recorded in Table 4.

Table 4. Sizes of Testes in Spring and Early Summer in Sexually Mature and Juvenal Males.

==============+===============+===============+=============== | Snout-vent | Sizes of | Age Date | length in mm. | testes in mm. | class --------------+---------------+---------------+--------------- May 6, 1951 | 76 | 7.0 x 4.0 | old adult May 20, 1951 | 77 | 5.0 x 2.8 | old adult May 20, 1951 | 74 | 6.2 x 3.2 | old adult May 20, 1951 | 74 | 5.5 x 3.0 | old adult May 20, 1951 | 66 | 5.0 x 2.8 | young adult May 20, 1951 | 65 | 4.2 x 3.2 | young adult May 20, 1951 | 64 | 5.3 x 3.1 | young adult May 20, 1951 | 45 | 2.5 x 1.0 | juvenile May 20, 1951 | 40 | 1.5 x .3 | juvenile June 3, 1951 | 65 | 5.0 x 2.5 | young adult June 10, 1951 | 67 | 4.0 x 1.8 | young adult June 25, 1951 | 75 | 4.0 x 2.0 | old adult June 25, 1951 | 70 | 3.5 x 1.8 | young adult June 25, 1951 | 51 | 2.0 x .5 | juvenile --------------+---------------+---------------+---------------

From the time of emergence in spring, males show some tendency to seek out females, and frequently a pair may be found together under the same rock, weeks before the onset of the breeding season. There is no satisfactory evidence that such associations have any permanence. At the time of emergence from hibernation the males rarely have even a trace of reddish coloration on their heads, and more than a month normally elapses before attainment of breeding coloration. Each year that observations were made activity of the skinks was interrupted by cold weather in April, so that the lizards were fully active for only part of the time between their earliest emergence and their attainment of breeding condition five to eight weeks later. The reddish suffusion of the breeding season, hardly showing in the first few weeks after emergence, appears suddenly within a few days in all adult males of the population. The best indication of the time necessary to attain breeding condition was provided by an adult male whose hibernation was interrupted on December 15 by bringing him into a warm room where he was kept at 80 deg. F. or more in the daytime, and approximately 70 deg. F. at night. Thirteen days later, on December 28, the male had developed a noticeable reddish suffusion. On January 3, nineteen days after hibernation terminated, the suffusion was near its maximum. When an adult female was placed with the male on this date, he showed sexual interest but the courtship was not consummated. On January 6, the 22nd day, the male's colors had reached their maximum, and when the female was placed with him, pursuit and copulation occurred promptly.

In the spring of 1952, the first skink of the season was found on March 29, still only partly activated, and under a large flat rock. Skinks were not caught or seen in any numbers until April 17, however, and general emergence probably occurred only a day or two earlier than this. On May 10, 1952, breeding activity was estimated to be at its peak. By May 28, the reddish suffusion was conspicuously faded in several males taken. By June 10 it was no longer discernible.

In the immature female the oviducts are small and threadlike, and the ovaries have grapelike clusters of pale whitish eggs, which are minute, often less than .5 mm. in diameter (Figure 8A). In sexually mature females ova enlarge rapidly after emergence from hibernation in the spring. While eggs are still in the ovary, they are approximately spherical. In late April and early May the developing ova enlarge rapidly. Approximate average sizes (dimensions in mm.) of developing ovarian ova in each of 22 mature females on different dates were as follows: April 17, 1949: 2.6, 2.3, 2.2, 2.2, 1.9, 1.9; April 18, 1949: 2.2, 1.9, 1.8, 1.1, 1.1; April 24, 1949: 4.6, 3.2, 2.5, 2.3; May 6, 1951: 2.5, 2.3; May 20, 1951: 7.0, 6.2; May 25, 1951: 8.0; June 3, 1951: 6.0, 5.5.

The two females containing ovarian eggs on June 3, 1951, were retarded individuals, taken along with several others that had already ovulated. Copulation takes place in early May before the ova have grown to their full size. In the following weeks both the ova and the oviducts enlarge rapidly. Upon passing into the oviducts, the ova assume an oval shape and are approximately 9 by 6 mm. before the albumen and shell are added. Deposition of a clutch of eggs probably extends over only a day or two at most, as clutches appear abruptly in the nest cavities. On only a few occasions were the females found in nest cavities with their clutches partly laid.

Sexual behavior is for the most part limited to a short period of weeks in spring. In an average year in the area of the study the first two weeks of May would include the peak and the greater part of the breeding season. The "courtship," such as it is, and mating have been described by many observers. However none of the published accounts seems to include all the essential features in their usual sequence as observed in the present study. It has been brought out by the studies of Noble and Bradley (1933:94), Noble and Teale (1930:54) and Schmidt (1933:71-76) that the sexual behavior of lizards has phylogenetic significance. Certain basic patterns in mating behavior are characteristic of saurian families, other traits are characteristic of genera, while certain details may be characteristic of species, or perhaps even of subspecies.

In the breeding season the adult male directs the greater part of his activities to a search for females, and finds them by both sight and scent. Observations on searching males suggest that they trail females by scent to some extent, or at least detect their presence in the general vicinity by this means. Upon discovering a female, the male pursues her with vigor and determination unless the temperature is too low, or unless he is not at the height of breeding condition. The female makes no positive response but reacts to the male's presence by fleeing, either frantically or perfunctorily, but if she is physiologically ready to breed the reaction is usually somewhat intermediate between these extremes. The first reaction of the male as he approaches the female is to touch her with his tongue, apparently receiving olfactory stimuli which are essential to the mating pattern. Rushing in pursuit of the female, he then attempts to seize her in his jaws. Most often a preliminary grasp is secured on the female's tail. The female may resist vigorously, wriggling and clawing, turning upon the male to bite or to threaten with her gaping jaws. At the first opportunity the male deftly shifts his grip from the female's tail or hindquarters to a more anterior position, which may be as far forward as the forelimbs or may be as much as an inch behind them, a little to one side of the mid-dorsal line. The male secures his hold by pinching loose skin into a small fold. Having gained this position the male is more or less out of reach of the female's jaws, and after a brief struggle both rest quietly except for their rapid breathing, usually for a minute or more, the ventral surface of the male resting on the female's dorsal surface. The male suddenly thrusts his tail beneath that of the female. His hind leg then rests over the base of her tail and the right angle formed by the laterally projecting hind leg and the tail in each lizard aids to guide their hindquarters into position so that cloacal contact is established. Copulation then begins immediately. The male's body may be bent in a semicircle, to one side of the female, or may be in an S-shaped loop, depending on whether or not the hemipenis employed is on the side opposite to that on which the female is grasped. Only one hemipenis is inserted, but occasionally the other may be everted also. As copulation begins the male's hind leg, flexed over the female's tail base quivers, but otherwise there is hardly any movement during approximately the first one-third of the copulatory period, and this phase may last for from one to three minutes. Then, abruptly, the male begins rhythmic, jerky flexions of the proximal portion of the tail, at the rate of approximately one per second. These tail movements are in a dorsoventral plane, and there is no perceptible movement of the body. Shortly after these movements cease, contact is broken usually at the initiative of the female, as she suddenly struggles to escape and is released either immediately or after a few seconds by the male. She then moves away, pressing her cloacal region against the ground. Her movements have become unhurried, with little or no attempt to avoid the male's attention. The male usually follows, either close behind, or straddling the female's tail or body. He may nip at her tail or body repeatedly, but without securing a grip. When the female pauses, he may come to rest with his chin or forequarters resting on her. Usually the association does not last more than a few minutes.

PLATE 1

PLATE 2

Noble and Bradley (1933:77) mention frequent homosexual matings between captive males. However, I observed no homosexual matings, either under natural conditions or in confinement. The pugnacious behavior of males that are in breeding condition ordinarily would prevent homosexual mating. Males in such weakened condition as to be unable to defend themselves effectively might evoke sexual attack, instead of the usual fighting response in other males. Although no actual experiments were performed in the present study in connection with the courtship and mating behavior, accounts of some workers seem misleading. My own observations indicate that the capacity for sex discrimination in this particular kind of lizard, and probably in others, has been underrated. For example, it has been stated that the male rushes with open mouth at the neck of any other skink that happens to be around, and he identifies it as a male if it fights back, or as a female if it does not. On the contrary my observations indicate that sex recognition occurs almost as soon as the male is aware of another skink's presence. The red head of the breeding male is an excellent example of a social releaser in the sense that this term was used by Tinbergen (1948:8). Like the red belly of the breeding male stickleback, it facilitates sex recognition and evokes hostile behavior on the part of other males. Courtship, mating, and fighting reactions however, seem to be evoked by the interaction of a complex of social releasers. Whereas males and females are strikingly different in appearance in the breeding season, visual sex recognition is complicated by ontogenetic changes. The body stripes characteristic of the female pattern, become dull or even disappear in some old females, which then approximate the typical male pattern. On the other hand newly matured males in their first breeding season retain distinct body stripes of the female pattern. Their sex is evidenced mainly by their reddish facial suffusion, which is not quite so extensively developed as it is in older individuals. Also, in these newly matured males the temporal region is not so swollen as it is in old males.

The male whose dormancy was terminated in early winter by bringing him into a warm room causing him to assume breeding coloration and to breed some four months earlier than those under natural conditions has already been mentioned. By the time the regular breeding season arrived, this male had long since undergone sexual regression and retained no trace of the red suffusion. In this condition, placed in a terrarium with a mixed group of breeding adults, his social status was of unusual interest. He exhibited no interest in the females and was less pugnacious toward other males than were the individuals in breeding condition. Although he seemed somewhat more nervous and timid, his hostile behavior was not entirely suppressed, as from time to time he moved up to other males and bit them viciously. His color pattern resembled those of certain old adult females in which the body stripes have been suppressed, but the breeding males evidenced no uncertainty as to his sex and were uniformly hostile. Their reactions were not noticeably different toward him than they were toward breeding males. The importance of an olfactory stimulus as a social releaser in sexual behavior of lizards has not been appreciated, although Noble and Mason (1933:10) did demonstrate its importance in the behavior of the female toward her eggs.

It is evident from published accounts, and from my own limited experience with fasciatus in parts of its range other than northeastern Kansas, that the phenology of the breeding cycle is subject to geographic variation, synchronizing with the somewhat different climatic conditions under which the species occurs. However, the difference is less than might be expected, in view of the species' extensive range. As a result of the early spring, and the warm summer climate in the southern states, dates of laying and hatching may be several weeks advanced. On April 12, 1952, Dr. Wilfred T. Neill showed me several live E. fasciatus, collected a few days before along the Trinity River in southeastern Texas, which appeared to be at the height of breeding condition. In northeastern Kansas on that date, general emergence had not yet occurred, and it was not until about May 10 that the population attained the peak of breeding condition. On May 8, 1948, near Burr Ferry, Vernon Parish, Louisiana, I caught an adult female in her nest burrow, and she contained eggs ready to be laid. Data with which Mr. Robert Gordon kindly provided me for specimens from southern Louisiana and southeastern Texas, in the Tulane University collection, indicate gravid females on June 4, 1952, and June 17, 1948 (3), and females with their egg clutches on June 16, 1948, June 17, 1948, June 23, 1950; and hatching dates in captivity of July 19, 1949, July 19, 1950, July 25-26, 1949. These dates correspond well with those for specimens obtained in northeastern Kansas in the same years. In the northern part of the range, Ruthven (1911:264) recorded that in the Saginaw Bay region, females taken on June 19 had eggs nearly ready to be laid, and after July 2 clutches were found frequently; young of the year were first observed on July 31. A juvenal specimen in the University of Minnesota Natural History Museum, collected on August 11, 1938, at Dresser Junction, Wisconsin, is 30-1/2 mm. in snout-vent length--approximately the size of juveniles in northeastern Kansas at the same season. Evans and Roecker (1951:6) record hatching as occurring in the first week of September at Arden, Ontario, indicating that at the northern edge of the range hatching may be delayed as much as two months. With such delayed hatching, but little time remains for the young to grow before they are forced into retirement for hibernation.

FIGHTING

Territoriality in the usual sense is lacking in the five-lined skink, and could scarcely exist in an animal of its habits. To defend a definite area (territory) against intruders of its own species, the animal would have to detect such intruders promptly. The skink, however, is so secretive in habits that at any given time the individual is likely to be hiding and inactive, even when conditions are favorable for it to be in the open, and other individuals therefore can then wander onto its home range unopposed. Even when an individual is active, it lacks the ability to detect others, except within a radius which would encompass only a small fraction of the entire home range. The senses are inadequate to inform one lizard of the presence of another until the two are only a few yards, or even a few inches apart. Usually the lizard is on the ground, where even small objects obstruct its view, and vision is probably effective for only a few yards. Hearing is probably effective for about the same radius in detecting animals of approximately its own size. Scent is effective in detecting prey near at hand or on contact, but probably does not serve for detection of other lizards that are not in the immediate vicinity. Therefore, the area covered by one in the course of its normal activities may harbor many others, and individuals most of the time are unaware of the others on their home ranges.

Under most circumstances these skinks behave toward each other with tolerance or indifference, but during the breeding season adult males become hostile, and fight on sight. Their reddish facial suffusion serves as a social releaser which elicits hostile behavior and facilitates sex recognition. As the breeding season wanes, the reddish suffusion fades rapidly and male hostility, probably controlled by the same hormonal complex, is likewise suppressed. Hostile behavior is rare in adult females or young at any time.

Combats and pursuits have been observed most frequently the last week of April and especially in the first two weeks of May. At this season funnel traps set along rock ledges often caught two adult male skinks together. In almost every instance one of the two confined males was mutilated, with pieces of skin and flesh bitten from the tail and with chin, snout, and neck scarred; most serious wounds were usually in the sacral region or base of the tail or both. Often the wounds were so severe that the skink died in a short time in captivity and presumably others that were released died also.

On April 28, 1949, a large adult male skink, chased by another, ran out in the middle of a trail and stopped. The pursuer stopped a few inches from it, then after a long pause, retreated in the direction from which it had come. For the five minutes that the pursued skink was watched, it lay motionless, partly hidden by dry leaves, evidently seeking to avoid further pursuit by concealment. I caught it without difficulty, and it seemed weak and dazed, as if injured in the fight. Its reddish suffusion was conspicuous, but not fully developed.