Part 12

Table 12.--Records of Individual Skinks Marked as Young and Recaptured Repeatedly After Attainment of Adult Size, Showing Trend of Progressively Slowing Growth.

=======+==================+==========+=====================+======+============================ | |Snout-vent| |Weight| | Date | length | Tail length | in | | | in mm. | in mm. | grams| Remarks -------+------------------+----------+---------------------+------+---------------------------- No. 1. |Male | | | |At an age of 33 months |April 12, 1950| 43 | 71 | 1.5 | this male was far short |August 30, 1950| 56 | 56 + 21 | 5.4 | of maximum size, and |May 23, 1951| 68 | 59 + 32 | .... | smaller than some |April 28, 1952| 73 | 62 + 38 | 6.6 | males a year younger; | | | | | all four captures within | | | | | a 65-foot diameter. | | | | | No. 2. |Male | | | |At an age of approximately |July 5, 1950| 61 | 92-1/2 (regenerated)| 5.2 | one year this |July 28, 1950| 64 | 97 (regenerated) | 5.4 | male was approaching |May 3, 1951| 68 | 96 (broken stub) | 5.8 | small adult size; when |June 21, 1951| 72 |101-1/2 (regenerated)| .... | last captured at an age |May 1, 1952| 78 |101 (regenerated) | .... | of 34 months, he was a | | | | | large adult. All five | | | | | records within a 190-foot | | | | | diameter. | | | | | No. 3. |Male | | | |This skink was nearly a |June 22, 1949| 65 |111 | .... | year old and nearing |May 4, 1950| 72-1/2 |115 | 7.3 | adult size when first |June 17, 1950| 73 |116 | 7.8 | captured; recaptured |May 15, 1951| 80 |125 | .... | in each of the four |May 13, 1952| 82 |125 | .... | succeeding years, he |April 6, 1953| 82 |104 (regenerated) | .... | showed slowing growth. | | | | | He was near the maximum | | | | | size at the time of his | | | | | last capture when he | | | | | was about 57 months | | | | | old, and evidently had | | | | | stopped growing (for | | | | | movement see No. 2, | | | | | p. 110). | | | | | No. 4. |Female | | | |This individual, marked |July 13, 1949| 27 | 34-1/2 | .... | when less than two |June 1, 1950| 54-1/2 | 93-1/2 | 3.1 | weeks old, had grown |August 21, 1951| 74 |119 | .... | to nearly the maximum |May 1, 1952| 76 |123 | 10.0 | female size at an age of | | | | | 34 months; all four | | | | | captures within a | | | | | 175-foot diameter. | | | | | (See Figure 24). No. 5. |Female | | | | |April 15, 1950| 43 | 70 | 1.4 |All six records within a |June 5, 1950| 52-1/2 | 87 | 2.8 | 65-foot diameter (See |May 25, 1951| 71 | 82 + 29 | .... | Figure 21). |September 28, 1951| 73 |111 (regenerated) | .... | |April 26, 1952| 74 |113 (regenerated) | 7.4 | |April 24, 1953| 76 |114 (regenerated) | .... | | | | | | No. 6. |Female | | | |Hatched in July 1949, |April 21, 1950| 46 | 75 | 2.1 | this skink had attained |May 7, 1950| 48 | 15 (broken stub) | 2.0 | the maximum female |May 3, 1951| 74 | 29 + 57 | 8.5 | size at an age of a little |May 2, 1952| 78 | 25 + 64 | .... | more than three years; |August 27, 1952| 79-1/2 | 95 (regenerated) | 8.3 | (for movement see | | | | | Figure 25). | | | | | No. 7. |Female | | | |Hatched in July 1949, |June 5, 1950| 51 | 82 | 2.5 | this skink was 11 |July 13, 1950| 59 | 93 | 3.9 | months old and about |July 29, 1950| 64 | 98 | 4.4 | half-grown when it was |August 21, 1951| 69 | 80 (broken stub) | 5.0 | marked. When last |May 28, 1952| 73 | 83 + 9-1/2 | .... | caught at an age of 35 | | | | | months it was of average | | | | | adult female size, | | | | | having grown less than | | | | | numbers 4 and 6 at the | | | | | same age. All five captures | | | | | were within a 60-foot | | | | | diameter (Fig. 24). | | | | | No. 8. |Female | | | |Hatched in July 1949, |April 26, 1950| 50-1/2 | 78-1/2 | 2.7 | this skink was of average |May 24, 1951| 74 |107 (regenerated) | .... | adult female size |April 28, 1952| 78 | 93 (regenerated) | 8.5 | and was breeding in |April 23, 1953| 80 | 93 (regenerated) | .... | May 1951; it grew | | | | | nearly to maximum female | | | | | size in the next 11 | | | | | months. All captures | | | | | within a 70-foot diameter. No. 9. |Female | | | | |July 5, 1950| 60 | 95 | 4.5 |All three captures at the |August 6, 1951| 71 |106-1/2 | 5.6 | same site. |May 28, 1952| 72 |110 | 8.5 | | | | | | No. 10.|Male | | | |Hatched in July 1949, |April 23, 1950| 46-1/2 | 66 (regenerated) | 1.8 | this male grew less |June 13, 1950| 52-1/2 | 26 + 3 | 2.7 | rapidly than most, and |September 2, 1950| 66 | 32 + 51 | 6.2 | in the spring of 1953 |May 29, 1951| 67 | 33 + 58 | .... | was smaller than some |August 3, 1951| 70 | 94 (regenerated) | .... | others that were a year |March 27, 1953| 74 | 78 (regenerated) | 7.1 | younger, or even two | | | | | years younger. No. 11.|Female | | | | |April 26, 1950| 50-1/2 | 78-1/2 | 2.7 |This skink had attained |May 24, 1951| 74 | 87 | .... | maximum female size |April 28, 1952| 78 | 72 + 21 | 8.5 | when she was a little |April 23, 1953| 80 | 73 + 20 | .... | less than four years old. -------+------------------+----------+---------------------+------+----------------------------

Differences in their growth rates therefore reflect differences in sex, individual vigor, and local situation, in individuals living at the same time and within the same general environment.

Changing weather, and other factors that vary from year to year cause marked differences in the dates of important events in the annual cycle, and in the stage of development at any given date. Data are available for five successive annual broods of young, those of 1948, 1949, 1950, 1951, and 1952, and each brood differs from the others to some extent, as shown in Figures 11 to 13. In 1949, for instance, young hatched relatively early, and probably most of them were active by the middle of July. They made rapid growth in August, averaging larger than young hatched in other years on any given date in late summer. However, they retired into dormancy early in the fall. Cool and dry weather in early September ended their activity for the season. In 1950, young hatched, on the average, at least three weeks later, about the first of August, but they remained active until late in September, and by hibernation time had partly caught up to the stage of development attained by the young of 1949. Most young of 1951 hatched late in the first half of August, and at first were smaller than those of 1950 and much smaller than those of 1949 on corresponding dates, but favorable weather in the early fall hastened their development. By early September they had caught up and passed the stage of development of young of 1950 and by the time they retired to dormancy in late September, they had reduced by half the size-advantage of the young of 1949 at the time these latter retired into hibernation. The young of 1951 appeared to be few in numbers, and a lack of competition may have been a factor in their rapid early development.

The young of 1948, first sampled after their emergence from their first hibernation in mid-April of 1949, were then somewhat intermediate in size as compared with those of 1949 and 1950 at the same times of year. Their subsequent development was rapid; by late May they had caught up and passed the stage reached by the 1949 young at the same time of year. The young of 1950 after having a late start, were further set back by cold weather in April 1951 delaying their emergence from hibernation. As a result they were still unusually small in late April and May. Even though they grew rapidly subsequently, they were consistently smaller than those of other broods on corresponding dates. Favorable fall weather prolonging the 1951 growing season into late September beyond the time of retirement in other years may have permitted many of them to attain adult size.

The varying fortunes of the several annual broods studied were closely correlated with weather trends, and suggest possible effects of slight changes in climate. An unfavorable sequence of weather might bring about drastic reduction of the population without causing any direct mortality. A late spring in two successive years would have cumulative effect in delaying emergence and breeding of adults the first year, and delaying in the second year emergence of the young, already retarded by the lateness of their hatching. If this sequence were followed by onset of unusually cool and dry weather in early September, or even in late August, the young might be "caught short," and forced to hibernate while still in the 50-60 mm. size class. Emerging the following spring, they might have failed to mature sexually, reducing by perhaps half the number of productive adults. At the northern extreme of the species' range, length of growing season may be more critical than extremes of temperature in limiting the numbers and distribution. Growing seasons that average long enough and warm enough to permit attainment of maturity by onset of the second hibernation period may be essential to the species. While no two annual broods of young in the same locality come under exactly the same weather influences, extremes of retardation or acceleration continuing throughout development are relatively rare. Retarding effects of unfavorable weather causing delayed breeding and hatching, may be offset by prolongation of warm weather in the fall thus delaying hibernation, or by warm spring weather hastening emergence from hibernation.

Under favorable conditions an adult female produces about ten offspring annually of which about half are females. It is calculated that if all survived, after ten breeding seasons, the progeny of an original female might have increased to a population of more than 97,000, under the climatic conditions of eastern Kansas, permitting attainment of breeding maturity late in the second year of life. In the same ten year period under climatic conditions delaying maturity until late in the third year of life (as seems normally to occur in E. septentrionalis and E. skiltonianus, and probably in E. fasciatus at the northern edge of its range) the original female would have produced a population of somewhat less than 7,800 assuming that all survived. With a long growing season such as occurs in the southern part of the range, it seems theoretically possible (though not probable) that individuals might mature before the end of their first year, in time to participate in the next breeding season. If this should occur the original female might produce a population of more than 120 million by the end of the tenth breeding season.

CHANGES IN PATTERN

Progressive alteration of the color pattern is more rapid in males than in females and is synchronized with growth. During the first year of life changes in the pattern are gradual, and consist chiefly of loss in vividness. The blue of the tail is slightly dulled. The light lines become suffused with brown and the dorsolateral dark areas become paler, with light brown areas appearing on the corners of the scales and gradually spreading to replace the original black. In skinks that are in the second year of life the striped pattern although still conspicuous is made up of two shades of brown instead of the earlier black and white markings.

Even in hatchlings, the dorsal part of the rostrum and the inter-nasals are of a somewhat neutral brownish color, matching neither the light lines nor the dark interspaces of the striped body pattern. With advancing age this neutral brown color gradually spreads posteriorly on the head so that the striking lyrate marking of the bifurcated dorsal stripe on the head in the juvenile become obscured by the time the skink has grown to small adult size, at 21 months. The top of the head is then dull brown, with a slightly mottled appearance caused by the different intensity of pigmentation in different areas. The stripes though still discernible, are faint and inconspicuous. Dorsally, on the body, the stripes are still conspicuous, but are dull and lacking in contrast. At this stage, the dark lateral area is retained with intensity of pigmentation scarcely diminished.

Table 13. Normal Range of Variation in Dorsal Striping of Head and Body, and in Color of Tail According to Age and Sex.

===================+================================+============================ | Condition of stripes | Color of tail Age, Size and Sex |-----+--------+----+-----+------+--------------+------------- |Sharp|Distinct|Dull|Faint|Absent| Original | Regenerated -------------------+-----+--------+----+-----+------+--------------+------------- Small young | | | | | | bright blue | bright blue body | X | | | | | | head | X | | | | | | | | | | | | | Larger young | | | | | | bright blue | duller blue body | X | | | | | | head | X | X | | | | | | | | | | | | Young adult female | | | | | | dull blue | gray-blue body | X | X | | | | | to brown head | | X | X | X | | | | | | | | | | Young adult male | | | | | | mostly dull | gray-blue body | | X | X | | | blue | to brown head | | | X | X | X | | | | | | | | | 3 year adult female| | | | | | mostly | mostly body | | | X | X | | brown and | brown and head | | | | X | X | gray with | gray | | | | | | scattered | | | | | | | blue scales | | | | | | | | 3 year adult male | | | | | | mostly | brown body | | | | | X | brown; | head | | | | X | occasional | | | | | | | bluish scales| | | | | | | | Old adult female | | | | | | brown; | brown body | | | X | X | X | occasional | head | | | | | X | bluish scales| | | | | | | | Old adult male | | | | | | brown | brown body | | | | | X | | head | | | | | X | | -------------------+-----+--------+----+-----+------+--------------+-------------

In tracing the gradual ontogenetic changes in the striped pattern, from the vividly contrasting colors of hatchlings to the dull, patternless coloration of old adult males, five descriptive terms have been applied to the successive stages: "sharp," "distinct," "dull," "faint," and "absent." To most individuals below minimum adult size, the term "sharp" is applicable, although there is some loss in vividness in the larger young, as compared with hatchlings. Fading of the original striped pattern proceeds more rapidly on the head than on the body. Upon emergence from their second hibernation at an age of about 21 months, the skinks, mostly grown to adult size, and ready to mature sexually, still show but little sexual difference. They retain the hatchling pattern essentially unchanged, but with colors dulled and contrasts reduced. Within a few weeks the newly matured males undergo relatively rapid color change as the breeding season progresses. The stripes tend to fade and blend into the dark areas adjacent to them. In the two-year-old males stripes are distinct to dull on the body and faint or absent on the head, while in females of the same age group, body stripes are sharp or distinct.

Table 13 refers to adult pattern and coloration as they appear in the breeding season. After the breeding season, in late spring and early summer, when the red suffusion of the head and neck has faded in adult males, the original striped pattern, after having been almost completely suppressed may again become discernible. Individuals of the same size differ in extent of pattern change, and the color descriptions made of individuals were not sufficiently detailed to show fully the changes occurring between successive dates of capture. However, most large adult males taken later than mid-June had at least some trace of the striped body pattern and many of them had become so much like females in appearance that close scrutiny was necessary to determine their sex. They were especially like females in having the dark lateral area extending forward onto the cheek and setting it off sharply from the paler temporal region above it. In breeding males the head has no such dark markings and is suffused with red.

GROWTH AND REGENERATION OF THE TAIL

Even among those skinks which have never broken their tails there is a wide range of variation in relative length of tail. This is partly a matter of relative growth since the proportions change during the course of development. Also there may be slight sexual difference and there is much individual variation. In fetuses still well below hatching size, the tail length is less than the snout-vent length. For instance, an egg in a natural nest 12 days short of hatching contained a fetus that had a snout-vent length of 14 mm. and tail length of 12 mm. (Figure 18). In the late stages of fetal development the tail growth is relatively rapid. At hatching, the tail is considerably more than half the total length. In a large series of young with snout-vent lengths from 30 mm. down to hatching size of 25 mm. or less, the tail length averaged 130.8 per cent of snout-vent length. In larger young, up to a snout-vent length of 40 mm. or more, the tail continues to lengthen more rapidly than the body. In skinks that are about two thirds grown, the tails average relatively longer than in either larger or smaller individuals. In the sample representing the size class 50-54 mm. snout-vent length, the tails average 163.3 per cent of the snout-vent lengths, whereas in groups of adults of various sizes and both sexes, the tail length is near 155 or 156 per cent of the snout-vent length. Sexual dimorphism in tail length is slight if it exists at all; in adult males, tails averaged a little longer than in adult females.

When a skink's tail is broken, there is almost no loss of blood. The fractured surface is rough and irregular, with exposed muscle masses protruding on the detached end and corresponding concavities on the end of the stump tail retained by the lizard. The concavities are soon filled with oozing blood, and a thick scab forms. As healing begins, the broken end presents a flat, slightly irregular surface. When the scab is sloughed off, a slightly convex surface of delicate, pale-colored new skin of the regenerating tail, is exposed. At first, no scale structure is discernible. As growth proceeds, the new tail takes on a bluntly conical shape. During the early stages of growth, it is well set off from the original portion by the abrupt taper at the point of contact and by its paler coloration and different texture, with no scales discernible at first, and later with fine and granular scalation. The new tail elongates until the more abrupt taper beyond the point of the break is no longer noticeable, and the coloration, surface texture and scalation match that of the original portion so closely that it is difficult to determine where the break occurred or even to ascertain that there has been one. On the regenerated tail, however, the scales are less uniform in size and less regular in shape. The regenerated tail, being different from the original in internal structure, with a cartilaginous rod replacing the vertebral column, is less fragile and subsequent fractures are most likely to be on the part proximal to the regeneration. Nevertheless, fractures of regenerated tails occur occasionally. In old skinks especially, the tail eventually may consist of three or more distinct segments including the basal remnant of the original tail and the successive regenerations. When a break in the regenerated tail occurs, the detached portion is relatively inert, and is capable of only feeble twitching movements in contrast with the lively wriggling normally displayed in a newly detached tail that includes part of the central nervous system.

Rate of growth in the regenerating tail is controlled by a variety of factors, such as age, condition, and activity of the individual, and site of the fracture. A break occurring early in the skink's lifetime results in regeneration more complete than occurs in an adult sustaining the same type of injury. The regenerated tail eventually may be longer and thicker than the lost part if the lizard is young and still growing. But the regenerated tail is never so long as the original one would have been. Regeneration is most extensive in those tails broken near the base. The farther from the base the break occurs the shorter is the part regenerated. As a result, tails that have had time to regenerate do not differ greatly in total length regardless of where the break occurred. However, the nearer the break is to the base, the shorter is the total tail-length after regeneration (Figures 19 and 20). If only the tip of the tail is lost, regeneration may not occur. In the skinks examined that had regenerated tails the proportions varied over a wide range. Presumably, in many, growth of the regenerated portion was still incomplete.

Table 14. Records of Regeneration of the Tail in Individual Skinks Marked and Recaptured.

=================+==================+==========+======================== | |Snout-vent| Age and Sex | Date |length | Tail length | |in mm. | in mm. -----------------+------------------+----------+------------------------ No. 1. |June 1, 1951| 73 | 38 (newly broken) Adult male |June 26, 1951| 73 | 38 + 14 |August 17, 1951| 76 | 40 + 45 |April 29, 1952| 76 | 40 + 45 | | | No. 2. |May 28, 1949| 51 | 46 (newly broken) Immature |October 15, 1949| 69 | 51 + 21 | | | No. 3. |June 11, 1950| 49 | 49 (newly broken) Immature |September 2, 1950| 63 | 63 + 31 | | | No. 4. |August 10, 1950| 62-1/2 | 60 (newly broken) Immature female|June 14, 1951| 68 | 62 + 17 | | | No. 5. |August 14, 1950| 67-1/2 | 77 + 4-1/2 Adult male |September 3, 1950| 68-1/2 | 77 + 6-1/2 |April 27, 1951| 69 | 78 + 9 | | | No. 6. |April 7, 1950| 67 | 38 (newly broken; Adult male | | | separated end 66) |July 27, 1950| 71 | 39 + 47-1/2 | | | No. 7. |May 28, 1951| 70 | 18 (newly broken; Adult male | | | separated end 100) |June 14, 1951| 71 | 18 + 1 |September 22, 1951| 76 | 19 + 29 + 7-1/2 | | | No. 8. |June 12, 1951| 72 | 33 (recently broken) Adult male |July 28, 1951| 76 | 36 + 31 | | | No. 9. |May 2, 1951| 45 | 47 + 1 Juvenile |May 14, 1951| 45 | 47 + 3 |May 19, 1951| 45 | 47 + 5 | | | No. 10. |June 7, 1952| 64 | 51 (recently broken) Subadult female|June 24, 1952| 64 | 51 + 11 | | | No. 11. |August 19, 1949| 42 | 40 (newly broken) Juvenile |June 13, 1950| 58-1/2 | 58 + 28 |August 5, 1950| 63 | 62 + 31 | | | No. 12. |May 17, 1951| 78 | 20 (newly broken) Adult male |June 12, 1951| 78 | 20 + 13 -----------------+------------------+----------+------------------------

Under favorable conditions regeneration occurs at a relatively rapid rate. After a period of healing the new tail grows with a sudden spurt, making most of its gain in length within a few weeks. Then growth abruptly slows or ceases altogether. In young similarly rapid growth of the regenerating tail occurs, but subsequently the increase is more gradual corresponding to the over-all growth of the lizard. In numerous adult skinks marked, and recorded as having well-regenerated tails, the proportions recorded at subsequent captures months or years later were still just the same, demonstrating that extent of regeneration is not proportional to elapsed time. Those adult skinks having unusually long regenerated tails presumably are individuals in which the original tail was lost early in life, and the potentiality for regeneration is probably somewhat less in older individuals, especially those that have stopped growing.

Successive records of selected individuals are listed in Table 14 to illustrate trends in regeneration of the tail. In those instances in which the tail is referred to as "newly broken" the separation usually occurred as an accident at the time the lizard was captured, while in those designated as "recently broken" separation had already occurred in some earlier accident but regeneration was not yet perceptibly underway. In the "Tail length" column, plus signs separate the original portion of tail, on the left, from the regenerated portion, on the right.

As in many other kinds of lizards, the tail in the five-lined skink serves as a reservoir for fat, which may be drawn upon for nutrition in time of food scarcity. An individual that is in good condition has a plump and rounded tail. Fat comprises much of its bulk. Upon emergence from hibernation this fat supply is not noticeably depleted. Brooding females in the latter part of the incubation period have the supply of caudal fat most noticeably depleted, and their tails may appear emaciated, with kinks on the terminal portion. It is my impression that in adults the capacity for storage of fat is most developed in the females, and that their tails vary in proportions more than do those of males. The capacity to shed the tail easily seems somewhat inconsistent with this function of fat storage. Loss of the tail sometimes involves loss of a large amount of reserve fat. Many detached tails that were broken accidentally at the time of the skinks' captures were weighed. In those that were broken off near the base and were not previously regenerated, weights were usually 16 to 20 percent of the lizards' total weights.

Movements

Data obtained concerning the movements of these skinks demonstrated that individuals tend to limit their activities to small areas thoroughly familiar to them, and wander but little. Although the nature and extent of movements in reptiles in general, and in lizards especially, are poorly known, my findings are perhaps what might be expected from the studies of earlier workers on various other species of reptiles.

Goin and Goin (1951:29) observed that Eumeces laticeps in Florida lives in hollow stumps, each individual excluding other adults from its stump but tolerating young. Movements have not been studied in detail in any member of the Scincidae, however. The observations of Goin and Goin, and those of other authors, seem to indicate that E. laticeps is territorial, and that each individual centers its activities about a tree or snag, regularly using the same hollow as a shelter and home base. In contrast, E. fasciatus is not territorial and has no regular home base.

The iguanid genus Sceloporus is perhaps better known than any other kind of lizard as regards its movements. Studies by Newman and Patterson (1909), Stebbins and Robinson (1946), and Fitch (1940) on three different species have shown that individuals of Sceloporus keep to small individual areas, and that territoriality is well developed, in some species at least.

Among other reptiles, turtles are much better known, as detailed studies of movements have been made on several species, of which the life histories and ecology have been thoroughly investigated (Nichols, 1939; Cagle, 1942 and 1944; Woodbury and Hardy, 1948; Stickel, 1950). They have been found to have well-defined and fairly extensive home ranges, which are not defended as territories. Studies of movements in several different kinds of snakes, by Blanchard and Finster (1933), Stickel and Cope (1947), Fitch (1949), Lowe and Norris (1950), and Carpenter (1952) have shown that these reptiles usually have definite home ranges, which may be several or many acres in extent. Their home ranges are not defended as territories against other members of the species. In general, turtles and snakes have been found to occupy home ranges that are much larger than those of lizards.