Chapter IV: Part 4

As compared with other North American lizards in general, _Eumeces fasciatus_ is notable for the relatively exposed and superficial situations chosen as nesting sites. However, it occurs in a climate of high humidity; in contrast, the great majority of our lizards live in arid climates where the eggs are in much greater danger of desiccation, and require better shelter to maintain the humidity at a sufficiently high level. Accounts in the literature and observations in the present study indicate that these skinks exercise a wide range of choice of nesting sites. Ruthven (1911:264) stated that in northern Michigan nests were usually in decaying logs; occasional nests were found in burrows in sand, but invariably decaying wood was present in or around at least part of the nest.

Blanchard (1922) mentions a nest in Tennessee that may have been made by either this species or _E. laticeps_ "in a hollow in a dead willow tree about fifteen feet from the ground buried in the loose, damp, rotted wood." Noble and Mason (_op. cit._:16) quote Blanchard (_in litt._) that in northern Michigan _fasciatus_ nests in logs that are exposed to sunlight. Conant (1951:31) stated that several clutches of eggs found in Ohio were an inch to six inches beneath the upper surface of the log or stump which sheltered them. Evans and Roecker (1951:70) record finding two incubating females inside rotten pine logs, in Ontario. Cagle, studying this species near Elkville, Illinois, in oak-hickory woods, found 25 natural nests of which three were in loose soil among the roots of a fallen tree, another was under loose bark of a log, and the remainder were all in cavities of partly decayed logs. Bishop (1926:119) recorded finding a female with a clutch of eggs beneath damp boards at Quicksand, Breathitt County, Kentucky.

In the present study, more than one hundred natural nests were found, of which just one (containing two clutches of eggs) was in decaying wood beneath the bark of an old log. All other nests were beneath rocks. On the University of Kansas Natural History Reservation, where most of the nests were found, the policy is not to tear apart decaying logs; therefore the nests probably present in such situations were not ordinarily found. On several occasions groups of hatchlings were seen on logs within which they probably had hatched. In the area of the study, however, decaying logs are scarce. The hardwood forests consist mostly of young trees that are second growth on cutover areas or pioneer on areas that were previously grassland. Because of frequent cutting there are few old mature trees, and logs have not accumulated on the forest floor. In northeastern Kansas, nesting in logs is comparatively rare. On wooded slopes and the edges of level hilltops, the flat limestone rocks that are often abundant provide preferred nesting sites. Even on collecting trips off the Reservation, where stumps and logs could be torn apart and searched, flat rocks were found to provide the main source of nesting sites. These nest rocks varied from less than an inch in thickness to nine inches or more, and from a few inches in diameter to three feet or more. Some were resting loosely on the surface of the soil and others were deeply sunken, on one side. Some were in situations exposing them to nearly the maximum amount of sunshine whereas others were in sites nearly always shaded. The varied character of the nesting sites chosen demonstrated a wide range of tolerance for temperature, moisture, and other factors, in the gravid and brooding female and in the developing embryo.

As already mentioned, Noble and Mason (_op. cit._:9-10) noted that females would accept and brood the eggs of other individuals just as readily as their own, and several writers have reported gregarious nesting habits, with two or more females occupying either the same nest cavity, or separate cavities that were in close proximity. For instance, Cagle wrote that among the small logs he found to contain nests, four logs each contained one nest, five each contained two nests, and two each contained three nests, while three other nests were found within an eight inch square area in loose soil among tree roots. McCauley (1939:93) in Maryland found three females brooding clutches of eggs, which totaled 20, and which were so near together that there was uncertainty as to which clutch certain eggs belonged in.

The gregarious nesting habit may be of benefit in permitting maximum utilization of choice nesting sites, where such sites are in short supply in an environment otherwise favorable. Also, the gregarious tendencies make possible more continuous guarding of the eggs against such natural enemies as can be repulsed by the female, since each female occasionally interrupts her brooding to bask or forage.

Many of the nests that I found were in close proximity to others. Often two nests, and sometimes even three, were found beneath the same rock, and sometimes a distance of only two or three inches intervened between the separate clutches. It seemed, however, that in almost every instance each female had excavated a separate nest chamber originally. In some instances adjacent nest chambers communicated with each other.

On July 13, 1948, a communal nest was discovered beneath loose bark of a decaying elm log. There were 22 eggs in the combined clutch, and there were two females in the vicinity. The bark was raised on several different days to examine the eggs, and one or both females always were found with the eggs.

On June 10, 1949, at the pond rock pile, a flat rock was turned and an unusual nesting aggregation consisting of a minimum of eight females, and probably more than ten, was found. The nests were somewhat disturbed by movement of the rock. The ground beneath was honeycombed with tunnels connecting the flask-shaped nest cavities, which were in part open to the rock surface on their upper sides. Clutches of eggs numbered 13, 12, 11, 8, and 6 (the last attended by a female which appeared to be still distended with several more unlaid eggs). Of five other females taken, two had laid and three were still gravid. Of the five clutches, two had eggs noticeably larger than those in the other three, and with their shells mottled brown from adhering earth. These nest cavities were about half an inch deep and two to three inches wide. The females were released as soon as they had been examined. One female moved about over the nest areas exposed, and evinced interest in a lone egg which had become separated from the others. She moved up to it, standing high off the ground, with her head turned at right angles to her body as if preparing to push the egg forward in the angle thus formed, and tested it with her tongue, but then she became alarmed and left the vicinity. The flat rock was lowered over the nests again with a minimum of disturbance.

On July 9, 1949, the flat rock covering the nests was raised again. Most of the eggs had hatched. Two broods of hatchlings were still in their respective nest cavities, and one entire clutch had not begun to hatch although its incubation was nearly completed. Three eggs of _Scincella laterale_ were found mixed with the _Eumeces_ eggs. One of these was opened to verify their identity; the other two hatched a few days later in the laboratory.

The following selected excerpts from my field notes, setting forth histories of several nests, so far as they were known, give some idea of the types of nesting sites chosen, the behavior of the females, and the hazards to which the eggs are exposed.

No. 1. At corner of pond rock pile.

June 21, 1951. Female escaped when rock was turned. One egg measured
12.5 × 8 mm., mud-stained.

June 22, 1951. Nest not in evidence when rock was turned; digging into loose
soil beneath to a depth of about an inch I exposed the eggs but did not disturb
them further.

July 23, 1951. When rock was turned, female did not attempt to escape, but
withdrew to far corner of nest cavity; when caught she voided a large scat
which seemed to consist mainly of _Ceuthophilus_ remains. Largest eggs in
the clutch were 18 × 10 mm. but two were noticeably smaller, and all were
heavily coated with dried mud.

July 30, 1951. Six young in the nest cavity, still not fully active; all of them
were heavily coated with dried mud.

No. 2. At hilltop ledge, under flat rock 13 × 10 × 1 inches, with
one edge sunken in soil; exposed to sunshine for most of day.

June 24, 1951. Female, snout-vent length 70 mm., tail 27-51, weight 5 gms.
Nine eggs, one of which measured 14 × 8 mm.

July 18, 1951. Nine eggs still in their original nest cavity, attended by the
female; she escaped into crevice behind the rock. The eggs were in slightly
damp soil, and in contact with the undersurface of the rock on their upper
sides; one egg was 17 × 10 mm.

July 26, 1951. Eggs caked with dried mud; still attended by female.

July 30, 1951. Dry and empty eggshells in nest cavity, evidently all the eggs
had hatched; no other trace of female nor of young; July 28th seems most
probable hatching date--if, on the 27th, some of eggs almost certainly
would have shown signs of hatching on the 26th when they were examined,
and if on the 29th some stragglers almost surely would have remained at
the nest on July 30.

No. 3. In small gully, on lower slope in hickory woods, beneath rock
9 × 9 × 1 inches, shaded by trees on south side for much of the day,
especially during latter part of morning.

June 24, 1951. The gravid female was deep in nest burrow.

June 29, 1951. When rock was lifted no trace of nest was visible except
for slightly disturbed loose soil at the point where it had been. When
some of this loose soil was cleared away, nest was revealed, with
11 eggs, mud-stained, approximately 12.5 × 8 mm. The female was cold
and sluggish, and did not attempt to escape, but cowered in the back
of the nest burrow, with jaws gaping; she was caught and marked.

July 20, 1951. Eight eggs remaining in the nest--two were accidentally
destroyed in moving them. These two were fertile and contained live
embryos, one of which measured 29 mm. in over-all length. One of the
remaining eggs was 16.5 × 10 mm. Female was present with the eggs.

July 25, 1951. Eggs still present in the nest cavity; female not in
evidence, but might have been concealed in corner of nest chamber as
it was not disturbed.

July 28, 1951. Female was again found with the eggs. One or more of the
seven remaining eggs were punctured in moving them during their
examination. Eggs about 16 × 10 mm.

August 3, 1951. Female was in nest with the eggs some of which are
slightly indented from drying.

August 6, 1951. When rock was turned, female darted out and ran to cover
about ten feet away. The eggs had hatched but two young remained in
the nest cavity, still rather slow and feeble in their movements and
not yet fully active. When routed from cover a second time, the female
ran back to the nest rock and took shelter beneath it.

No. 4. On upper slope above ledge, under a rock 18 × 9 inches, in
site shaded most of day; burrow nearly concealed beneath rock.

June 24, 1951. Nest occupied by a gravid female, apparently ready to lay.

June 30, 1951. Rock covering this nest has been undermined by a mole
tunnel, and many nearby rocks are undermined also. The eggs were
almost certainly destroyed by the mole's tunneling and may have been
eaten by it, since no remains are in evidence.

No. 5. At hilltop ledge beside old abandoned road, beneath flat
rock nine inches in diameter and about 1-1/2 inches thick, shaded
for first half of morning and most of afternoon, but exposed to
mid-day sunshine.

June 29, 1951. Standing water in bottom of nest chamber 1-1/2 inches
below underside of the rock. Some of the eggs are more than half
submerged. One egg is 14 × 8 mm.

July 21, 1951. Entrance of abandoned nest burrow has been enlarged by
running water channelled through in run-off during and after heavy
rains; shrivelled remains of eggs present at the bottom of the burrow.

No. 6. On grassy hilltop a few yards from ledge under flat rock,
9 × 6 × 2 inches.

July 23, 1951. Large female (snout-vent length 75 mm.) with three eggs,
16 × 22 mm.

July 27, 1951. Female escaped from nest cavity as rock was raised. Three
eggs were still in the nest, and a young skink was partly emerged from
one. A second egg not yet hatching was somewhat flaccid, 16 mm. long,
heavily coated with dried mud. The third egg much shrivelled, was opened
and found to have a dead fetus, perhaps a week short of hatching.

July 28, 1951. The flat rock which formerly covered the nest cavity was
found to have been raised and displaced, and no trace of the female,
eggs or young remained. Of possible predators that might have moved
the rock and destroyed the nest, skunk and opossum seemed the most
likely, but there was no definite clue as to the predator's identity.

No. 7. Two feet northeast of pond rock pile, under rock about one
foot square on upper surface with maximum thickness of about eight
inches, lying with upper side at 45-degree angle. The nest was under
one edge, with approximately three inches of rock over it. The rock
was exposed to sunshine throughout the day, except for grass shading
its edges.

July 23, 1951. When rock was turned, the female darted out of the nest
cavity, but in her dash to escape she dropped into a nearby pitfall.
When handled, she voided feces which contained the nearly intact shell
of a skink egg. Six eggs present in the nest; one selected as typical
was 11-1/2 × 8 mm. The eggs were slightly misshapen and might have been
damaged from drying.

July 26, 1951. When rock was raised, female darted out and escaped. The
six eggs still remained in the nest.

August 2, 1951. When rock was raised the female was not in evidence, and
only three eggs could be found; they had fallen from the nest cavity
to the bottom of the depression where the rock was imbedded and were
somewhat dried and indented.

No. 8. North slope, beneath rock approximately 18 × 15 × 4 inches,
at edge of small gully, where shaded most of the time including
mid-day hours.

July 20, 1951. Female attempted to escape from the nest. Four eggs
visible in nest, one 15-1/2 × 10 mm.

July 25, 1951. When rock was raised the female ran from the nest.

July 27, 1951. When rock was raised the female was in the nest with the
eggs; she ran and hid beneath a boulder five feet away. After a few
minutes she emerged and ran 15 feet to a hickory sapling and climbed
it.

July 28, 1951. Female was not in the nest but the four eggs were still
present.

July 30, 1951. Female found dead and partly eaten by ants beside rock
one foot from nest; eggs still present in the nest.

July 31, 1951. Eggs still present in the nest.

August 3, 1951. Eggs still present, including some deep in the nest
cavity which apparently were overlooked previously.

August 6, 1951. One much indented egg found outside the nest cavity was
opened and found to contain a live fetus, seemingly fully developed
and normal. The opened egg was placed on damp soil in a shady place
near the nest, but two hours later the hatchling had been killed and
partly eaten by swarms of ants.

August 9, 1951. The remaining eggs had disappeared, evidently taken by
a predator as no empty shells remained to indicate that the young
had hatched.

HATCHLINGS

Cagle (1940:229 and 232) has graphically described and illustrated the hatching of the five-lined skink, and numerous observations in the present study have served to corroborate his description. The first indication that the time of hatching is at hand is a twitching or jerking movement within the egg which continues until the shell is slit. According to Noble and Mason (1933:5) the shell is slit with the elongate premaxillary egg tooth which has its distal third bent forward nearly at right angles to its base. Some young remain for an hour or more with only the snout visible, however, once the head is extruded it is not again withdrawn unless the lizard is badly startled. The eyes are opened and blinked slowly, closed for a few minutes, and opened again. After the eyes have become adjusted, the fore-body emerges and the front legs are freed. In one clutch, observed by Cagle, hatching time for individual eggs varied from 45 minutes to five and three-fourths hours. If startled by visual or tactile stimuli, the little skink may lunge forward through the slit shell, with a sudden straightening of its body, and rush away for several inches. Its movements are slow, stiff and clumsy as compared with those of a skink that is a few days old and fully active. Hatching of a clutch ordinarily extends over 24 hours or more. Some of the young may be fully hatched and active before others from the same clutch have slit their eggshells.

Eggs ready to hatch ordinarily weigh somewhat more than one gram, up to at least as much as 1.7 grams, but much of this weight is made up of water absorbed during incubation. The hatchlings usually weigh from .2 to .45 grams. For each of two eggshells recently vacated, that were washed and squeezed dry, weights were approximately .125 grams. Hatchlings of the same brood differ perceptibly in size with several per cent variation in total length, and weight. Some seem to be less fully developed than others. On July 8, 1952, hatching of the last young in a clutch was observed. Upon emergence, it differed in appearance from the others of the brood hatched a few hours earlier. The top of its head bulged slightly as in fetuses. The umbilicus was not yet closed, and the protruding yolk mass hindered the hatchling's movements and made crawling difficult. In order to progress it had to stand high off the ground to prevent its ventral surface from dragging. Protrusion of the yolk mass has been described in newly emerged hatchlings for the closely related _E. anthracinus_ (Clausen, 1938:3-7) as well as in _fasciatus_. Cagle (_loc. cit._) states that the mass of yolk is at first about 3 mm. in diameter, but is completely used at the end of the third day. A group of young retained by him, without food, died the sixth day after hatching, seemingly from starvation. Three of five recently hatched young were found by Cagle to have eaten ant pupae placed in a box with them on the preceding day, even though the skinks still retained the yolk masses. One hatchling of this group ate its own tail that had been broken off in handling. Cagle described a color change taking place during the first few hours after hatching; the ground color, dull greenish at first, darkens to an iridescent black, the pale stripes are altered from an original tan color to bronze, with a tinge of reddish on the head, and the ventral surface which is partially transparent showing the outlines of the internal organs at first, soon becomes opaque white.

Contrary to the statement by Noble and Mason (1933:5) that in captivity the hatchlings seldom stayed together more than a few hours, litters of young fully active, a day or two after hatching were found in the nests with the females still looped around them on several occasions. On one such occasion, although the brood scattered immediately into surrounding vegetation where they hid, I succeeded in catching the female and six of the young, and put them all together in a nylon bag to carry them back to the laboratory. Several hours after the bag had been placed on a table it was noticed that the family had again gathered into a compact cluster in the bag with the female's body looped around the young in the characteristic brooding position seen in those with young or eggs in their nest cavities. When hatching is complete, the female may leave before the young have dispersed. On August 5, 1950, a nest under observation was found to have all of the young or most of them still clustered in the cavity, but the female was not in evidence. The young were active, and immediately took alarm as the rock was raised exposing them. Almost instantly, they scattered and vanished. Subsequent search revealed five of the young, each poorly concealed in tufts of grass or under dry leaves or other ground litter at the edges of the depression where the rock had lain. Once hidden, these young were reluctant to run again and depended on concealment.

Having once left the nest, the young probably do not return to it, as many nests examined within a few days after hatching were never found occupied either by females or young after their original dispersal. As soon as the dispersal occurs family ties are permanently severed. On July 19, 1950, a group of active hatchlings was observed moving about over a log, on what was probably the first day of activity away from the nest. The log was in the bottom of a steep-walled gully, where it had come to rest the night before. It had been an erect but dead and partly undermined snag on the edge of the gully, and was blown down that night in a violent thunderstorm. Most of the log was held clear of the rushing water in the bottom of the gully by projecting limbs. The little skinks were darting in and out of holes and crevices in the log, pausing frequently to bask. As many as four were in sight simultaneously, but probably the total included several more, as it was difficult to keep track of individuals. An adult female, presumably the mother of the litter was also present, but she took no interest in the young, and they showed no evidence of dependence on her. On the contrary, several times when one or another of the young happened to come near the female in the course of its wandering, and noticed her, it was seen to shy away in sudden alarm.

The young were much more active than the female. These and other young observed in the open were almost constantly in motion. Pauses to bask at any one spot were of only a few seconds duration. A certain log in Skink Woods evidently was the site of one or more successful skink nests each year that observations were made, although a nest was actually found in it only in 1948. On July 26, 1950, recently hatched young were active on this log. Temperature was about 22°C. and the young were alternating frequently between shade and sunshine to maintain their body temperature. Collectively they seemed to cover every square inch of the log surface, poking and probing into niches, crevices and insect borings. They had a tendency to seek out the highest points on the log as resting places.

In moving about, foraging or sunning, the young often carry the tail arched high, and keep it in motion with slow squirming undulations. These undulations may be continued even when the lizard itself has come to rest momentarily. The movements of the tail together with its vivid blue color serve to attract attention to it. Such behavior has not been observed in adults or partly grown young. Jopson (1938:90) observed an instance in which two dogs cornered a young five-lined skink (either the present species or _E. laticeps_) but were distracted by the wriggling of its bright blue tail "either dropped by autotomy or knocked off" so that the skink itself was allowed to escape. On another occasion these same two dogs attacking an adult male skink, were not distracted by the wriggling but dull colored broken tail, and they killed the lizard.

GROWTH

The subject of growth in _Eumeces_ was briefly discussed by Taylor (1936:66) in his revision of the genus. Sorting fairly large series of museum specimens into seeming age-size groups, Taylor concluded that skinks require as much as 9 or 10 years to attain adult size. For _fasciatus_, for instance, the snout-vent length of 65.7 mm. (small adult size) was considered typical of individuals in their ninth year of life, with yearly gain of only 6 or 7 mm. in length in the young. I have seen the original data on which this conclusion was based, and the age groupings, as assigned by Taylor, seemed plausible. However, in the light of present knowledge, it is certain that the seeming intervals between his assumed age groups would have disappeared with a still larger series of specimens. The eight or nine size groups that Taylor recognized as distinct annual age groups actually comprise only two age groups, each having such wide dispersion of individuals (by retardation of some and acceleration of others) that there is overlapping in size between them.

Growth in reptiles is now much better understood. Many species have been studied by a variety of methods, including observation of growth in captives, recording of growth in marked individuals living under natural conditions, and sorting of large series into age-size groups. Two species of _Eumeces_ have been studied in some detail. Breckenridge (1943:601-602) marked all the individuals of _septentrionalis_ that could be found in a small colony in Minnesota and he concluded from the growth recorded in several that were recaptured, that these skinks grow to mature size (65 mm. and larger) at the end of their second year of life and are ready to breed the following spring. Rodgers and Memmler (1943:61) plotted the size distribution of a large year-round collection of _skiltonianus_ from near Berkeley, California. They found that in this species hatching occurs in July and August, hatchlings are about 25 mm. in snout-vent length, and grow to about 50 mm. by the time they are one year old, and to about 65 mm. at two years of age, but most of them breed at the end of their third year. Within the genus the species _septentrionalis_ and _skiltonianus_ belong to groups separate from each other and from that including _fasciatus_. While _septentrionalis_ and _skiltonianus_ resemble each other in their growth pattern and in the time required to reach sexual maturity, _fasciatus_ is notably different in its more rapid growth and the shorter time it requires to reach breeding maturity. This would scarcely be expected, as all three are of similar size. Furthermore, _skiltonianus_ in the region of Rodgers' and Memmler's study has a longer growing season than _fasciatus_ in northeastern Kansas, while _septentrionalis_ in Minnesota has a growing season markedly shorter than either. It is noteworthy that each of these three skinks is the northernmost lizard in the section of the country where it occurs.

In the present study growth was investigated by measuring and marking large numbers of young, many of which were recaptured for subsequent records, and by sorting into age-size groups all available measurements. An understanding of the latter set of data was facilitated by correlating it with the growth records of marked individuals. Changes in the phenology of growth from year to year according to weather conditions were noted.

As already indicated, hatching occurs from early July to mid-August in northeastern Kansas. Unseasonably cool weather with frequent rains may cause cumulative delay in breeding and incubation so that hatching may average several weeks later than it does in years with relatively warm and dry weather during the breeding season. Within any one year hatching time is concentrated, so that the majority of the young hatch within a period of two weeks, but microclimates in the situations where the nests are made may differ enough to cause this much spread. Individuals living on north slopes in thick woods, and receiving the minimum amount of sunlight may have their emergence from hibernation and attainment of breeding condition delayed. Later, nesting in the same situations, they may have incubation of their clutches similarly delayed.

Newly hatched young average just under an inch in snout-vent length (23-27 mm.) and weigh .2 to .45 grams. Most rapid growth occurs in the period of weeks following hatching. The growth rate during this late summer period cannot be well shown by comparing average size of series taken on successive dates, because each series is likely to include some newly hatched young.

In 1949, a series of recently hatched young averaged 26.7 mm. on July 10. By August 26, average length in a series collected was 42.9 mm., indicating an average gain of at least .35 mm. per day. One that may be considered typical was marked on July 23, 1950, soon after hatching, and it had a snout-vent length of 26.5 mm. and weighed .25 grams. It was recaptured just a month later when it had grown to 36 mm. snout-vent length, and weighed .8 grams. Potential growth rate under favorable conditions is shown by the fact that some individuals have attained a snout-vent length of 50 mm. by the third week of August, thus approximately doubling their hatching length. A maximum growth rate of about .5 mm. per day is indicated for these accelerated individuals, but on the average, young are considerably less than 50 mm. in length even when they enter hibernation. At the other extreme, representing retarded growth, is an individual having a snout-vent length of only 34 mm. on May 1. It must have been approximately nine months old on that date, but of course had spent at least six months in hibernation. Even if it made rapid growth subsequently, this yearling could scarcely have attained by midsummer the pre-hibernation length of the most accelerated individuals.

During the growing season following their first hibernation period, the young grow to small adult size in most instances. After emerging from a second hibernation they mature sexually and constitute an important part of the breeding population.

Many of the skinks marked before their first hibernation, as hatchlings, when they were a few days or a few weeks old, were subsequently recaptured as well-grown yearlings or small adults, affording ample information as to the usual growth rate and the extremes of acceleration or retardation that occasionally occur. Records of selected individuals in this group of skinks, marked early in life and recaptured after a hibernation, are recorded below.

Table 8. Records of Individual Skinks Marked as Hatchlings (Before
the First Hibernation) and Recaptured the Following Year. Rapid
Rate of Early Growth Is Shown.

========+=================+==========+=====================+======+=============================
| |Snout-vent| |Weight|
| Date | length | Tail length | in |
| | in mm. | in mm. |grams | Remarks
--------+-----------------+----------+---------------------+------+-----------------------------
No. 1. |August 8, 1951| 23-1/2| 30-1/2 | .25 |Had just hatched when
|April 28, 1952| 39 | 55 + 1/2 | 1.3 |first recorded; second
|June 7, 1952| 48 | 69 + 1 | .... |capture was made soon
| | | | |after emergence from
| | | | |hibernation. All three
| | | | |captures within a 50-foot
| | | | |diameter.
| | | | |
No. 2. |July 8, 1952| 25 | 25 (broken stub) | .3 |
|April 23, 1953| 42 | 17 + 26 | .... |
|June 23, 1953| 56 | 22 + 36 | .... |
| | | | |
No. 3. |July 16, 1948| 26-1/2| 37 | .... |Caught at the same place
|July 5, 1949| 68 |101-1/2 | .... |on both occasions; in a
| | | | |little less than a year
| | | | |this female grew to
| | | | |small adult size.
| | | | |
No. 4. |August 23, 1950| 36 | 55 | .9 |The interval between
|May 19, 1951| 46 | 69-1/2 | 1.7 |captures included about
| | | | |two months of active
| | | | |life, plus the hibernation
| | | | |period; caught at the
| | | | |same place on both
| | | | |occasions.
| | | | |
No. 5. |September 2, 1950| 34-1/2| 33 (broken stub) | .... |Tail broken at first capture;
|June 12, 1951| 45 | 48 + 3 | 2.0 |recaptured 40 feet
| | | | |from original location.
| | | | |
No. 6. |July 28, 1949| 36 | 56 | .... |Recaptured 75 feet from
|April 21, 1950| 49 | 83 | 2.5 |original location.
| | | | |
No. 7. |August 31, 1951| 38 | 58 | .... |All three captures within
|May 25, 1952| 48 | 82 | .... |a 70-foot diameter.
|June 30, 1952| 63-1/2| 57 + 26 | .... |
| | | | |
No. 8. |August 23, 1950| 36 | 44 (broken stub) | .7 |Tail broken at first capture.
|July 23, 1951| 69 | 37 + 49 | .... |Capture sites 150
| | | | |feet apart.
| | | | |
No. 9. |August 23, 1949| 39 | 53-1/2 (regenerated)| .... |This male was retarded
|June 7, 1950| 46 | 70-1/2 (regenerated)| 2.1 |in growth, being still
|July 23, 1950| 58 | 88 (regenerated) | 3.7 |well short of small
|September 3, 1950| 62 | 91 (regenerated) | 4.9 |adult size as its second
| | | | |hibernation period
| | | | |approached; all four captures
| | | | |recorded within
| | | | |a few yards.
| | | | |
No. 10. |July 31, 1949| 38 | 23 (broken stub) | .... |Capture sites
|June 17, 1950| 58 | 43 + 36 | 3.6 |20 feet apart.
| | | | |
No. 11. |August 13, 1949| 40 | 66 | .... |Approximately a year
|August 8, 1950| 63 | 90 (regenerated) | 5.0 |after its original record
| | | | |this skink was recaptured
| | | | |80 feet away, still
| | | | |short of small adult
| | | | |size.
| | | | |
No. 12. |August 19, 1949| 42 | 40 (broken stub) | .... |All three captures within
|June 13, 1950| 58-1/2| 58 + 28 | 4.1 |a 50-foot diameter.
|July 5, 1950| 63 | 62 + 31 | 5.9 |
--------+-----------------+----------+---------------------+------+-----------------------------

Many other young were not caught and marked until the growing season following their first hibernation, and were recaptured within this second growing season weeks or months after they were originally marked, and after they had made substantial growth. Those recaptured near the end of this second growing season, when they were a year old, or a little more, usually had attained small adult size or were nearing it. Selected records of these yearlings are presented below.

Table 9. Selected Records of Individual Skinks Marked as Yearlings
(After Emergence From the First Hibernation) and Recaptured One
or More Times the Same Year. Rapid Growth Is Shown.

=======+==================+==========+=================+======+=================
| |Snout-vent| |Weight|
| Date | length | Tail length | in |
| | in mm. | in mm. | grams| Remarks
-------+------------------+----------+-----------------+------+-----------------
No. 1. |May 2, 1951| 38 | 53-1/2 | .... |Capture sites
|September 25, 1951| 62 | 25 + 31 | .... | 30 feet apart.
| | | | |
No. 2. |May 8, 1951| 39 | 57 | .... |Capture sites
|August 2, 1951| 60 | 67 + 25 | .... | 150 feet apart.
| | | | |
No. 3. |April 17, 1952| 39 | 55 | 1.1 |Capture sites
|June 23, 1952| 57 | 73 (regenerated)| .... | 30 feet apart.
| | | | |
No. 4. |May 20, 1952| 45 | 67 | .... |Capture sites
|May 28, 1952| 47 | 71 | .... | 15 feet apart.
|June 9, 1952| 53 | 82 | .... |
| | | | |
No. 5. |May 22, 1952| 48-1/2 | 77-1/2 | 2.0 |Capture sites
|July 20, 1952| 63 |106 | 5.3 | 10 feet apart.
| | | | |
No. 6. |June 11, 1950| 49 | 49 (broken stub)| 2.4 |Capture sites
|September 2, 1950| 63 | 63 + 31 | 4.9 | 20 feet apart.
| | | | |
No. 7. |April 14, 1950| 47 | 72 | 1.9 |Capture sites
|May 29, 1950| 50 | 82-1/2 | 2.5 | 50 feet apart.
| | | | |
No. 8. |May 12, 1952| 49 | 77 | .... |Capture sites
|June 18, 1952| 61-1/2 | 98 | .... | 60 feet apart.
| | | | |
No. 9. |June 4, 1950| 54 | 89 | 2.8 |Both captures at
|August 1, 1950| 64-1/2 |101 (broken stub)| 5.7 | same site.
| | | | |
No. 10.|June 11, 1950| 49 | 49 (broken stub)| 2.4 |Capture sites
|September 2, 1950| 63 | 63 + 31 | 4.9 | 20 feet apart.
| | | | |
No. 11.|June 13, 1949| 57 | 68 (regenerated)| .... |
|August 8, 1949| 70 | 37 + 11 | .... |
-------+------------------+----------+-----------------+------+-----------------

Adult skinks can be found in greatest numbers in the breeding season and many of the young that were marked were recaptured as newly matured breeding adults soon after their second hibernation, often still short of average adult size. Selected records of such individuals are presented below.

Table 10. Records of Individual Skinks Marked as Young and
Recaptured as Adults.

=======+===============+======+=====================+======+=========================
| |Snout-| | | |
| | vent | Tail length |Weight| Remarks
| Date |length| in mm. | in |
| |in mm.| |grams |
-------+---------------+------+---------------------+------+-------------------------
No. 1. |Male | | | |Probably less than a
|August 21, 1950|34 | 48 | .7 | month old at first
|May 30, 1952 |69 | 37 + 49 | .... | capture; at second
| | | | | capture 21 months
| | | | | later and 185 feet
| | | | | away, he had red
| | | | | facial suffusion
| | | | | already somewhat faded
| | | | | as the breeding season
| | | | | waned.
| | | | |
No. 2. |Male | | | |
|July 31, 1949 |39 | 64 | .... |All three captures
|August 22, 1949|47 | 75 | .... | within a 70-foot
|May 19, 1951 |73 | 69 (regenerated) | .... | diameter.
| | | | |
No. 3. |Male | | | |
|August 5, 1949 |36 | 57 | .... |Capture sites
|May 3, 1951 |67 |103 | 5.1 | 10 feet apart.
| | | | |
No. 4. |Male | | | |
|June 16, 1951 |44 | 41 (broken stub) | .... |Capture sites
|May 28, 1952 |63 | 77 (regenerated) | .... | 535 feet apart.
| | | | |
No. 5. |Male | | | |
|April 12, 1950 |45 | 73 | 1.9 |Capture sites
|May 1, 1951 |67 | 17 + 48 | .... | 100 feet apart.
| | | | |
No. 6. |Male | | | |This individual had
|April 12, 1950 |46 | 4 + 15 | 1.3 | attained approximately
|August 10, 1950|67 | 75 (regenerated) | 5.3 | average adult size by
|May 12, 1951 |71 | 77 (regenerated) | .... | the 1951 breeding
| | | | | season; all three
| | | | | captures were within a
| | | | | distance of 90 feet.
| | | | |
No. 7. |Male | | | |
|April 30, 1950 |48-1/2| 78-1/2 | 2.4 |
|June 15, 1950 |56 | 94 | 2.9 |
|May 19, 1951 |67 | 90 (broken stub) | .... |
| | | | |
No. 8. |Male | | | |
|May 3, 1950 |47 | 51 + 4 | 1.7 |Capture sites
|May 29, 1951 |75 |115 (regenerated) | .... | 450 feet apart.
| | | | |
No. 9. |Male | | | |
|June 2, 1949 |51 | 46 (broken stub) | .... |Capture sites
|May 2, 1950 |66-1/2| 31-1/2 + 51 | 7.0 | 90 feet apart.
| | | | |
No. 10.|Male | | | |
|May 20, 1950 |58 | 92-1/2 | 4.0 |Capture sites
|June 21, 1950 |61 | 95 | 4.7 | within 40 feet.
|August 21, 1950|70 |108 (broken stub) | 7.2 |
| | | | |
No. 11.|Male | | | |
|June 25, 1950 |62 |100 | 5.1 |
|May 1, 1951 |71 |113 | 7.1 |
| | | | |
No. 12.|Female | | | |
|April 15, 1950 |46-1/2| 73-1/2 | 1.5 |Capture sites
|May 20, 1951 |72 |113 | .... | 160 feet apart.
| | | | |
No. 13.|Female | | | |
|June 11, 1950 |51 | 69 | 2.5 |Capture sites
|May 25, 1951 |66 | 40 | .... | 20 feet apart.
| | | | |
No. 14.|Female | | | |
|June 6, 1949 |52 | 47 (regenerated) | .... |Capture sites
|May 20, 1950 |68-1/2| 69 (regenerated) | 7.5 | 20 feet apart.
|June 9, 1950 |71 | 71 (regenerated) | .... |
| | | | |
No. 15.|Female | | | |
|July 2, 1950 |60 |100 | 4.2 |Capture sites
|May 21, 1951 |74 | 33 + 35 | .... | 20 feet apart.
| | | | |
No. 16.|Female | | | |
|June 12, 1950 |57 | 83 | 3.1 |Capture sites
|May 1, 1951 |71-1/2| 53 (broken stub) | 6.4 | 35 feet apart.
| | | | |
No. 17.|Female | | | |This female probably
|June 22, 1949 |62 | 24 (broken stub) | .... | hatched in July 1948
|May 22, 1950 |72 | 27 + 7 | 9.0 | and was nearing adult
| | | | | size when first caught
| | | | | at an age of a little
| | | | | less than a year. By the |
| | | | | next breeding season it
| | | | | was an average sized
| | | | | adult; both captures at
| | | | | same site.
| | | | |
No. 18.|Female | | | |This female probably was
|July 4, 1950 |64 | 30 + 55 | 4.3 | Approximately a year
|May 23, 1951 |73 | 31 + 62 | .... | old when first caught,
| | | | | and she grew to average
| | | | | adult size by the
| | | | | next spring; both
| | | | | captures at same site. |
| | | | |
No. 19.|Female | | | |This female was about a
|July 5, 1950 |61-1/2| 92-1/2 (regenerated)| 4.7 | year old when first
|June 14, 1951 |73 |111 (regenerated) | 8.2 | captured; loss of weight
|June 29, 1951 |74 |106 (regenerated) | 5.0 | in July 1951 was caused
| | | | | by its laying a clutch
| | | | | of eggs. All three
| | | | | captures were within a
| | | | | 15-foot diameter. |
-------+---------------+------+---------------------+------+--------------------------

A certain small percentage fail to attain minimum adult size or breeding maturity by the time of emergence from their second hibernation. Among 77 individuals marked as young either soon after hatching or in spring and early summer, and recaptured the following spring, only one had failed to grow to adult size. It was 46.5 mm. in length when marked on June 13. When recaptured on April 25 of the following year, it had grown to a length of 59 mm., still short of minimum adult length. During the interval between captures it had maintained about the average growth rate. Its failure to attain maturity was obviously the result of its early retardation, and probably late hatching was primarily responsible. Although this is the only individual with known history, which failed to attain breeding maturity after its second hibernation, occasional specimens are taken in spring which are somewhat below adult size but seem too large to be young hatched the preceding summer. Obviously, the incidence of such failure from year to year would be influenced by weather conditions, and an unusually cool summer may result in such delayed laying and hatching that an unusually large proportion of young might fail to attain sexual maturity at the usual time. At more northern localities, the percentage of such failures might be expected to increase. At the northern edge of the range attainment of breeding maturity may normally require more than two years. Such delayed development would result in a drastic reduction of the reproductive potential which might be critically limiting to the species, even in an otherwise favorable environment, as the population would be unable to replace rapidly enough the individuals eliminated by normal mortality factors.

In contrast to the delayed development of those that have failed to attain maturity at an age of two years, is the accelerated development of those that have already more than doubled in length before the first hibernation, and continue to grow rapidly after emergence. By late spring they are already approaching adult size, perhaps even before laying has occurred, and while breeding is still in progress. It is certain that in northeastern Kansas there is no breeding by such accelerated individuals approaching adult size at an age of nine or ten months. Farther south in the species' range with a much longer growing season, there is perhaps some possibility of such early breeding by first-year individuals. This would reduce by more than half the length of time required for a generation, and would tremendously increase the reproductive potential. With such added impetus to its reproduction the species might be able to withstand greatly increased predation pressure, or other mortality factors.

Extremes of acceleration or retardation are relatively rare in the population studied. Nevertheless, in April there are some individuals between 50 and 60 mm. in snout-vent length which cannot be classified with certainty as to their age group, and might be either accelerated individuals about nine months old or retarded individuals about 21 months old.

The spread in size for any given age group is especially large, if data from different years are combined. A typical individual, having a snout-vent length of 25 mm. at hatching in mid-July may have attained 30 mm. by early August, 35 mm. by late August, and 45 mm. by the time it hibernates late in September. Emerging shortly before the middle of April it may grow to 50 mm. by the end of May, 58 mm. by the end of June, and more than 60 mm. by the end of July when it is a little more than a year old. By the time of its second hibernation it may have attained a length of from 65 mm. to 70 mm., and emerges from this hibernation as a breeding adult.

In reptiles in general there is a wide range in adult size, and the extent and rapidity of continued growth after attainment of sexual maturity and minimum adult size is still insufficiently understood. Information bearing on this problem was obtained in the present study from the recapture of marked skinks already measured as adults. It is evident that the growth rate of the young, amounts to as much as 15 mm. per month in snout-vent length in the late summer period from hatching until hibernation, averages perhaps three or four mm. per month in the summer after emergence from the first hibernation, and tapers off rapidly as adult size is approached.

One hundred of the skinks marked as adults or subadults and recaptured after intervals of months, including, in most instances, one or more hibernation periods, represent in the aggregate, 87 years of growth. These records show that after minimum adult size of 65 mm. is attained, growth slows abruptly, and that by the time a length of approximately 75 mm. is attained in most instances growth has become extremely slow in males and has virtually stopped in females. Males attain a maximum size several millimeters larger than that of females. Individuals differ greatly in their growth, however; some adults continue to grow rapidly till they near the maximum size, whereas others apparently stop growing when they are still below average adult size. Unusually large specimens are not necessarily old, but may have attained their size only a year or two after reaching maturity through the accelerated growth resulting from abundant food and predisposing genetic factors. Likewise, unusually old individuals are not necessarily the largest, but may be only a little above average adult size. It may be assumed that no growth occurs during the period of winter dormancy, which occupies approximately half the year in the population studied. To compute growth rates, in those recaptured after an intervening hibernation, periods of hibernation, arbitrarily estimated as six months, were subtracted from the time elapsed between captures.

Table 11. Average Growth Rate in a Selected Sample of Skinks
of Adult Size.

============+====================+====================
| Males | Females
|----------+---------+----------+---------
SIZE GROUP | Average | Number | Average | Number
|growth mm.|of skinks|growth mm.|of skinks
|per month |in sample|per month |in sample
------------+----------+---------+----------+---------
65-68 mm. | 1.4 | 11 | .8 | 12
69-72 mm. | .7 | 12 | .4 | 21
73-76 mm. | .7 | 13 | .3 | 21
77-80 mm. | .4 | 7 | .... | ....
------------+----------+---------+----------+---------

Opportunity to compare the rapid growth of young during their first year of life with the relatively slow continued growth after attainment of sexual maturity is afforded by the records of skinks caught and marked while yet immature and recaptured in two or more successive years after their attainment of sexual maturity. The records of selected individuals of this group are presented below. With the exception of number three, all in this series are of the 1949 brood, and probably all hatched within a two-week period.

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