Part 8

In the present study no incubation periods so short as those recorded by Noble and Mason, and Cagle, were observed. Incubation times were recorded for clutches both in the laboratory and in the field, but for most of the clutches only approximate incubation periods were recorded. Failure to record the exact date of laying or of hatching, or both resulted from attempts to avoid frequent disturbance of females in their nests, which might have caused them to desert.

One clutch of eggs laid in a terrarium probably on June 17, 1951--possibly a day or two earlier--hatched on July 30, after an incubation of about 44 days. Another clutch, found in a terrarium on July 17, 1951, was estimated to have been laid about a week earlier, judging from the average length (11.8 mm.) and average weight (.55 gm.) of the eggs. These eggs hatched on August 9, a little more than three weeks after their discovery. A clutch found in the field on June 25, 1951, evidently recently laid (average length 12 mm., weight .45 gm.), hatched 41 days later, on August 5. Another clutch found in a terrarium on July 17, 1951, was estimated to have been laid ten days or two weeks before, as the average length was 12.7 mm. The eggs hatched on August 7, three weeks after their discovery. On June 25, 1951, an incomplete clutch of three eggs was found with a female which still had an unlaid egg. The three eggs probably had been laid the same day or the day before. They were kept in the laboratory and weighed and measured at intervals until July 28, 33 days after their discovery when both those that remained were accidentally punctured and found to have nearly full term fetuses. In the field a nest which contained only a gravid female on June 24, 1951, had a clutch of eggs already mud stained and slightly enlarged on June 29. The most probable date of laying was June 26. On August 6 the eggs had all hatched but several young were still in the nest. Probably most hatched on August 5. The incubation time was hence approximately 40 days.

On June 21, 1951, a natural nest was found with eggs already somewhat enlarged (12.5 x 8 mm.) and mud stained. This nest was checked from time to time in the next few weeks, and after 39 days, on July 30, it was found that all the eggs had recently hatched, but six young were still in the nest cavity.

Another nest was found on June 24, 1951, with the eggs already markedly enlarged (14 x 8 mm.) indicating that laying must have been several days earlier--probably well over a week. Hatching occurred approximately 34 days later, probably on July 28, since on July 26 there was no sign that hatching was imminent, and on July 30 only the empty dried eggshells remained in the nest.

The incubation time approximated six weeks for those nests with most complete records. Under wet and stormy weather conditions such as prevailed in 1951, this may have been the normal incubation period, but in warmer and drier years incubation time is shortened.

In the five-lined skink each adult female normally produces one clutch of eggs annually. The size of the clutch produced is subject to individual variation, and is influenced by the age, size and condition of the female. Geographic variation in clutch size might also be expected. Data were obtained from breeding females killed and dissected, from counts of eggs found in natural nests in the field, and from clutches of eggs laid by females kept in captivity. For the total of 115 recorded clutches represented by the combined data from all these sources, the average number of eggs per clutch was 9.5.

In many females dissected for the purpose of obtaining egg counts, ovulation had not yet occurred. The ovarian eggs present in each of these females included two main size groups, the larger ones in process of maturing and evidently destined for deposition in the current season, and minute, immature ones. A few of intermediate size were always present, however, resulting in uncertainty as to the size of the clutch being produced, especially when development had not proceeded far. Even when the larger eggs formed a fairly distinct size group, some usually were well below maximum size. Relatively high counts of clutches were obtained from these examinations of enlarged ovarian eggs. Evidently development frequently is arrested, and resorption may occur before ovulation. As a result the numbers of ovarian eggs developing are a poor indication of actual clutch size. A series of gravid females were obtained and examined after ovulation; the numbers of eggs in their oviducts probably indicates accurately the sizes of their clutches. Gravid females taken from their nest burrows and kept in the laboratory in containers with loose damp soil soon excavated new burrows and deposited clutches. Many natural nests were found in the field, and the egg counts obtained from them provided further data concerning clutch size. Although most of these clutches probably had their full complements of eggs, others certainly had sustained losses to predators, or to the females themselves, which may eat some of the eggs. Therefore the average number found is erroneously low. Some of the natural nests found may have contained two or more clutches or parts of them, and the higher counts obtained from natural nests therefore are also questionable.

For different sets of data on clutch size, numbers were as follows:

Table 6. Size of Clutch.

=================+===========+============+===========+=========+========= | Number of | | Standard | | SOURCE OF SAMPLE| clutches | Mean | deviation | Maximum | Minimum -----------------+-----------+------------+-----------+---------+--------- Early ovarian | 25 | 11.4 +- .46 | 2.28 | 20 | 5 | | | | | Late ovarian, | | | | | uterine, or laid | | | | | in captivity | 56 | 9.16 +- .21 | 1.85 | 15 | 4 | | | | | In natural nests | 34 | 8.82 +- .32 | 1.85 | 16 | 4 -----------------+-----------+------------+-----------+---------+---------

On the average, larger females produce more eggs per clutch than do smaller females. Of 49 females for which measurements were recorded, and which had uterine or large ovarian eggs, 31 were 70 mm. or more in snout-vent length. These 31, mostly or entirely old adults, averaged 9.9 eggs per clutch, whereas 18 others that were 69 mm. or less in snout-vent length, and that must have been mainly or entirely newly matured adults in their first breeding season, averaged only 7.8 eggs per clutch.

Smith (1946:350) states that in the northern part of the range of this skink there is some indication of decrease in size of clutches. This is not well shown by published records. For the southern states, most of the published records of clutch size are by authors who did not clearly distinguish between the three kinds of five-lined skinks, and there is some doubt as to which species is involved in each record. For 56 clutches reported upon from north of approximately latitude 37 deg., I obtain a slightly higher figure than for 11 clutches from south of this line. Geographic trends are, of course, obscured by individual variation, and perhaps by abnormal clutches produced by individuals kept in captivity.

In Table 7, the figures marked with asterisks pertain to clutches that might have belonged to skinks of the species E. laticeps or E. inexpectatus since they were recorded in regions where laticeps and in some cases, inexpectatus also, occurs along with fasciatus. If these questionable clutches are excluded the remaining 55, definitely of fasciatus, average 8.48 eggs per clutch, whereas the 12 questionable clutches average 8.42. Both figures are close to the average of 8.82 +- .32 eggs for the 34 natural nests recorded in the present study. For the total of 1661 eggs of 182 clutches, from the combined sample of all available records for clutches found in the present study or reported upon in the literature, the average egg number is 9.13.

To sum up the available information on clutch size, the number of eggs is most typically 9, 10, or 11 and is more in large old females, than in small, newly matured females. In natural nests, even in those that are successful, there is often some loss of eggs, which are eaten by predators, or by the female herself, with the result that the egg counts made by various observers average somewhat lower than the numbers actually produced. The loss during incubation cannot be measured readily since it is almost certainly sharply increased by the disturbance entailed in observing nests. Exposing nests, even momentarily, for observation, may result in compacting of the surrounding soil, desiccation, temporary or permanent desertion by the female, and exposure to predation. Some indication of the incidence of loss during incubation might be obtained by counting and measuring the eggs in newly found nests and correlating numbers with size (indicating the length of time incubated).

Table 7.--Numbers of Eggs Per Clutch, Time of Occurrence, Laying Dates and Hatching Dates, as Reported in the Literature by Various Authors.

==========+==============+===============+=========+=============+==========+============= | Numbers | | | | | AUTHOR | of eggs | Date recorded | Natural | Laying date | Hatching | Locality | per clutch | | nest | | date | ----------+--------------+---------------+---------+-------------+----------+------------- Allard | 7* | .... | Yes | .... | .... | Northern | | | | | | Georgia | | | | | | Bishop | 8* | .... | Yes | .... | .... | Breathitt | | | | | | Co., | | | | | | Kentucky | | | | | | Blanchard | 9* | .... | .... | .... | .... | Tennessee | | | | | | Burt | 6; 11 | May, and | Yes | June 12, | .... | Douglas | | June 18, 1926 | | 1926 | | Co., | | | | | | Kansas | | | | | | Burt | 9*, 9*, | June 25 to | Yes | .... | .... | Arkansas | 9*, 10* | July 13, 1926 | | | | | | | | | | | | | | | | Ashville, Burt | 8* | June 6, 1933 | Yes | .... | .... | North | | | | | | Carolina | | | | | | Burt | 8* | June 28, 1934 | Yes | .... | .... | Scott, | | | | | | Mississippi | | | | | | Burt | 6* | July 7, 1933 | Yes | .... | .... | Emma, | | | | | | Georgia | | | | | | Burt | 6* | July 8, 1933 | Yes | .... | .... | Elk River, | | | | | | Alabama | | | | | | Cagle | Average | | | | | | 9.16 in 26 | | | | July | Elkville, | nests (6-15) | June-July | Yes | June 30 | 23-24 | Illinois | | | | | | Conant | 7, 9, 10, | | | | July 27, | | 11, 13 | .... | .... | .... | July 27 | Ohio | | | | | | Dunn | 12* | .... | .... | .... | Aug. 9 | | | | | | | Evans and | | | | | First | Arden, Roecker | 6, 7 | .... | Yes | .... | week of | Ontario | | | | | Sept. | | | | | | | Fitch | 9 | July 22, 1947 | Yes | .... | .... | Vernon (field | | | | | | Parish, notes) | | | | | | Louisiana | | | | | | McCauley | 3; 20 in 3 | | | | | | other nests | | | July 5 | August | | combined | .... | Yes | and 6 | 30 | Maryland | | | | | | Noble and | 2, 5, 5, | | | May 23, 27, | July 5, | Anderson Mason | 6, 7, 8, 8 | .... | No | 31; June 6, | 5, 6, 7, | Co., | | | | 6, 13, 20 | 9, 17 | Kansas | | | | | | Ruthven | 6, 6, 8, 9, | | | | | | 11, 13, 14 | .... | Yes | .... | .... | Michigan | | | | | | Smith | 9 | .... | Yes | .... | .... | Ohio ----------+--------------+---------------+---------+-------------+----------+-------------

BROODING

Lizards and snakes of several different families, are known to brood their clutches of eggs, although the great majority of oviparous forms do not do so. The brooding habit is perhaps best known in Eumeces fasciatus, and has been described by many authors. By far the most thorough account is that of Noble and Mason (1933) who observed and experimented upon seven females that laid clutches of eggs in captivity. These females, kept in separate terraria, excavated nest burrows for reception of their clutches, and remained with them throughout the time of incubation. There were three characteristic brooding postures; curved in a semicircle around the clutch, in an S-shaped figure extending among them, or lying straight, either over or among the eggs. The brooding females, taken quietly from their nests without disturbing them, were found to have temperatures averaging .4 deg.C. higher than the nests. Evidently normal room temperatures were maintained in the laboratory where the terraria were kept. The females occasionally left their nests, especially in late afternoon, to wander about the terraria, and to bask in sunlight. While basking, their temperatures averaged 2.7 deg.C. higher than the nest temperatures. The authors suggested that an important function of the brooding female was to transfer warmth from absorbed sunlight to the eggs. They state: "In nature the importance of the mother's body heat in the incubation of the eggs probably varies greatly with the type of nesting site selected." They suggest that in clutches deposited in logs or stumps beneath a thin layer of bark exposed to direct sunlight the need for warming by the female would be less.

My own observations do not support the idea that brooding by the female serves to hasten the development of the eggs. Both in the laboratory and in natural nests, clutches deserted by disturbed females hatched and the hatching was not unduly delayed. In the field, females were never observed to bask in the sun beside their nest burrows, and seemingly left them infrequently even to feed. When a female was caught in her nest burrow, her temperature nearly always approximated that of the surrounding earth with which she was in contact. The temperature in each nest depends primarily upon its situation. When the immediate vicinity of the nest receives direct sunlight, the eggs are warmed without the aid of the female, but when there is no sunlight the temperature is much lower. In order to maintain an appreciably higher nest temperature the female would have to make frequent trips to spots perhaps several feet or several yards away to find sunlight. Upon returning to the nest, her body heat would be quickly dissipated into the eggs and the surrounding damp soil. She would need to shuttle back and forth almost continually between the nest and a spot exposed to sunshine. Cloudy weather often preventing the warming of the eggs by absorption of solar heat prevails during much of the incubation season, in the region of the present study, and probably to an even greater extent throughout the range as a whole.

Noble and Mason state (op. cit.:9) that while in some non-brooding kinds of lizards the eggs are actually damaged by turning, the female fasciatus frequently turns her eggs and moves the whole clutch about in the nest cavity. On returning to their nests the experimental females each invariably touched one or more eggs with their tongues as an olfactory test. Eggs of other kinds of lizards not of the genus Eumeces, and shellacked eggs of fasciatus, or paraffin models of them, ordinarily were discarded immediately after a single touch of the tongue. Eggs of other individuals of the species, and even the eggs of Eumeces laticeps were accepted as part of the brood. Any of the experimental females would quickly retrieve one of her eggs moved a short distance outside the nest cavity. Even if the whole clutch of eggs were scattered about, the female would, over a period of hours, gather the eggs and return them to the nest cavity. This movement of the eggs is accomplished by rolling or pushing them in a loop of the body or tail, or, less frequently, by grasping an egg in the jaws, lifting it, and gently placing it in a new position. Even if the females were blindfolded, they were still able to retrieve scattered eggs, but one in which the tongue tip was experimentally removed showed no further interest in its eggs, presumably having lost the capacity to recognize them by olfactory test.

In the present study clutches unattended by females were observed to sustain heavy losses, both in the laboratory and in the field, and no doubt the attending female performs important functions other than that of warming the eggs. In the damp or wet nest cavity, the eggs tend to adhere to each other and to the earth walls and floor, and become sealed to such surfaces as a result of partial drying, reducing the amount of surface exposed to the air and probably hindering respiration. An eggshell sealed in prolonged contact with the soil tends to rot with the result that it is easily ruptured, and even if it is not broken there is the likelihood of fungi or microorganisms gaining entry and killing the embryo. In many of the eggs that were handled to obtain measurements and weight, rupturing of shells occurred. The shells are tough and elastic to the extent that even when eggs being handled were accidentally dropped on the floor on several occasions, no damage to them resulted. However, slight friction on the shell was sometimes sufficient to puncture one. Particles of sharp rock from the nest cavity may adhere to the shell, and result in rupturing, perhaps at weak spots where prolonged contact with the soil has caused deterioration. The female tends to keep her eggs in a compact cluster, shifting their position frequently so that no part of an eggshell adheres to its surroundings long enough for rotting to occur, and most of the surface of each egg is exposed to the air.

Another important function of the brooding female seems to be that of altering the nest burrow and shifting the eggs so that the effects of unfavorable weather are minimized. The usual response to warm and dry weather is deepening of the nest burrow. A cavity originally in loose soil on the underside of a flat rock, having the eggs in contact with the rock surface, may be displaced downward. The female excavates loose soil from the floor of the burrow and packs it on the top and sides, until the eggs are two or even three inches underground, in a cavity different in position and shape from the original one, although derived from it by gradual stages. In many instances, however, no such response to drying was observed. Probably extensive alteration of the nest burrow no longer is possible after drying of the soil has progressed beyond a certain stage as these skinks are not strong diggers. In some nests that were examined frequently, with resulting desertions by the attending females, the outlines of the cavities became indistinct and the soil around them became dry and packed. In heavy rains, when nest burrows are partly flooded, the females move the eggs to avoid their being submerged. The extent of the female's activity within the nest burrow is suggested by the glazed condition of the earth walls and floor, and by the mottled appearance which the eggshells soon acquire as a result of being slid and dragged about in the nest cavity.

Still another important function of the female is to dampen the nest burrow to prevent desiccation of the eggs. Even in dry weather, females taken from nests almost invariably voided water in relatively large quantities. They drink dew or other available water, and may void the contents of the bladder to moisten the nest cavity, as on numerous occasions, when nests were exposed by raising flat rocks covering them, part of the chamber was seen to be recently watered, and distinctly moister than the surrounding soil.

Noble and Mason (op. cit.:16-19) found that brooding females, in the laboratory, would vigorously defend their eggs against small enemies, including mice and lizards and the smaller kinds of snakes that were tested. The female watched alertly as the intruder approached, and attempted to bite it if it came too near or touched an egg. The females failed to defend their nests against persons and against a large blacksnake; when confronted with such a threat, the female would run from her nest cavity to hide. Cagle (1940:228) stated that the brooding females found by him stayed in the nests even when the logs in which they were situated were chopped open with an ax, and that the skinks would attempt to bite when touched with the finger.

In the present study, females whose nests were exposed never made any active attempt to defend them. Many darted away and hid as soon as they were exposed. In other instances, especially when the nest cavity was only partly exposed, from one side, the female cowered back against the inner wall, opening her mouth in threat if closely approached. If further molested she might then attempt to escape. In brooding females a tendency to sluggishness, and an affinity for the eggs delayed the usually speedy escape reactions. The temperature of the female was ordinarily lower than it would have been in the open or on the underside of a flat rock, and this also tended to slow her reactions. Gravid females when exposed in nest cavities that still contain no eggs are similarly sluggish and reluctant to leave differing little or none in behavior from those that have laid their clutches. Usually the female was found with her body encircling the eggs, holding them together in a compact cluster in the center of the nest cavity. The eggs rest in contact with the loose soil on the floor of the cavity, with each other, and with the female's body in the case of the outer ones of the cluster.

Normal brooding habits proved to be difficult to follow because the females were easily disturbed. In many instances those that had excavated nest burrows, but had not yet laid, deserted the nests after the disturbance involved in raising the sheltering rock. Females that had already laid before discovery of their nests were somewhat less inclined to desert, but many did so.

On numerous occasions, at the time of year when most females are gravid and are staying in nest burrows, I have discovered well formed nest burrows empty and seemingly deserted, with no female in evidence nearby. In some instances the female may have been out foraging or basking although she was not seen, and in other instances the female may have been killed by a predator or eliminated by some other accident. However, it seems that gravid females frequently do desert their original nest burrows, for one cause or another, and excavate new ones. Such desertions were noted many times in the females observed on the study area, where the disturbance from my own activities in raising the sheltering rocks may have caused shifts, but it was probably not the sole motivation. One female shifted approximately 120 feet, to excavate her second nest burrow in a site that was damper and more heavily shaded than the first site. This was in the notably dry summer of 1952. Most of the favorite sites under flat rocks in open situations, that were used in 1950 and 1951, were not occupied in 1952 or 1953, although several females did use them for original excavations, which were deserted before laying, as drought conditions developed. In the summers of 1952 and 1953 nests were difficult to find, and those discovered were on the average deeper and better protected than those found in other years.

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.