Natural History of the Ornate Box Turtle, Terrapene ornata ornata Agassiz Part 10

In general, body temperatures approximated the temperature of the soil around the turtle. Body temperatures tended to be slightly higher than soil temperatures in November and December but were slightly lower than soil temperatures in the months of February and March. The lowest body temperature recorded for any turtle that survived a winter was 2.7 degrees, taken from an adult female on December 26, 1955. Body temperatures one to three degrees higher were common in the coldest part of the winter. Turtles in shallow hibernacula, like those observed in wooded areas at the Reservation, are probably subjected to freezing temperatures at least for short periods but I have no records of body temperatures this low, except where they were induced experimentally. Turtles exposed to temperatures of zero degrees or slightly lower would retain enough heat to survive without freezing for a period of several hours or even a day if well insulated. A temperature gradient exists within the body; cloacal temperatures, for example, differ from temperatures deep in the colon and temperatures in the dorsal and ventral parts of the body cavity (taken by manipulating the bulb of the thermometer while it was in the colon) differ from one another. Probably, therefore, some parts of some turtles--probably the top of the sh.e.l.l or the extremities--freeze in winter without causing the death of the turtle. Ewing (1939:91) found a female of _T. carolina_, just emerging from hibernation, that had lost some scutes from its carapace; he found the missing scutes in the hibernaculum and attributed their loss to severe temperatures in the winter of 1933-34.

The incidence of mortality due to freezing is unknown for most species of reptiles. The observations of Bailey (1948) on DeKay snakes (_Storeria dekayi_) and Legler and Fitch (1957) on collared lizards suggest that rates of mortality are high in dormant reptiles. Bailey (_op. cit._) suggested that winter mortality might act as a natural check on snake populations. Neill (1948a:114) thought more box turtles (_T. carolina_) were killed in Georgia by cold weather in late autumn than "... by all other factors together," and that this winter mortality acted as an effective check on population levels. Neill reported that many turtles left their burrows in late autumn and began to forage; if the temperature dropped suddenly, the turtles became "... too torpid to dig" and froze.

If ornate box turtles are occasionally caught in the open by a sudden cooling of air temperature, it would occur at a time of year when temperatures would approximate freezing but would drop not far below this level; laboratory and field records show that adults could probably survive these low temperatures overnight and warm up sufficiently on the following day to seek adequate shelter. Box turtles deepening their burrows in winter do so at body temperatures somewhat lower than 10 degrees (near the minimum temperature at which co-ordinated activity was observed in the laboratory); turtles found in the open in late October were known to burrow into the ground at body temperatures of approximately 15 degrees.

Emergence from hibernation usually occurs in April but in some years a few turtles may emerge as early as the first week of March. Emergence is stimulated by temperature and humidity. Fitch (1956b:438) stated that emergence was delayed until "... the ground has been sufficiently moistened and until air temperatures have reached at least 26." Box turtles at the Reservation emerged on April 21 in 1954 and from April 16 to 17 in 1955. William R. Brecheisen found recently emerged box turtles in Anderson County on April 2, 1955, and March 6, 1956.

Turtles were found facing upward in their hibernacula in early March.

As the temperature of the soil rises, they move slowly upward, usually following the route by which they entered. They remain just below the surface of the soil for a week or two before actually emerging; this final phase of emergence is probably hastened by spring rains that soften the soil. Activity may be sporadic after emergence if the weather is cold.

A number of box turtles at the Reservation emerged in a cold rain in 1954 when the temperatures of the air and ground were 16 and 13 degrees, respectively, but remained inactive for several days afterward. In 1955 the air and ground temperatures were higher (28 and 17, respectively) on the day of emergence and box turtles became active almost immediately.

DIET

Published information on the food of _T. ornata_ consists of a few miscellaneous observations. Cahn (1937:103) opened five stomachs that contained partly digested vegetable matter but no insects or other animal food: Ortenburger and Freeman (1930:187) noted that gra.s.shoppers were a main part of the diet of _T. ornata_ in Oklahoma and that turtles displayed unsuspected agility in catching them. Those authors also saw turtles eating caterpillars and robber flies.

Strecker (1908:79) stated that "The natural diet of this species consists of vegetable matter and earthworms." Norris and Zweifel (1950:3) observed the feeding habits of captive _T. o. luteola_.

Coyote melon (_Cucurbita foetidissima_) was eaten with reluctance but a collared lizard (_Crotaphytus collaris_) was quickly devoured.

Tadpoles of _Scaphiopus hammondi_ were caught in a small pool and eaten. Adults of the same species were rejected after being caught; box turtles were seen wiping their mouths after rejecting adult toads.

The authors suggested that _T. o. luteola_ is an important predator of _Scaphiopus hammondi_, since the two species occur together in many areas and the emergence of both is controlled to a large extent by rainfall. One individual of _luteola_ was seen eating a dead box turtle on a road.

Captive individuals of _T. ornata_, observed in the present study, ate nearly every kind of animal and vegetable food given to them. Table sc.r.a.ps, consisting chiefly of greens, various fruits and vegetables, meat, and cooked potatoes, formed the main diet of turtles kept in outdoor cages.

A number of persons have told me of ornate box turtles eating the succulent stems and leaves, and the fruits of various garden plants; similar incidents probably occur in areas of native vegetation. J.

Knox Jones told me he saw an individual of _T. ornata_ eating a spiderwort (_Tradescantia_ sp.) in Cherry County, Nebraska.

Sight-records of foods eaten by box turtles at the Damm Farm (excluding the many records of individuals foraging in dung or eating mulberries) were for gra.s.shoppers, caterpillars, and various kinds of carrion. Box turtles were often seen eating gra.s.shoppers on roads in early morning; Sophia Damm told me of frequently seeing individuals catching gra.s.shoppers in her garden. Ralph J. Donahue told me that on his farm in Bates County, Missouri, an individual of _T. ornata_ made a circuit of the lawn each morning in summer and ate all the cicadas (_Magicicada septendecim_) found.

Vertebrate remains found in the stomachs of box turtles seem to result chiefly from the ingestion of carrion. One box turtle ate a white egg (unidentified) that had fallen from a nest and another was seen with a blue down feather clinging to its mouth. Several colleagues have told me of box turtles eating small mammals caught in snap-traps and Marr (1944:489) reported a similar incident. J. Knox Jones told me he once found an ornate box turtle in the nest of a blue-winged teal in Cherry County, Nebraska; the three eggs in the nest had been broken. The only authentic record of an ornate box turtle preying on a vertebrate under natural conditions was one supplied by Ralph J. Donahue who saw an adult catch and eat one of a brood of bobwhite quail. In many areas where box turtles are abundant, it is the opinion of local residents that the turtles decimate populations of upland game birds by eating the eggs and young of these birds; these opinions result probably from rare encounters such as the one described by Donahue. I believe that box turtles at the Damm Farm were sometimes able to catch young frogs and tadpoles (chiefly _Rana catesbeiana_ and _R. pipiens_) at the margins of ponds. In autumn literally thousands of young _Rana_ were present in these places.

Ornate box turtles ordinarily attempt to catch and, without further examination, to eat, small objects moving on the ground, but are more critical of stationary objects. Captive turtles, for example, would immediately chase and seize a grape that was pulled or rolled slowly across a floor but a stationary grape was examined and then smelled before it was eaten. Similar observations were made a number of times with living and dead insects in the field and in the laboratory. A turtle discovering an object that is of possible value as food, approaches it closely, turns the head from side to side (presumably using the eyes alternately to examine the object), and then, with head c.o.c.ked at a slight angle, momentarily presses the nostrils against the object (Pl. 28, Fig. 4). If acceptable as food, the object is then swallowed whole or taken into the mouth with a series of bites; large insects are usually broken into several pieces in the process of being bitten and swallowed. Larger objects, such as dead vertebrates, are torn to pieces with the beak and forefeet before they are swallowed.

Hatchlings, when fed for the first time, ignored inanimate foods but eagerly chased mealworms, catching them usually by the anterior end.

The tendency of the young of certain species of turtles (especially captives) to be more carnivorous than adults is probably due to the a.s.sociation of movement with food; recognition of inanimate objects as food is presumably learned by older individuals.

Mulberries (_Morus rubra_), when they are abundant, const.i.tute all or an important part of the diet of ornate box turtles. On June 4, 1955, William R. Brecheisen and I drove along a road in Anderson County, Kansas, and stopped at each mulberry tree that we saw beside the road; we found at least one specimen of _T. ornata_ under nearly every tree.

Approximately twenty box turtles were collected in this manner in a little more than one hour. The heads and necks of most were stained dark-red from the fruit and, in some, nearly the entire sh.e.l.l was stained. Dissection of these turtles revealed that their stomachs were distended to two or three times normal size with mulberries; no other kinds of food were found in the stomachs. Some of the turtles voided purplish-black fluid from the cloaca when we handled them; the color of the fluid presumably resulted from mulberries.

Several turtles were observed through binoculars as they foraged.

Individuals snapped or lunged periodically at objects on the ground along the route of travel. Upon reaching an area where cow dung was abundant, a turtle would move directly to a pile of dung and begin tearing it apart with the forelegs or burrowing into it. Turtles most often foraged in cow dung that had a superficial, dried crust. The invertebrate fauna of older dung was probably greater than that of fresh dung. Adult and larval insects were eaten, along with quant.i.ties of dung, as they were uncovered. Sometimes box turtles chased and caught larger insects that ran a foot or more away from the pile of dung; the turtles could cover the distance of one foot with three or four quick steps. Depressions made by box turtles in cow dung, as well as drier cow dung that had been more completely dissected, were regarded as characteristic "sign" of _T. ornata_ at the Damm Farm and in other areas studied (Pl. 26). Several persons have told me of box turtles "eating cow dung"; these reports, most of them made by competent observers, probably result from observations of box turtles ingesting cow dung incidentally, along with some unseen item of food.

Contents of stomachs were a.n.a.lyzed. Scats and contents of lower digestive tracts, although obtained in large quant.i.ty, were unsuitable for a.n.a.lysis because of the fragmentary nature of the foods they contained. Relative amounts of various kinds of foods in stomachs were estimated; volume was determined by displacement of water or fine shot.

Twenty-three stomachs of adults were selected at random (except for the fact that empty stomachs were discarded) from more than a hundred specimens collected in Douglas County, Kansas, in the period from June, 1954, to June, 1957; the sample included stomachs obtained in nearly all the months of the season of activity. Kinds of foods in stomachs did not differ significantly in regard to the s.e.x of the turtles or to time of year. The stomach of each of two juveniles (included in Table 6) contained a greater variety of animal food than did the stomach of any adult, but no kind of animal was eaten by the juveniles exclusively.

Each of the 23 stomachs contained animal matter and, in addition, all but two contained at least some plant material from dung, which const.i.tuted up to 20 per cent of total stomach contents.

Insects were present in each of the 23 stomachs and const.i.tuted the bulk of the animal matter; beetles, caterpillars, and gra.s.shoppers (ranked in descending order) were the kinds occurring most frequently and const.i.tuting the largest average percentages of total stomach-contents. Most of the beetles were scarabaeids and carabids; the bulk of the caterpillars were noctuids and arctiids. Gra.s.shoppers, with one exception, were of a single species, _Melanoplus differentialis_. It is noteworthy that two of the kinds of insects frequently eaten (differential gra.s.shoppers and noctuid caterpillars) are of economic importance in that they damage crops.

TABLE 6.--Kinds of Animals Found in the Stomachs of 25 _Terrapene o.

ornata_ of Both s.e.xes (23 adults, 2 juveniles) from Douglas County, Kansas. Frequency of Occurrence (number of stomachs in which found) is Given for Each Item Listed.

=======================================+============================= | FREQUENCY OF OCCURRENCE |--------+-----------+-------- | Adults | Larvae | Total ---------------------------------------+--------+-----------+-------- Gastropoda | | | _Helisoma_ sp | 1 | | 1 _Succinia_ sp | 1 | | 1 _Polygyra_ sp | 1 | | 1 _Retinella_ sp | 1 | | 1 ---------------------------------------+--------+-----------+-------- Crustacea | | | _Procambaris gracilis_ | 1 | | 1 _Armadillidium vulgare_ | 4 | | 4 ---------------------------------------+--------+-----------+-------- Orthoptera (Locustidae) | | | Locustinae (_Melanoplus | | | differentialis_) | 13 | | 13 Oedipodinae | 1 | | 1 | | | Lepidoptera (unspecified) | | 1 | 1 Arctiidae | | 9 | 9 Noctuidae | | 10 | 10 Pyralidae | | 1 | 1 Sphingidae | | 1 | 1 | | | Diptera (Sarcophagidae) | | 1 | 1 | | | Coleoptera (unspecified) | 3 | | 3 Cantharidae | | 1 | 1 Carabidae (unspecified) | 6 | | 6 (_Eumolops colossus_) | 1 | | 1 Cerambycidae (_Prionus fissicornis_) | 1 | | 1 Chrysomelidae | | | (_Diabotrica 12-punctata_) | 1 | | 1 Curculionidae (_Calendra parvulus_) | 3 | | 3 Lampyridae (_Photinus pyralis_) | 2 | | 2 (_Photuris sp._) | | 1 | 1 PhenG.o.didae | | 1 | 1 Scarabaeidae | 11 | | 11 | | | Hymenoptera (Formicidae) | 2 | | 2 ---------------------------------------+--------+-----------+--------- Phalangida | 1 | | 1 | | | Araneida (_Epeira_) | 1 | | 1 | | | Diplopoda | 1 | | 1 ---------------------------------------+--------+-----------+--------- Vertebrata (carrion) | | | 4 ---------------------------------------+--------+-----------+---------

TABLE 7.--Occurrence of Insects, by Frequency and Volume, in Stomachs of 23 _Terrapene ornata_ from Douglas County, Kansas. Relative Volume is Based on Total Amount of Food Material Present, Excluding Stones and Vegetable Material Contained in Dung.

===================+=========+=============+==============+========== | Insects | Orthoptera | Lepidoptera |Coleoptera | (all) | | (larvae) | -------------------+---------+-------------+--------------+---------- Average | | | | volumetric | | | | percentage | 88.6 | 28.7 | 26.9 | 32.5 -------------------+---------+-------------+--------------+---------- Range | | | | (volumetric | trace | | | percentage) | to 100 | 0 to 100 | 0 to 100 | 0 to 100 -------------------+---------+-------------+--------------+---------- Frequency of | | | | occurrence | | | | (percentage | 100 | 52 | 65 | 74 of total stomachs | | | | in which found) | | | | -------------------+---------+-------------+--------------+----------

Snails, sowbugs, and the one individual of crayfish found in stomachs were kinds that could be expected to occur in moist gra.s.sland or in wooded stream courses. Mulberries were present in one stomach and fragments of bird's-nest fungi (_Cyathus striatus_) were present in another. Carrion consisted of remains of mammals and birds; the only identifiable items were bones of the eastern cottontail (_Sylvilagus florida.n.u.s_) and a chicken. Stones up to seven millimeters in diameter were found in many stomachs; stones const.i.tuted as much as half of total stomach-contents. Presumably the stones were accidentally swallowed when food was taken from the ground.

The few adequate reports on dietary habits of _T. carolina_ (Allard, 1935:325-326; Carr, 1952:147, 150, 152, 153; Stickel, 1950:361; Surface, 1908:175-177) indicate that the species is omnivorous but that individuals tend to be herbivorous or carnivorous at certain times. Ornate box turtles resemble _T. carolina_ in being opportunistic feeders but rely on insects as a staple part of the diet. In this respect the ornate box turtle seems to differ from all other kinds of box turtles in the United States and it is probably unique in its habitual utilization of dung communities as a source of food.

POPULATIONS

Ornate box turtles were probably more numerous on the Damm Farm than any other kinds of reptiles, excepting skinks (_Eumeces fasciatus_ and _E. obsoletus_), and were by far the most conspicuous element of the reptilian fauna.

The 194 box turtles that were marked at the Damm Farm were captured a total of 437 times. Seventy-nine (41 per cent) individuals were recaptured at least once, 49 (25 per cent) twice, 29 (15 per cent) three times, and 20 (10 per cent) were recaptured at least four times.

Only three individuals were recaptured more than eight times. The greatest number of recaptures for a single individual, an old female, was 23.

In all, 185 turtles (95 per cent of total recorded at Damm Farm) were captured on the pasture. Of these, 73 were in the northwest corner area, 44 in the house pond area, and 35 in the southern ravine area.

The density of the population at the Damm Farm, considering the entire area, was .88 turtles per acre; for the woodland area alone, density was .41 turtles per acre and for the pasture alone, density was 1.49.

Acreage and population density in the northwest corner, house pond, and southern ravine areas were respectively, 28 acres with 2.6 turtles per acre, 7 acres with 6.3 turtles per acre, and, 17 acres with 2.6 turtles per acre. The densities noted above for the wooded area and for the entire Damm Farm are low as a result of incomplete sampling in the wooded area. Estimates of population density for the subdivisions of the pasture seem more closely to approach the true population density in areas of favorable habitat.

Fewer unmarked turtles were captured as the study progressed, but they were still being captured occasionally when field work was terminated.

In order to estimate the number of turtles in the population at the Damm Farm the "Lincoln Index" (Lincoln, 1930) was used to compare the ratio of marked individuals to total number of individuals (17:56) in collections for June, 1956, to the ratio of marked individuals as of July 31, 1955 (87) to total individuals in the population; the result was 286.

Fitch (1958:78) estimated the population of _T. ornata_ in one area of the Reservation (including woodland and ungrazed pasture) to be .076 turtles per acre. Stickel (1950:373) estimated the population of adult _T. carolina_ to be four to five turtles per acre in favorable habitat at the Patuxent Research Refuge, Laurel, Maryland; juveniles comprised less than ten per cent of the population.

Of the 194 turtles marked at the Damm Farm, 103 (53 per cent) were adult or subadult females, 61 (31 per cent) were mature males, and 30 (16 per cent) were juveniles of undetermined s.e.x. The ratio of males to females was then, 1.00 to 1.69, and the ratio of juveniles to adults was, 1.00 to 6.47. Eighteen of the 194 individuals were juveniles less than 90 millimeters in plastral length and only six had plastra less than 60 millimeters long (Fig. 25). The unbalanced ratio between males and females may result, in part, from s.e.xual differences in habits. The studies of Carr (1952:9), Fitch (1954:140), Forbes (1940:132), Legler (1954:138), and Risley (1933:690), have shown, however, that unbalanced s.e.x ratios, with females outnumbering males, are found in several species of reptiles, especially in turtles.

Records for 540 adult _T. ornata_ collected at the Damm Farm, the Reservation, and on roads in eastern Kansas, show that females outnumber males just before and during the nesting season and again in late autumn (Fig. 26). The high incidence of females in May, June, and July, can be explained by their more extensive movements a.s.sociated with nesting in these months. I have no explanation for the increased number of females captured in late autumn. In April and August, the only two months in which males were more abundant than females, the samples were small. The number of juveniles collected was too small to allow any trustworthy conclusions concerning their seasonal incidence; a few juveniles were taken in nearly all the periods in which adults were active.

Risley (1933:690), studying _Sternotherus odoratus_ in Michigan, found an over-all s.e.x ratio of 1.0 male to 2.3 females; the percentage of females in collections ranged from 50 to 71 per cent in April and most of May and rose to 83 and 85 per cent in late May and mid-June, respectively.

The infrequency with which hatchlings and small juveniles of ornate box turtles are observed is well known to naturalists. Several of my colleagues who are expert field observers and who have lived in areas where ornate box turtles are abundant, have never seen hatchlings; many other persons have seen only one or two. Rodeck (1949:33), noting the abundance of coleopterous insects in the scats of captives and the rarity of individuals of all age groups during dry periods in Colorado, commented, "It is possible that the young are even more subterranean than the adults. Perhaps they spend their early years in rodent or other burrows where there is a fairly abundant insect fauna.

Increasing size might force them to the surface for feeding, with a daily return to a burrow for resting and protection."

[Ill.u.s.tration: FIG. 25. Composition of the population of _T. o. ornata_ at the Damm Farm based on the 194 individuals marked there in the years 1954 to 1956. Individuals smaller than 100 mm. ordinarily could not be s.e.xed accurately and are shown as open bars. Open bars in the groups larger than 100 mm.

are for females, whereas solid bars are for males.]

My own experience in the field has shown that small examples of _T.

ornata_ are not so rare as previous workers have believed. Small box turtles occupy the same microhabitat as do the adults and seem not to be more aquatic or subterranean in habits. Juveniles are found in burrows, in marshy areas, and in other sheltered places, but so are adults. Most of the juveniles that I found were in open situations where adults were abundant, sometimes within several inches of a place where an adult was feeding or basking. Nearly every one of the smaller turtles was discovered when I was closely scrutinizing some other object on the ground; sometimes juveniles were actually touched before being seen. Most juveniles were covered with cow dung or mud and blended so well with the substrate that they were detected only when they moved. It is likely that only a small number of the young box turtles present in an area is ever actually observed. Young are more vulnerable to predation and injury because of their small size, soft sh.e.l.ls, and immovable plastra. They evidently rely, to a large extent, on inconspicuousness for protection.