Natural History of the Ornate Box Turtle, Terrapene ornata ornata Agassiz Part 11

[Ill.u.s.tration: FIG. 26. The seasonal abundance of females of _T. o. ornata_ based on 540 adults captured at the Damm Farm, the Reservation, and on roads in eastern Kansas, in the years 1954 to 1956. Records are grouped in periods of 30 days, the periods beginning with the dates shown at the bottoms of the bars. Juveniles are not considered. Numbers at the top of each bar indicate the size of the sample (both s.e.xes) and give an approximate indication of relative seasonal abundance of adults, except for August, when little field work was done.]

MOVEMENTS

The only previous study of movements of _T. ornata_ is that of Fitch (1958:99-101). He recovered 14 marked _T. ornata_ at the Reservation a total of 30 times, the period between recaptures varying from one to seven years. He reported that the average radius of home range was 274 feet (for an area of approximately 5.4 acres), excluding a single (presumably gravid) female that moved 1830 feet in 53 days.

Although published information on _T. ornata_ is scant, a considerable amount of information is available concerning its congener, _T.

carolina_. The cla.s.sic studies of Stickel (1950) on it const.i.tute the most complete account of populations and movements for any reptile or amphibian, and probably, for any vertebrate. She found the average home range of adults to be 350 feet in diameter. Home ranges were not defended as territories and nearly all individuals were socially tolerant of one another. Movements (studied by means of a thread-trailing device) were characterized by frequent travel over the same routes within the home range. Some turtles concentrated their activities in only one part of the home range, moving subsequently to another part, and some turtles had two ranges between which they traveled at varying intervals. Females ordinarily left their home ranges to nest.

Other noteworthy, but less detailed, studies of populations of _T.

Carolina_ are those of Breder (1927) who found evidence of home range and homing behavior, and of Nichols (1939b) who, after observing a marked population on Long Island over a period of twenty years, found evidence of homing behavior and estimated normal home range to be approximately 250 yards in diameter. Numerous shorter papers such as those of Schneck (1886) and Medsger (1919) doc.u.ment the tendency of _T. carolina_ to remain in restricted areas over long periods.

Important studies that indicate the presence of home range and homing behavior in other chelonians are those of Cagle (1944) on _Pseudemys scripta_ and _Chrysemys picta_, and of Woodbury and Hardy (1948) on _Gopherus aga.s.sizi_. Grant (1936) and Bogert (1937) have also indicated that movements of individuals of _Gopherus aga.s.sizi_ are restricted to limited areas.

Locomotion

Ornate box turtles moving forward over even terrain hold the plastron a quarter to a half inch above the ground and keep the head and neck lowered and extended. Each foreleg is brought forward and the humerus points nearly straight ahead when the foot touches the ground. Nearly all of the palmar surface is initially in contact with the ground but as the body is brought forward and the humerus swings outward, only the claws, and finally, only the two inner claws are in contact with the ground. Of the hind feet, the medial surfaces are the princ.i.p.al parts that touch the ground but some traction is derived from the hind claws at the beginning of each cycle of the hind leg. Under normal conditions, box turtles move slowly and pause to rest and examine their surroundings every few feet. When resting, the plastron is in contact with the ground, the legs relaxed, and the head and neck are extended upward. Some turtles seeking shelter from the heat of suns.h.i.+ne walk rapidly for a hundred feet or more without pausing.

Turtles seen feeding under natural conditions displayed remarkable agility in making lunges, consisting of one or two short steps and a thrust of the head, at moving objects. Turtles kept in my home were able, after being conditioned to hand-feeding, quickly to intercept a grape rolled slowly across a linoleum-covered floor.

Frederick R. Gehlbach told me that, of several species of captive turtles observed by him, _T. ornata_ characteristically walked with the plastron held well above the substrate, as did _Gopherus berlandieri_, but that _T. carolina_ (specimens from the northeastern U. S.) dragged their sh.e.l.ls as they walked. Apparently _T. carolina_ in Kansas (currently referred to the subspecies _triunguis_) differs somewhat in gait from populations in the eastern part of the range; several individuals of _T. carolina_ from Kansas that I observed in captivity, kept their plastra raised well above the smooth, hard substrate over which they walked.

Box turtles at the Damm Farm were able easily to climb ravine banks that sloped at an angle of 45 degrees and, with some difficulty, could climb banks as steep as 65 degrees. Most individuals, however, were reluctant to walk directly downward on banks as steep as 45 degrees.

Several individuals were seen to lose footing when climbing up or down a steep bank and to roll or slide to the bottom. Ordinarily, _T.

ornata_ is able to climb over a sheer surface as high as its sh.e.l.l is long, provided the surface is rough enough to give some traction to the foreclaws. The claws of first one, then the other forefoot are placed over the top of the barrier and then a hind foot, extended as far forward as possible, secures a hold as the turtle goes over the barrier.

A number of observations on speed were made in the field where distance traveled and time elapsed were known approximately. Speeds ranged from 20 to 100 feet per hour in the course of foraging. Higher speeds (400 or more feet in one hour) were for turtles moving along pathways or seeking shelter. Gould (1957:346) observed somewhat faster speeds in _T. carolina_ (192 feet per hour in cloudy weather and 348 feet per hour in sunny weather); he observed individuals that had been removed from their normal home ranges.

Individuals of _T. ornata_ that were placed in water swam moderately well but were clumsy in comparison to individuals of more aquatic emyids such as _Pseudemys_ and _Chrysemys_. Box turtles were never observed to swim voluntarily, although they were frequently found in shallow water. On several occasions I confronted individuals at the edge of a pond so that the only unblocked route for their escape was through deeper water; nearly always these individuals attempted to crawl past me, to crawl away in shallow water parallel to the sh.o.r.e, or to hide in soft mud at the edge of the water. Box turtles floated high in the water with the dorsal side upward and had little difficulty in righting themselves when turned over. The head and neck are extended and submerged when the turtle is swimming; forward progress is interrupted every few moments to elevate the head, presumably for purposes of breathing and orientation. The sh.e.l.l is never submerged. The swimming of _T. ornata_ is in general like that of _Pseudemys_ or _Chrysemys_ that have become dehydrated after long periods out of water and cannot submerge. These more aquatic turtles, however, quickly overcome their bouyancy, whereas examples of _T.

ornata_, even if left in water for several days, are unable to submerge. Clarke (1950) saw an ornate box turtle swim a 60-foot-wide stream in Osage County, Kansas; his description of swimming agrees with that given above.

The meager swimming ability of _T. ornata_ is of apparent survival value under unusual conditions and enables _T. ornata_ to traverse bodies of water that would act as geographic barriers to completely terrestrial reptiles; however, swimming is a mode of locomotion seldom used under ordinary circ.u.mstances.

Gehlbach (1956:366) and Norris and Zweifel (1950:2) observed individuals of _T. o. luteola_ swimming in temporary rain pools and small ponds in New Mexico; the two authors last named saw an individual quickly enter a pond and dive beneath the water after being startled on the bank. Several of my colleagues, in conversation, have also reported seeing _T. o. luteola_ in small bodies of water in the southwestern United States.

Daily Cycle of Activity

The daily cycle of _T. ornata_ consists basically of periods of basking, foraging, and rest that vary in length depending upon environmental conditions. Turtles emerge from burrows, forms, and other places of concealment soon after dawn and ordinarily bask for at least a few minutes before beginning to forage; foraging is combined sometimes with basking, especially in open areas that are suitable for both kinds of activity. Foraging usually continues until shelter is sought sometime between mid-morning and noon. Turtles remain under cover (or continue to forage in shaded areas) until mid-afternoon or late afternoon when they again become active. They forage in both morning and afternoon. Study of travel records of a few of the turtles equipped with trailers suggests that, under normal conditions, activity is slightly greater in forenoon than in afternoon, but that the converse is true of gravid females seeking nesting sites. Strecker (1908:79) reported that captive _T. ornata_, after developing a feeding reflex, ate and retired until feeding time next day.

As environmental temperatures rise in summer, the period of mid-day quiescence is lengthened. In the hottest part of the year, some turtles remain under cover for several days at a time. In periods of clear, cool weather at the beginning and end of the growing season, some turtles remain abroad and bask for most of the day.

Examination of thread trails showed that activity of all individuals except nesting females was terminated at dusk. Breder (1927:236), Allard (1935:336), and Stickel (1950:358) reported a corresponding lack of nocturnal activity in _T. carolina_. _Terrapene o. ornata_ in Kansas, and _T. o. luteola_ in New Mexico (Norris and Zweifel, 1950:2)--unlike desert tortoises, _Gopherus aga.s.sizi_, which are active at night in hot weather (Woodbury and Hardy, 1948:186)--do not utilize the hours of darkness for foraging, even in the hottest part of the year.

Seasonal Cycle of Activity

Data obtained by mapping the movements of turtles that were equipped with trailing devices made it possible to compare distances traveled in the course of daily activities at different times of the year. Some of these data are expressed graphically in Figure 27. It should be noted that movement at all times in the season of activity was uneven; that is to say, an individual would move several hundred feet each day for a period of several days, and then, for an interval of one to several days, move only a few feet from one shelter to another, or not move at all. Such periods of rest could not be correlated definitely with environmental conditions; some individuals were inactive on days that were probably ideal (in terms of moderately warm temperatures and high humidity) for activity of box turtles. a.n.a.lagous rest periods were noted in _T. carolina_ by Stickel (1950:358).

Two males of _T. ornata_ that had been removed by me from their normal home ranges traveled the longest average distance per day (429 feet).

Gravid females in June traveled the next longest average distance per day (363 feet). The average distances traveled per day by non-gravid females in June (226 feet) and July (260 feet) and by males (within their known home ranges) in June (289 feet) were thought to approximate normal amount of movement under average environmental conditions. Average distance traveled per day by females in October (152 feet) was shortest because of frequent and extended rest periods.

Nevertheless, in October actual distances traveled on days of activity tended to be longer than in any other month. A gravid female traveled farther in a single day than any other individual of _T. ornata_ observed; she moved along a rock fence for approximately 700 feet, then left the study area and moved, in a nearly straight line, 1,200 feet across a cultivated field. Then the thread on her trailer was expended. The total distance moved, therefore, was at least 1,900 feet and probably more.

[Ill.u.s.tration: FIG. 27. Average distances traveled per day by males and females at different times of the year, determined by mapping of thread trails at the Damm Farm. The diagram for "homing males" represents the distances traveled by two males removed from their normal home ranges to test homing ability.

The data presented are for an aggregate of 136 days of trailing. Vertical and horizontal lines represent, respectively, the range and mean. Open and solid rectangles represent one standard deviation and two standard errors of the mean, respectively.]

An adult male at the Reservation traveled 2,240 feet in the 36-day period from October 16 to November 20, 1954, mostly on a wooded hillside. Eleven forms found along the route of the turtle's travels indicated that movement took place on roughly one out of three days in the elapsed period and demonstrated the sporadic nature of movements in autumn. The turtle remained active for an undetermined time after November 20.

Home Range

Data obtained from trailing and various methods of recapture at the Damm Farm indicated that each individual used only a small part of the total study area in the course of daily activities and tended to remain within a restricted area for a long time.

The number of recaptures of no individual was great enough to permit application of refined calculations of size of home range as described by Odum and Kuenzler (1955). For individuals that were recaptured six or more times, or individuals for which adequate trailing records were available, the area enclosed by a line joining the peripheral points of capture was considered adequately representative of the home range of that individual, unless recaptures were all within a few feet of each other or lay in an approximately straight line. If less than six records of recapture were available, home range was estimated, in the manner described by Fitch (1958:73), by averaging the distance between successive points of recapture and letting this average represent the radius of home range; the actual area of home range was determined by the formula, [pi](R), for the area of a circle.

Size of home ranges of males and females did not differ significantly and data for the two s.e.xes were combined in the final a.n.a.lysis. The average radius of the home ranges of 44 adults (captured a total of 146 times) was 278 feet (extremes, 71 to 913) when computed by measuring the distance between successive captures; the average area of these home ranges was 5.6 acres. Data from 10 turtles that had been recaptured only once were combined with data from 34 turtles that had been recaptured more than once when it was found that the average size of home range in these two groups did not differ significantly. Data concerning the home ranges of eight of the 44 individuals were sufficient to permit actual measurement of home ranges with a planimeter; home ranges of these eight individuals had an average area of five acres (extremes, 1.2 to 10.2).

A minimum home range could theoretically consist of the smallest area in which adequate food and shelter were available. Under favorable conditions a turtle could stay in an area ten to twenty feet in diameter. Although several such favorable small areas existed on the Damm Farm, box turtles seldom stayed in one for more than a day or two. Seemingly, therefore, factors additional to food and shelter influence size of home range. At the Damm Farm these additional factors seemed to be: rock fences that acted as physical barriers; areas that were cultivated, barren, or otherwise unfavorable, acting as ecological barriers; and, cowpaths and ravines that offered relatively un.o.bstructed routes along which box turtles tended to move.

One subdivision of the main pasture, the northwest corner area, is an example of a relatively small natural area in which many individual box turtles had home ranges. This tract of 28 acres was roughly triangular and was bordered on two sides by rock fences that contained no gates or other pa.s.sageways. On its third (southeastern) side the area sloped into a deep ravine. Habitat in this subdivision of the pasture (as well as in the other two subdivisions) was especially favorable for box turtles because of permanent water, rocky slopes, ravines, and several fruit trees. Box turtles usually foraged near the rock fences and the ravine (where dung was more abundant than in other parts of the area), and tended, as they foraged, to move parallel to these barriers. Turtles crossing the area eventually came either to one of the fences or the ravine. Therefore, most of the turtles in the northwest corner area eventually completed a circuit of the area.

Turtles that came to the ravine tended to move along its bottom or sides. Several turtles were known to cross the ravine and to forage in the gra.s.sy area on its southeastern side. These turtles usually re-entered the ravine by way of smaller side-ravines. Of 22 box turtles known to have home ranges in the northwest corner area, only two individuals (both gravid females) were known to leave the area in the period in which observations were made.

Two other subdivisions of the main pasture--the house pond area and the southern ravine area--although not so distinct as the northwest corner area in terms of limiting barriers, nevertheless const.i.tuted separate areas of favorable habitat, each of which contained a number of individual home ranges. Although the two areas were not far apart, but little movement was observed of turtles from one area to the other. The home range of only one turtle, an adult female, was known to include parts of both areas.

Unbroken expanses of tall gra.s.s seem not to be optimum habitat. The crest of the hill at the Damm Farm (Pl. 17, Fig. 1) was an area of more or less h.o.m.ogeneous gra.s.sy habitat. Turtles were seldom found on the crest of the hill although this area was as thoroughly searched for turtles as any other area. Known home ranges of nearly every individual observed were on either one of the sides of the hill but not on both sides.

At several places on the border of the pasture, turtles were able to move freely into cultivated areas but seldom did so except for nesting. Trailing records show that most of the turtles that entered one of the cultivated areas returned again to the pasture.

Ornate box turtles seem to find places of shelter by trial and error along regularly used routes of travel in their home ranges. The individuals that I studied never returned to the same forms, and seldom returned to the same natural burrows and dens. Probably foraging, basking, and watering sites are found also by trial and error.

Stickel (1950:375) placed considerable importance on the occurrence of transient turtles in populations of _T. carolina_; in estimating population density, she added to her study area a peripheral strip, half as wide as the average, estimated home range, to account for turtles that had home ranges only partly within the study area. The study area used by Stickel had no natural boundaries, as habitat conditions on all sides were essentially the same as those of the study area itself. The pasture at the Damm Farm, on the contrary, is a relatively isolated area of natural gra.s.sland, bordered by rock fences and cultivated fields. I believe that most of the box turtles found on the pasture were permanent residents there. Individual box turtles at the Damm Farm seemingly occupied but one home range and it did not change from year to year. Populations of _T. ornata_ in areas less isolated than the Damm Farm, like the populations of _T.

carolina_ studied by Stickel (_loc. cit._), could be expected to have a higher percentage of transient individuals and individuals with multiple or changing home ranges. Henry S. Fitch told me that he considered most of the individuals of _T. ornata_ that were captured only once at the Reservation were transients.

Several females at the Damm Farm traveled long distances from their home ranges to nest but other females nested within their known or estimated home ranges. Seemingly a complex of environmental factors, including soil texture, weather, availability of water, and possibly the urge for random wandering in the breeding season, governs the distances traveled by gravid females and the ultimate selection of a satisfactory nesting site. Females, because of their more extensive travels in the nesting season, seem more likely than males to have multiple or changing home ranges. Males of _T. ornata_ did not noticeably alter the extent or pattern of their movements in the breeding season. Hibernacula, unlike nesting sites, were within the known or estimated home ranges of all individuals studied.

[Ill.u.s.tration: FIG. 28. The movements of an adult (non-gravid) female of _T. o. ornata_ in the house pond area at the Damm Farm during a period of 24 days in July, 1955 (solid line), and a period of three days (broken line) in July, 1956. Solid dots represent the points where the turtle was found as her thread trail was mapped; hollow symbols represent points of recapture when no trailing thread was attached to the turtle.]

The actual home range of almost every individual studied, even of those individuals for which the most data were available, probably differed at least slightly from the observed or estimated home range. One adult female, for example, was captured six times in two years within a radius of approximately 50 feet. Another female was found 2780 feet from her last point of capture. These last two records were regarded as unusual; when they were grouped with records of the 44 individuals mentioned above, the average radius of home range for the entire group was much larger (327 feet).

[Ill.u.s.tration: FIG. 29. The movements of a gravid female of _T. o. ornata_ in the southern ravine area at the Damm Farm in a period of ten days in June, 1956. Her movements were, for the most part, in and around several ravines (shown on map by broken lines) where she was searching for a nesting site. For explanation of symbols see legend for Fig. 28.]

Homing Behavior