Part 4

In large adults the dorsal coloration is a uniform pale tan, paler on the average in females than in males. Temperature and moisture both affect the shade of coloration. In frogs that were partly desiccated, the color was unusually pale, with a distinctly greenish tint, and at high temperatures coloration tended to be relatively pale.

Hecht and Matalas (1946) have described and figured color patterns in various populations of Gastrophryne, demonstrating geographic trends and helping to clarify relationships. Their account indicates that the dark dorsal mark present in young of olivacea but not present in adults, is better developed and longer persisting in other forms. Specimens of carolinensis, presumably adult, are figured which have the dark middorsal area contrasting with paler color of the sides. The dark area is seen to consist of dots or blotches of black pigment which may be in contact producing more or less continuous black areas, or may be separate and distinct producing a spotted pattern. Pigmentation is usually most intense along the lateral edges of the dorsal leaflike mark; the central portion may be so much paler that the effect is that of a pair of dorsolateral stripes. This latter type of pattern is best developed in the population of Key West, Florida. Hecht and Matalas did not consider these insular frogs to be taxonomically distinct, because only 48 percent of specimens from the Florida keys had the "Key West" pattern, while 29 per cent resembled olivacea and 23 per cent resembled carolinensis. In the southwestern subspecies (or species) mazatlanensis, recorded from several localities in Sonora and from extreme southern Arizona, the dorsal pigmentation similarly tends to be concentrated in dorsolateral bands, but is much reduced or almost absent, and there is corresponding pigmentation dorsally across the middle of the thigh, across the middle of the shank, and on the foot. When the leg is folded, these three dark areas are brought in contact with each other and with the dorsolateral body mark, if it is present, to form a continuous dark area, in a characteristic "ruptive" pattern. Hecht and Matalas found similar leg bars, less well developed, in certain specimens of olivacea including one from Gage County, Nebraska, at the northern end of the known geographic range.

MOVEMENTS

Freiburg (op. cit.: 384) concluded that ant-eating frogs seem to have no individual home ranges, but wander in any direction where suitable habitat is present. However, from records covering a much longer span of time, it became increasingly evident that a frog ordinarily tends to stay within a small area, familiar to it and providing its habitat requirements.

Nevertheless, in all but a few instances the marked frogs recaptured were in new locations a greater or lesser distance from the site of original capture. The movements made by these frogs were of several distinct types:

1. Routine day to day movements from shelter to shelter within the area familiar to the animal, the "home range."

2. Shifts from one home range to another; such shifts may have been either long or short, and may have occurred abruptly or by gradual stages.

3. Travel by adults to or from a breeding pond. In most or all instances these adults were regularly established in permanent home ranges, and they often moved through areas unsuitable as habitat to reach the ponds.

4. Movements of dispersal in the young, recently metamorphosed and not yet settled in a regular home range.

Usually there was uncertainty as to which types of movements had been made by the recaptured individuals. Some may have made two or three different types of movements in the interval between captures.

On many occasions individuals were found beneath the same rock on two consecutive days, or occasionally on several successive days. Rarely, such continued occupancy of a niche lasted several weeks. In 1949, a frog was found under the same rock on June 4, 6, 26, 27, and July 1, 3 and 11. This was an immature female, presumably metamorphosed late in the summer of 1948. During the five weeks period covered by the records, it grew from 27 mm. to 34 mm. In 1952, another individual was found under its home rock on June 23 and 30, July 2 and 3, and August 14 and 20. In 1952 a juvenile was found under a rock on May 30, June 4, and June 17. These three individuals were exceptional in their continued occupancy of the same niches. Among the hundreds of others recorded, none was found more than twice in any one place.

Despite the fact that field work was concentrated on small areas which were worked intensively, only eight per cent of the frogs recorded were ever recaptured, and most of those were recaptured only once. Only 13 individuals yielded series of records, well spaced, in two or more different years. These few individuals recaptured frequently may not be typical of the entire population. The low incidence of recaptures indicates that relatively few of the frogs present on an area at any one time have been taken. Because of their secretive and subterranean habits most of the frogs are missed by a collector who searches by turning rocks, or trapping with pitfalls. Therefore, even though a marked frog may survive and remain within a radius of a few hundred feet of one point for months or even years, the chances of recapture are poor.

One female was caught first as a juvenile on June 8, 1950. On April 24, 1951, when first recaptured, she had grown to small adult size, and was only 18 feet from the original location. On July 30, 1951, however, she was recaptured 750 feet away. At a fourth capture on May 21, 1952, she had shifted 70 feet farther in the same direction. At the final capture on June 24, 1952, she was approximately 140 feet from both the third and fourth locations. The sequence of these records suggests that the frog had already settled in a home range at the time of her first capture in 1950, and that approximately a year later she shifted to a second home range, which was occupied for the following year, at least.

In several instances, after recaptures as far as 400 feet from the original location, frogs were again captured near an original location, suggesting that for some individuals, at least, home ranges may be as much as 400 feet in diameter.

Figure 8 shows that for movements of up to 400 feet, numbers of individuals gradually decrease with greater distance. For distances of more than 400 feet there are comparatively few records. Of the 59 individuals recaptured after one or more hibernations, only nine had moved more than 400 feet from the original location. Twenty-five were recaptured at distances of 75 feet or less. The mean distance for movement for all individuals recaptured was 72 feet. A typical home range, therefore, seems to average no more than 75 feet in radius. Of the 59 individuals recaptured after one or more hibernations, 47 were adults and probably many of these had made round-trip migrations to the breeding pond. This was not actually demonstrated for any one individual, but several were captured in each of three or four different years near the same location.

The trend of movements differed in the sexes. Males are more vagile. Of 21 adult males recaptured, none was less than 40 feet from its original location, whereas six of the 26 adult females were less than 40 feet away from the original point of capture. Of seven frogs that had wandered 700 feet or more, five were males.

FOOD HABITS

According to Smith (1934: 503) stomachs of many specimens, from widely scattered localities in Kansas, contained only large numbers of small ants. Tanner (1950: 47) described the situation of a frog found on the Reservation buried in loose soil beneath a flat rock, beside an ant burrow, where, presumably, the frog could snap up the passing ants without shifting its position. Anderson (op. cit.: 21) examined alimentary tracts of 203 specimens of carolinensis from Louisiana, representing a year round sample for several different habitats. He found a variety of small animals including ants, termites, beetles, springtails, bugs, ear-wigs, lepidopterans, spiders, mites, centipedes, and snails. Most of these prey animals were represented by few individuals, and ants were much more numerous than any of the other groups. Anderson concluded that ants, termites, and small beetles were the principal foods. He noted that some of the beetles were of groups commonly found in ant colonies. Tanner reported that in a large number of the frogs which he collected in Douglas, Riley, Pottawatomie, and Geary counties, Kansas, the digestive tracts and feces contained only ants. Wood (1948: 226) reported an individual of G. carolinensis in Tennessee found under a flat rock in the center of an ant nest.

Freiburg (op. cit.: 383) reported on the stomach contents of 52 ant-eating frogs collected near the Reservation. Ants constituted nearly all these stomach contents, though remains of a few small beetles were found. The ants eaten were of two kinds, Lasius interjectus and Crematogaster sp. The latter was by far the more numerous.

Although I made no further study of stomach contents, the myrmecophagous habits of Gastrophryne have come to my attention frequently in the course of routine field work. Individuals kept in confinement for a day or more almost invariably voided feces which consisted mainly or entirely of ant remains, chiefly the heads, as these are most resistant to digestion.

Often upon examining frogs I have found ants (Crematogaster sp.) or their severed heads, attached with mandibles embedded in the skin. To have been attacked by ants, the frogs must have been in or beside the ants' burrow systems. Frequently the frogs that were uncovered beneath rocks were adjacent to clusters of ants or to their nests or travelways, in a position strategically located to feed upon them, as described by Tanner. Often the feces of the frogs were found in pitfalls or under flat rocks. Although these feces were not analyzed, they seemed to consist mainly or entirely of ant remains.

The species of Crematogaster, which is the chief food of Gastrophryne in this region, is largely subterranean in habits, and is extremely abundant. Any flat rock in damp soil is likely to harbor a colony beneath it. Colonies are situated also in damp soil away from rocks, beneath almost any kind of debris, and in hollow weed stalks and decaying wood. Live-traps for small mammals, having nest boxes attached, almost always were occupied by colonies of Crematogaster, if they were left in the field in warm, humid weather. Occasionally the ants attacked and killed small mammals caught in such traps. Among the thousands of kinds of insects occurring on the Reservation, this ant is one of the most numerous in individuals, one of the most important on the basis of biomass and provides an abundant food source for those predators that are ant eaters. Food supply probably is not a limiting factor to populations of Gastrophryne on the area.

PREDATION

Young copperheads are known to feed upon ant-eating frogs occasionally (Anderson, 1942: 216; Freiburg, 1951: 378). Other kinds of snakes supposedly eat them also. The common water snake (Natrix sipedon) and garter snake (Thamnophis sirtalis) probably take heavy toll of the adults at the time they are concentrated at the breeding pools. Larger salientians may be among the more important enemies of the breeding adults, the tadpoles, and the newly metamorphosed young. Bullfrogs (Rana catesbeiana) and leopard frogs (Rana pipiens) are normally abundant at the pond on the Reservation. These large voracious frogs lining the banks are quick to lunge at any moving object, and must take heavy toll of the much smaller ant-eating frogs that have to pass through their ranks to reach the water. The newly metamorphosed young often are forced to remain at a pond's edge for many days, or even for weeks, by drought and they must be subject to especially heavy predation by ranid frogs. Even the smallest newly metamorphosed bullfrogs and leopard frogs would be large enough to catch and eat them.

As a result of persistent drought conditions in 1952 and 1953, bullfrogs were completely eliminated from the pond by early 1954. Re-invasion by a few individuals occurred in the course of the summer; these probably made long overland trips from ponds or streams that had persisted through the drought. Leopard frogs reached the pond in somewhat larger numbers, but their population in 1954 was only a small percentage of that present in most other years. Notable success in the ant-eating frog's reproduction in 1954 may have been due largely to the scarcity of these large ranids at the breeding ponds.

Freiburg (loc. cit.) noted that many of the ant-eating frogs he examined were scarred, and some had digits or limbs amputated. He did not speculate concerning the origin of these injuries. However, it seems likely that many or all of them were inflicted by the short-tailed shrew (Blarina brevicauda). Five-lined skinks living on the same area were likewise found to be scarred by bites which I identified (Fitch, 1954: 133) as bites of the short-tailed shrew. This shrew is common on the Reservation, especially in woodland. Many have been trapped in the pitfalls. On several occasions when a short-tailed shrew was caught in the same pitfall with ant-eating frogs, it was found to have killed and eaten them. Like the frogs, the shrews were most often caught in pitfalls just after heavy rains. Once in 1954 a shrew was found at the quarry in a pitfall that had been one of those most productive of frogs. The bottom of the pitfall was strewn with the discarded remains (mostly feet and skins) of perhaps a dozen ant-eating frogs. All had been eaten during one night and the following morning, as the trap had been checked on the preceding day. On other occasions shrews caught in pitfalls with several frogs had killed and eaten some and left others unharmed.

SUMMARY

In northeastern Kansas the ant-eating frog, Gastrophryne olivacea, is one of the more common species of amphibians. This area is near the northern limits of the species, genus, and family. The species prefers a dry, rocky upland habitat often in open woods or at woodland edge where other kinds of salientians do not ordinarily occur. It is, however, tolerant of a wide variety of habitat conditions, and may occur in river flood plains or cultivated land. In these situations where surface rocks are absent, cracks and rodent burrows presumably furnish the subterranean shelter that it requires.