The color pattern changes in the course of development, and the shade of color changes in response to environmental conditions. At the time of metamorphosis, young are dark brown with specks of black and with a dark, cuneate, leaflike middorsal mark. The narrow end of this mark arises just behind the head, and the mark extends posteriorly as far as the hind leg insertions. At its widest, the mark covers about half the width of the dorsal surface. The lateral edges of the mark are sharply defined, but at its anterior and posterior ends it blends into the ground color. In most individuals smaller than 20 mm., this dorsal mark is well defined and conspicuous. As growth proceeds, however, it becomes faint. In frogs 19 to 25 mm. long the marks have disappeared. In individuals of this size the brown ground color is markedly paler than in those newly metamorphosed, but is darker than in adults.
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.