Description and Variation.—For the purposes of analyzing geographic variation in size and proportions, measurements were taken on ten adult males from each of five samples throughout the range of the species. Aside from the data summarized in Table 2, the average ratio of tibia length to snout-vent length is noticeably less in Colombian specimens (53.4 per cent, as compared with 54.8 to 57.8 per cent in the other samples) and the ratio of head length to snout-vent length is noticeably less in Costa Rican specimens (33.5 per cent as compared with 34.9 to 35.1 per cent in the other samples). Also, specimens from Heredia Province, Costa Rica, have a relatively smaller tympanum (62.7 to 80.4 [mean 68.4] per cent of the diameter of the eye, as compared with means of 74.0 to 77.9 per cent in the other samples).
Two populations are distinctive as regards the size of adult males. Specimens from the northern Caribbean lowlands of Nicaragua (Bonanza, the northernmost locality for the species) are remarkably small. Males having snout-vent lengths of between 40 and 43 mm. were breeding; the largest male found had a snout-vent length of 47.7 mm. The other extreme in size is attained in specimens from the Pacific lowlands of eastern Costa Rica and western Panamá, where most breeding males have snout-vent lengths of more than 55 mm.; the largest male had a snout-vent length of 64.9 mm.
The rather striking differences in size among certain samples and the minor differences in proportions among other samples show no geographic trends. Instead, the variations apparently are random among the samples. The data presented here possibly are the results of inadequate sampling, but more likely reflect actual differences in the populations.
The dorsal ground color of Smilisca phaeota is pale green to tan; the venter is creamy white. The dorsum is variously marked with dark olive-green or dark brown spots or blotches (Pl. 6C). A dark interorbital bar is usually present. Usually a large dark dorsal mark extends from the occiput to the sacral region, but in many individuals this blotch is replaced by two or three dark marks. The dorsal markings are irregular in shape and do not tend to form transverse bands or longitudinal bars. The hind limbs are marked by dark transverse bands, usually four or five on the thigh, five or six on the shank, and four on the tarsus. Two or three narrow bands are usually present on the proximal part of the fourth toe. The webbing on the feet is brown. The loreal region is pale green, bordered above by a narrow dark brown canthal stripe extending from the nostril to the orbit. The upper lip is silvery white. A broad dark brown or black mark extends posteriorly from the orbit, encompassing the tympanum, to a point above the insertion of the forelimb. The flanks are pale green or pale tan and marked with a fine dark brown or black venation. The anterior surfaces of the thighs usually are pale brown or grayish tan, sometimes having small, indistinct darker flecks. The posterior surfaces of the thighs are similarly colored, but in most specimens small but distinct dark flecks are present; in some specimens small cream-colored spots are also present on the posterior surfaces of the thighs. A distinct, narrow creamy white anal stripe usually is present. A distinct white stripe is present on the outer edge of the tarsus and fifth toe; on the tarsus the white stripe is bordered below by dark brown. A white stripe also is present on the outer edge of the forearm and fourth finger. In breeding males the throat is dark gray.
Little geographic variation in color or pattern is evident. Few, if any, specimens from the Pacific lowlands of South America are green in life. (We have seen no living individuals from South America.) Some living individuals from Costa Rica and all those seen alive from Nicaragua have a tint of pale blue on the flanks. In some specimens the dorsal pattern is so faint as to be barely discernible, whereas in most specimens the pattern is bold.
The coloration in the living frogs is highly variable due to extreme metachrosis. Individuals of this species are capable of changing the dorsal coloration from green to brown in a short period of time. Both green and brown individuals have been found active at night. Usually those individuals found hiding by day are brown. One individual from Finca La Sumbadora, Panamá (now KU 91914), was kept alive in the laboratory for nearly one month. This individual usually was pale green with tan dorsal markings at night and tan with pale green markings by day. On occasion the pale green dorsal markings were boldly outlined by bright dark green.
In living individuals from throughout the range of the species the iris is a bronze color, darkest medially with fine black reticulations.
Natural History.—Smilisca phaeota inhabits humid lowland tropical forest and seldom ascends the foothills to more than 1,000 meters. The rather equable climatic conditions, especially more or less evenly distributed rainfall throughout the year, permit this frog to be active most of the year. Dunn (1931:413) reported males calling on Barro Colorado Island, Panamá, in February and in July, and Breder (1946:416) noted calling individuals in the Chucanaque drainage of Darién, Panamá in January, March, July, August and October and in Costa Rica in April through August inclusively. Calling males were found at Bonanza, Nicaragua in March and in July.
At all times of year the usual daytime retreats for these frogs are near water; the frogs have been found in elephant ear plants (Xanthosoma) and in bromeliads; occasional individuals have been found sitting on shaded branches of bushes and trees. None has been observed on the ground or beneath ground-cover by day.
The length of the breeding season cannot be determined definitely. The earliest date on which eggs have been found is May 23; Gaige, Hartweg, and Stuart (1937:5) reported a gravid female taken at El Recreo, Nicaragua, in September, and we have a gravid female taken at Almirante, Panamá, in March.