In preservative, head and dorsum dark brown with triangular spot between eyes; dark spots on head and scapular region and dark brown blotch posteriorly on dorsum; flanks creamy white with brown spots; groin creamy white mottled with dark brown; thighs brown above with dark brown transverse bars on anterior and posterior surfaces; inner surfaces of shanks and outer surfaces of tarsi barred with pale brown; dorsal surface of foot mottled brown and creamy white; ventral surface of foot and toes pale brown; forelimbs faintly barred with pale brown; belly white with a few pale brown spots; vocal sac flecked with pale brown; lower jaw marked with small white spots on lips.
Variation.—Geographic variation is evident in the snout-vent length, tibia length, and foot length, all in relation to snout-vent length, and the relative size of the tympanum to the eye (Table 1). The largest specimens are from the humid Pacific lowlands of Costa Rica; individuals from the Caribbean lowlands of Costa Rica, Canal Zone, and South America are smaller. A general trend for increase in size extends from South America to the Pacific lowlands of Costa Rica.
Most variation in color does not seem to be correlated with geography; color variation is nearly as great within a given population as between separated populations. However, most specimens from Rincón de Osa, Puntarenas Province, Costa Rica, are dusky brown, but a few are darker. In comparison with specimens from the Caribbean lowlands of Central America, specimens from the Pacific slopes in Costa Rica have a darker interorbital triangle. In some specimens from the latter area rugosities are present on the borders of the interorbital triangle, on the snout, on the upper eyelid, and on the heel. Specimens from the Caribbean lowlands are less tuberculate, and most individuals from there lack rugosities on the tarsus. Living individuals from Puerto Viejo, Heredia Province, Costa Rica, and from the Canal Zone, Panamá, are brown above with a metallic green tint. Rugosities are present on the posterior edges of the forelimbs in some specimens from throughout the range. In most respects, specimens from the Canal Zone resemble those from the Caribbean lowlands of Costa Rica more than they resemble those from the Pacific lowlands of Costa Rica, but some individuals from the Canal Zone are less metallic above and have small white spots dorsally on the body, head, and limbs.
A moderate amount of color change from night to day has been noted. At night, a male from Puerto Viejo, Heredia Province, Costa Rica, was grayish tan above with slightly darker markings; the flanks were pale yellowish green. By day, the dorsum was brown with darker markings, and the throat was pale gray with white flecks; the rest of the venter was creamy white. The groin was pale green with black mottling; the anterior and posterior surfaces of the thighs and inner edges of the tarsi were greenish yellow with black bars.
Table 1.—Geographic Variation in Size and Proportions in Males of Hyla boulengeri.
(Means in parentheses below observed ranges.)
| Locality | N |
Snout-vent length (mm.) |
Tibia length/ snout-vent |
Tympanum/ eye |
Foot length/ snout-vent |
| Costa Rica: Tilarán | 23 |
37.4-48.7 (43.8) |
0.52-0.58 (0.55) |
0.62-0.76 (0.71) |
0.39-0.45 (0.42) |
| Costa Rica: Rincón de Osa | 10 |
41.4-46.1 (44.0) |
0.54-0.60 (0.57) |
0.68-0.80 (0.74) |
0.40-0.45 (0.43) |
| Costa Rica: Alajuela Province | 13 |
35.6-43.1 (39.8) |
0.55-0.60 (0.57) |
0.63-0.78 (0.69) |
0.41-0.46 (0.44) |
| Costa Rica: Puerto Viejo | 25 |
37.5-42.9 (41.6) |
0.51-0.62 (0.55) |
0.63-0.79 (0.71) |
0.38-0.46 (0.43) |
| Costa Rica: Suretka | 9 |
38.7-42.0 (41.0) |
0.56-0.58 (0.56) |
0.53-0.72 (0.62) |
0.35-0.45 (0.42) |
| Panamá: Canal Zone | 16 |
36.7-42.9 (39.0) |
0.52-0.58 (0.54) |
0.70-0.78 (0.74) |
0.40-0.44 (0.42) |
| Venezuela: Santomé | 4 |
35.5-40.9 (38.5) |
0.45-0.48 (0.46) |
0.63-0.67 (0.65) |
0.36-0.40 (0.38) |
Table 2.—Comparison of Mating Calls in the Hyla rubra Group.
(Means in parentheses below observed ranges.)
| Species | N | Notes per call group | Duration of note (sec.) | Pulses per second | Fundamental frequency (cps) | Major frequencies (cps) | |
| Lower | Upper | ||||||
| H. boulengeri | 8 | 1 | 0.24-0.47 (0.35) | 80-120 (101) | 70-74 (71) | 1400-1820 (1611) | 2520-3182 (2840) |
| H. foliamorta | 7 | 1 | 0.23-1.86 (0.69) | 50-60 (51) | 52-61 (56) | 912-1026 (918) | 2736-3477 (3055) |
| H. elaeochroa | 15 | 2-95 (19) | 0.12-0.24 (0.17) | 40-50 (42) | 48-65 (57) | 1254-1586 (1499) | 2562-3477 (2911) |
| H. s. staufferi | 18 | 2-77 (23) | 0.13-0.23 (0.18) | 100-130 (120) | 96-130 (106) | 1582-1872 (1743) | 1962-3744 (3056) |
| H. s. altae | 7 | 2-22 (11) | 0.14-0.18 (0.15) | 110-130 (120) | 104-117 (112) | 1853-2106 (2008) | 3379-4056 (3775) |
Cranial Osteology.—The skull of Hyla boulengeri is as long as it is wide, and is flat; the premaxillary is small and bears 13 to 17 teeth (mean for 6 specimens, 14.9). The alary processes of the premaxillaries are widely separated, concave posteriorly, and vertical. Ventrally, the premaxillary is connected to the prevomer by bony tissues. The maxillary is slender and bears 70 to 91 teeth (mean for 6 specimens 78.1). The pars facialis of the maxillary is laterally convex and about four times as high as the pars dentalis.
The nasal is large (its length about 40 per cent of total length of skull), and pointed anteriorly and posteriorly in dorsal view. The nasals are separated anteromedially by the cartilaginous septum nasi. One or two protuberances are present on the midlateral concavity of the nasal. Posteriorly, the nasal overlaps the sphenethmoid and articulates with the palatine. Dorsally the sphenethmoid is large, pentagonal, and completely ossified. The frontoparietal is elongate, smooth, and bears a small supraorbital process on the anterior edge of the orbit. A keyhole-shaped frontoparietal fontanelle is present; the fontanelle is narrow anteriorly and wide posteriorly.