Oaxaca: Donají (15); 43 km. N of Matías Romero (19); Río Sarabia (2); Sarabia (11); Tolosita. Veracruz: Acayucan (17); Alvarado (41); Aquilera (21); 8 km. SW of Coatzacoalcos (10); Cosoleacaque (26); 10 km. SE of Hueyapan; Naranja (3); Novillero.
This frog is abundant in the Gulf lowlands of the isthmus, where large breeding congregations were found in grassy ponds on the savannas and in openings in the forest. Most frequently males were calling from grasses and reeds in the ponds; many individuals were perched precariously on thin blades as high as one meter above the water. The call is a series of low squeaks.
Individuals found at night were pale yellow above with light brown lines arranged in an irregular pattern on the back, but often forming a cross or an X-shaped mark in the scapular region. There is a brown stripe from the nostril to the eye and thence to the groin. Anteriorly this stripe is bordered above by a thin white or cream-colored line. Numerous small brown flecks are scattered on the back and dorsal surface of the shank. In most specimens there are thin transverse brown bars on the shank. The thighs and undersides of the limbs are golden yellow; the belly and vocal sac are lemon yellow. The iris is yellowish brown. During the day individuals assume a pale reddish tan ground color with darker brown markings. Twenty-five adult males from Alvarado have an average snout-vent length of 24.1 mm.
Hyla picta Günther
Oaxaca: Donají (8); Sarabia (11); Tolosita (15); Ubero (6). Veracruz: 19 km. N of Acayucan (4); Alvarado (5); Aquilera; 8 km. SW of Coatzacoalcos; 10 km. SE of Hueyapan (7); Lerdo de Tejada; Tula (3).
Widespread in the forests, scrub, and savannas on the Gulf lowlands of the isthmus, these frogs were found breeding at numerous localities. Males call from grasses and bushes growing in and about ponds. The call is a high-pitched insect-like trill. At night these frogs are pale yellow above; they change to light grayish tan during the day. A dark stripe extends from the nostril to the eye and thence posteriorly to a point between the axilla and groin. Above this dark stripe is a broader white stripe. Scattered on the dorsum are brown flecks or spots; the shanks are marked with poorly-defined cross-bars. The thighs are deep yellow below and paler above with scattered dark flecks. The belly is white, and the vocal sac is yellow. The iris is golden. Twenty males have an average snout-vent length of 21.5 mm.; three females, 24.0 mm.
Hyla robertmertensi Taylor
Oaxaca: Tapanatepec (28); 7.5 km. NW of Tapanatepec (38); 7.2 km. WNW of Zanatepec (77).
This species was found in the isthmian region only on the Pacific lowlands at the southern base of the western part of the Sierra Madre de Chiapas. On July 13, 1956, many large choruses were discovered. The calling males were on reeds and thorn scrub in and at the edge of temporary ponds; the call is a cricket-like "creak-creack," quickly followed by a series of notes "creak-eek-eek-eek-eek."
At night the dorsal ground color is pale yellow; this changes to pinkish buff during the day. There is a grayish or brown dark stripe from the nostril to the eye; the stripe continues to the groin. This dark stripe is bordered above by a narrow white stripe. The belly is white, and the vocal sac is yellow. The iris is dull reddish brown. Twenty-five males have an average snout-vent length of 24.7 mm.