The frogs of the _Hyla microcephala_ group breed in shallow grassy
ponds. In some places they breed in permanent ponds, but usually
congregate around temporary pools, such as depressions in forests,
flooded fields, and roadside ditches. At the height of their breeding
season, usually in the early part of the rainy season, the
congregations are made up of large numbers of individuals. In April,
1961, and in June, 1966, the senior author noted nearly continuous
choruses of _H. m. microcephala_ in roadside ditches along the 75
kilometers of road between Villa Neily and Palmar Sur, Puntarenas
Province, Cost Rica; on June 20, 1966, at Puerto Viejo, Heredia
Province, Costa Rica, he estimated approximately 900 _Hyla phlebodes_
in one pond, and two nights later noticed that the number of
individuals had increased substantially. Other observations by the
first author on size of breeding congregations include nearly
continuous choruses of _H. m. underwoodi_ between Villahermosa and
Teapa, Tabasco, in July of 1958, an estimated 400 _Hyla robertmertensi_
in a road side ditch 7.2 kilometers west-northwest of Zanatepec,
Oaxaca, on July 13, 1956, and approximately 150 _Hyla sartori_ around
a rocky pool in a riverbed, 11.8 kilometers west-northwest of Tierra
Colorada, Guerrero, on June 28, 1958.
The length of the breeding season seemingly is more dependent on
climatic conditions in various parts of Middle America than on
behavioral differences in the various species. Thus, Fouquette (1960b)
found in the Canal Zone that _H. m. microcephala_ formed breeding
choruses from May through January, the entire rainy season in that
area. In the wetter coastal region of Puntarenas Province, Costa Rica,
the species breeds as early as mid-March, whereas in the drier region
encompassing Guanacaste Province, Costa Rica, and southwestern
Nicaragua breeding activity is initiated by the first heavy rains of
the season, usually in June.
_Hyla phlebodes_ inhabits regions having rainfall throughout the year.
Although large breeding congregations are most common in the early
parts of the rainy season, males probably call throughout the year. At
Puerto Viejo in Costa Rica the senior author has heard _Hyla phlebodes_
in February, April, June, July, and August. Charles W. Myers noted
calling males of this species in the area around Almirante, Bocas del
Toro Province, Panama, in September, October, and February. An
exception to the correlation between rainfall and breeding activity
was noted by the junior author in _Hyla phlebodes_ in the Canal Zone,
where he noticed a decrease in activity of that species in October and
November, when the rains are heaviest and most frequent. Furthermore,
independent observations made by both of us indicate that _H.
phlebodes_ does not reach peaks of activity during or immediately
after heavy rains, but instead builds up to peaks of activity two or
three days after a heavy rain. This is in contrast to the other
species, all of which characteristically inhabit drier environments
than does _H. phlebodes_. Peaks of breeding activity in the other
species occur immediately after, or even during, heavy rains.
The calling location of the males generally is on vegetation above,
or at the edge of, the water. _Hyla microcephala_ and _H. phlebodes_
call almost exclusively from grasses and sedges; _phlebodes_ usually
calls from taller and more dense grasses than does _microcephala_.
Except for some minor differences in calling location observed by
the junior author (Fouquette, 1960b) in the Canal Zone, the differences
in density and height of grasses utilized for calling-locations
probably is dependent primarily on the nature of the available
vegetation. Although bushes and broad-leafed herbs are usually present
at the breeding sites, males of these species seldom utilize them for
calling locations. Both _H. robertmertensi_ and _H. sartori_ have been
observed calling from grasses, herbs, bushes, and low trees. Calling
males of _robertmertensi_ have been found two meters above the ground
in small trees.
Daytime retreats in the breeding season sometimes are no more than
shaded clumps of vegetation adjacent to a pond or in clumps of grass
in a pond. Individuals of _H. m. underwoodi_ were found by day under
the outer sheaths of banana plants next to a water-filled ditch. Dry
season refuges are unknown.
Amplexus is axillary in all four species. Egg deposition has been
observed in _H. m. microcephala_, _m. underwoodi_, and _phlebodes_.
In all three the eggs are deposited in small masses that float near
the surface of the water and usually are at least partly attached to
emergent vegetation. Each clutch does not represent the entire egg
complement of the female.
Tadpoles are definitely known of only _H. m. microcephala_ and
_phlebodes_; these have been described in the preceding accounts of
the species. The tadpoles of these two species can be distinguished
readily (Pl. 15). The tadpole of _H. microcephala_ has a uniformly
white venter and nearly transparent tail, whereas in _H. phlebodes_
the venter is flecked anteriorly and the tail is mottled. In life, _H.
microcephala_ is easily recognized by the orange posterior half of
the tail, whereas the tail in _H. phlebodes_ is mottled tan and grayish
brown.