Small Headed Treefrog

Dendropsophus microcephalus is a small frog. Adult males have a snout vent length of up to 27 mm (McCranie and Wilson 2002). Honduran females measure up to 29 mm (McCranie and Wilson 2002), while Mexican and Costa Rican females may reach 30.6 mm (Duellman 2001). The head is flat and the snout is round and short. Eyes have horizontally elliptical pupils. Nostrils are laterally directed and the area between nostrils is somewhat concave. No vertical rostral keel is present. The tympanum is located slightly below the eye at a distance of about its own length. The supratympanic fold is weak. The tongue is ovoid and free for about one-third of its length posteriorly. Maxillary teeth are conical. Vomerine teeth are present, with tooth patches on raised ridges between ovoid to elliptical choanae and separated by slightly less than their own length. The dorsal skin is generally smooth, while the ventral surfaces range from weakly granular on the throat to coarsely areolate on the belly. This species has a well-developed axillary membrane. The upper arm is slimmer than the forearm. A weak transverse dermal fold is present on the upper surface of the wrists but no vertical dermal fold is present on the elbow. A weakly defined inner tarsal fold is present, which spans the length of the tarsus, but no dermal ridge is present along the posterior ventrolateral edge of the tarsus. (McCranie and Wilson 2002). Fingers are 1/3 webbed and the toes 3/4 webbed (Duellman 2001). Lateral keels are present on unwebbed sections of the fingers. Fingers and toes have discs expanded to a nearly ovoid shape with rounded disc covers. The discs on the toes are slightly smaller than the discs on the fingers. Subarticular tubercles are present on the fingers and are globular to conical and round. Supernumerary tubercles are not present on the fingers. The palmar tubercle is low, ovoid, and sometimes bifid to occasionally indistinct. The accessory palmar tubercles are round and slightly raised. The prepollex is round, enlarged and does not bear nuptial excrescences. On the toes, the subarticular tubercles are spherical in shape. Supernumerary tubercles are not present on the toes. The inner metatarsal tubercle is oval and raised, and the outer metatarsal tubercle is small, rounded and elevated. There is no vertical dermal fold on the heel. No nuptial pads are present (McCranie and Wilson 2002). This species can undergo metachrosis, or color change. During the night, the dorsum is a light yellow color with various brown or tan markings. During the day, the dorsum is a tan-yellow color, or light brown with darker brown or red markings (Duellman 2001). The venter is white, and breeding males have a yellow vocal sac (Duellman 2001). This frog has uniformly yellow thighs with a brown line, often bordered with a narrow white line extending from the nostril to the vent (Leenders 2001). The dorsal pattern on this species is variable; many individuals have an "X" shape on their backs, or two longitudinal bars connected with a crossbar. Others have irregularly placed dark brown dashes. In specimens from Mexico and Guatemala, the lateral brown stripe only extends to the sacral region, but in Costa Rica, many specimens have a stripe that extends to the groin (Duellman 2001). The iris is bronze. (McCranie and Wilson 2002). Dendropsophus microcephalus tadpoles collected east of Esparta, Costa Rica typically had a total length of 28 mm and a body length of 9.2 mm (Duellman 2001). Eyes are dorsolateral and the snout is pointed. The body is wider than it is deep. The mouth has finely serrated beaks and no teeth. The dorsal fin reaches onto the body. The spiracle is sinistral. Tadpoles have a yellow dorsum and a white venter, and the posterior half of the tail is orange. A brown stripe runs from the larval snout through the eye (Campbell 1998).The diploid chromosome number is 30 (Duellman, 2001). A Spanish-language species account can be found at the website of Instituto Nacional de Biodiversidad (INBio) (http://darnis.inbio.ac.cr/FMPro?-DB=UBIpub.fp3&-lay=WebAll&-Format=/ubi/detail.html&-Op=bw&id=4197&-Find).

Dendropsophus microcephalus ranges from the Pacific lowlands in southeastern Costa Rica eastward to Colombia (subspecies Dendropsophus microcephalus microcephalus); from northern South America to the Amazon basin (subspecies D. m. misera), and from Mexico down to northwestern Costa Rica (subspecies D. m. underwoodi) (Duellman 2001; Bolaños et al. 2008; Bolívar-G et al. 2009). It is also found in Trinidad and Tobago (Duellman 2001; Bolaños et al. 2008). In Honduras, this frog is found almost all areas, including the Bay Islands, except for the extreme south and southwest (McCranie and Wilson 2002). The subspecies D. m. microcephalus occurs at elevations below 560 m, in Colombia (Duellman 2001). The subspecies D. m. underwoodi is not found at elevations higher than 350 m in Mexico and Guatemala, but is found at higher elevations in more southern regions. For instance, it has been collected at 780 m in Silencio, Costa Rica; at 830m in Montana de Guaimaca, Honduras; at 960 m in Finca Tepeyac, Nicaragua, and at 1200 m in Finca Renecia, Nicaragua (Duellman 2001). Dendropsophus microcephalus is mainly found in pastures or disturbed forests (Leenders 2002). It is not seen within primary rainforests but instead around their borders in open spaces, roadside trenches, and short-lived ponds (Savage 2002). In the Bay Islands of Honduras, this species lives around hardwood forests, swamps and marshes (McCranie et al. 2005).

During the mating season, the male frogs gather in large groups around the breeding areas and call from grasses or sedges at the edge of water, or while perched on emergent vegetation. Preferred breeding areas are temporary ponds, shallow ditches, or marshes. The eggs of this species are laid on or near the surface of the water, where they are usually attached to emergent vegetation (Duellman 2001).The distinct “creek-eek-eek-eek” insect-like calls are characterized by a primary unpaired note with a series of short, secondary paired notes (Duellman 2001). The repetition rate of the mating call is 197 to 384 notes per minute. The primary note duration is 0.05 to 0.15 s, and the secondary note has duration of 0.06 to 0.11 s. Males usually sing in large choruses, with thousands of individuals. However, during the dry season, only a few males may gather and call from a drying swamp (Campbell 1998). Instead of calling independently, males will respond to conspecific males and other male species within a group. In an experiment conducted by Schwartz and Wells (1985), males synchronized to individual calls and also responded to distant choruses. Some female species preferred males with more aggressive and repetitive calling, and D. microcephalus began calling more repetitively and rapidly when females were nearby (Schwartz and Wells 1985). Males will avoid note and call overlap because it impairs their ability to distinguish themselves to potential mates and prevents them from hearing and assessing their neighbor's calls (Schwartz 1987). Kaiser et al. (2011) found that anthropogenic noise decreases both the long- and short-term duration of individual male frog presence in the breeding chorus. Since females join the choruses later at night, the effect of increased exogenous noise is to decrease the time males and females overlap at the breeding pond.

This species appears to be both abundant and increasing, and occurs within a number of protected areas (Bolaños et al. 2008). It can tolerate disturbed habitat and has been found near roads and human settlements (Bolívar-G et al. 2009). However, a study by Kaiser et al. (2011) found that anthropogenic noise had the effect of decreasing the amount of time males spent in the breeding chorus, both short-term and long-term. This phenomenon may result in local declines.

Dendropsophus microcephalus is a species of frog in the family Hylidae. It is found in southeastern Mexico (southern Veracruz and northern Oaxaca), Central America (Belize, Costa Rica, El Salvador, Guatemala, Bangladesh, Honduras, Nicaragua, Panama), and northern South America in Colombia, Venezuela, Trinidad and Tobago, the Guianas (Guyana, Suriname, French Guiana ), and northern Brazil. This widespread species might actually be a species complex. Its common names include yellow treefrog, small-headed treefrog, and yellow cricket treefrog.