Notes on territorial and vocal behaviour of neotropical frogs of the genus Centrolenella

Male-male interactions of two species of centrolenid frogs (Centrolenella viridissima in Mexico; C. valerioi in Costa Rica) are described. This variously involves an approach sequence consisting of jerky rocking motions, an amplexus-like clasp, and a call. This call is different from the previously-described mating call, being of lower intensity and of slightly longer duration. It is suggested that it be termed an encounter call. THE tiny, green frogs of the family Centrolenidae represent a small but morphologically distinct assemblage of about 60 species ranging from Mexico to Paraguay and southeastern Brazil. These frogs are arboreal and breed along permanent, fastflowing streams from sea level to about 1800 m elevation. Little has been published concerning their life history, with the exception of the northernmost species, Centrolenella viridissima. Duellman and Tulecke (1960) reported on the breeding activity, mating calls, oviposition sites and tadpoles of this species in Mexico. Our paper presents data on territorial behavior and the existence of a call in males of two species of Centrolenella that apparently is distinct from their mating call. All times are expressed as Standard in World Time Zone 6 (in the United States, Central Time Zone). Observations were made by Adler on a population of C. viridissima along a rushing mountain stream in a deep, steep-sided gorge 3.1 km (by road) north of Teocelo (_ Teocello), Veracruz, Mexico, at an elevation of 1000 m. The sides of the gorge are densely covered with broadleaf trees, shrubs, and occasional bromeliad-encrusted oaks; much of this vegetation directly overhangs the water. Males were calling from vegetation above the water from 1900 to 2300 hours on 19 July 1964, when all of these observations were made. As reported by Duellman and Tulecke (1960), the call of this species is a single, short, and very high-pitched "peep"; in the present observations, the estimated duration of each call is less than one second, with the interval between calls typically 8 to 12 s (average, 10). One apparently territorial encounter was observed. A male (A) was seen at 2130 hours calling from the top of a large horizontal leaf 10 m above the water. As soon as a second male (B, sex determined by dissection) jumped onto the same leaf about 15 cm from A, the behavior of A changed noticeably. He began a jerky series of fore-and-aft rocking motions as he moved slowly and at constant speed towards B; A did not jump but walked in a seemingly deliberate fashion. As he did, his call changed to a medium-to-low pitched "preep" which was somewhat longer (1 s or slightly more in duration) and softer than the presumed mating call; additionally, the pitch of each call seemed to increase slightly with time. Because of the noisy stream below, it was difficult to hear the softer of the two calls. Thus, two field companions were asked to verify the existence, characteristics and source of the softer call, which they did accurately and without prior description. These softer calls were repeated at intervals of about 3 to 5 s. After the resident male (A) moved towards B, B also made a few jerky movements similar to those of A but always moved perpendicular to the axis of A's movements. When A finally contacted B he mounted from the left rear side and briefly effected an axillary-like amplexus before B quickly twisted from his grip. Male A did not pursue but reverted to the original loud "peep" calls. Male B then moved to a HERPETOLOGICA 30:75-78. March, 1974 This content downloaded from 157.55. 39.147 on Sun, 07 Aug 2016 06:51:24 UTC All use subject to http://about.jstor. org/terms 76 HERPETOLOGICA [Vol. 30, No. 1 nearby vine; A continued calling as he moved about on the top surface and underside of the leaf. Whenever B subsequently hopped back onto the leaf, A would resume the jerky movements and the softer "preep" calls; this sequence occurred three times before B finally left. Male B never called throughout these observations; male A, however, called continuously until 2300 hours when these observations were discontinued and individual B was collected. Successful oviposition was not observed but a clutch of 22 eggs in early cleavage was found the next morning attached to the underside of this leaf. Two other clutches were taken about 10-15 m from the first clutch; these were in early blastula and numbered 20 and 26 eggs, respectively. All frogs collected are deposited in the University of Michigan Museum of Zoology (number 125753). Similar observations were made by McDiarmid on Centrolenella valerioi in Costa Rica in 1971. A small stream emptying into the Quebrada Aguabuena in Tropical Wet Forest near the Tropical Science Center Research Station (elevation 15 m) near Rincon de Osa, Puntarenas Province, Costa Rica, was selected for a detailed study of the reproductive ecology and behavior of sympatric species of Centrolenella. The stream was 2-5 m in width and not more than 0.5 m deep during the study. It was completely covered by the forest canopy with many broad-leaved plants overhanging the water. The study site was visited from 1-3 times during each 24-hour period from 4-17 May. The call sites of males of several species were marked and their reproductive behavior recorded. At 1930 during the evening census of 14 May, a male C. valerioi (No. 1 in the study) was calling from its site on the ventral surface of a large leaf of Gustavia sp. (Lecythidaceae) 160 cm above and 40 cm in (shoreward) from the stream edge. This male had been located and followed continuously from 7 May. At 0420 on the following day, 15 May, this male was observed in amplexus with another male of C. valerioi. During the 4 or 5 minutes of observation, amplexus was broken and reinitiated several times. During amplexus one of the males (presumably the resident male) uttered several soft "squeaky" calls that were noticeably quieter and different from the typical mating call. It was not realized until later that the second frog was probably a male, since no eggs were visible through the transparent sides of the body and no new egg clutches were deposited in the area that night; as the specimen was not collected, we cannot rule out the possibility that it was a spent female. The resident male (No. 1) was in place that night and continued to call until 18 May when the study was terminated. A similar situation was recorded for another resident male of C. valerioi (No. 23). This individual was first located on 8 May calling from the underside of a leaf of Dieffenbachia sp. (Araceae) 140 cm above the water. It was monitored continuously and its call recorded on two occasions during the study. On 17 May, male 23 was calling at its site at about 0430. At 0447 two male C. valerioi were found on the leaf used by male 23; it was light enough to write without using a flashlight. One male, assumed to be the resident, was calling in the same place that male 23 had occupied previously. The other male, assumed to be an intruder, was giving the same soft calls that were noted in the first case described above. However, no amplexus was observed. At 0502 the nonresident male moved to the next leaf upstream and then disappeared into the vegetation. Male 23 continued to call until 0516, when all vocal activity along the stream ceased. By this time it was very light in the forest. Male 23 was calling again at the site at 2200 on 17 May. The other male was not seen