An experimental study of acoustic interference between two species of neotropical treefrogs (original) (raw)
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Intra- and Interspecific Vocal Behavior of the Neotropical Treefrog Hyla microcephala
Copeia, 1985
The vocal communication of Hyla microcephala was studied in central Panama. We recorded natural interactions between males and conducted playback experiments using conspecific and heterospecific calls. Males employ both advertisement and aggressive calls which consist of a buzz-like introductory note often followed by secondary click notes. Advertisement calls show little variation in temporal features, whereas aggressive calls are quite variable. Playback of both conspecific advertisement calls and aggressive calls at high intensity elicited a significant increase in aggressive calling. Males increased the duration of aggressive call introductory notes in response to increasing playback intensity. Aggressive calls with long introductory notes were also used during close vocal or physical encounters with both conspecific males and H. ebraccata. In most cases, playback of heterospecific calls were ineffective in eliciting increased aggressive calling. Males synchronized and often added click notes to advertisement calls in response to conspecific and heterospecific calls. Call playbacks also elicited an increase in calling rate. When interrupted, males often abruptly terminated calls or added secondary notes to them. Males typically alternate individual notes in overlapping calls. Internote intervals in overlapping multi-note calls are longer than those in non-overlapping calls, reducing the probability of note overlap. ACOUSTICALLY signaling animals which call in dense choruses are faced with two major problems: 1) intense competition among males to attract mates, and 2) acoustic interference from the calls of both conspecific and heterospecific males which reduce an individual's ability to broadcast his calls effectively (Alexander, 1975; Greenfield and Shaw, 1983; Schwartz and Wells, 1983a, b, 1984a). Male frogs exhibit several adaptations which probably make their calls more conspicuous in a noisy chorus and thereby increase their chances of attracting mates. These include increasing the rate of calling, increasing the complexity of calls by adding notes to them, and shifting the timing of calls to avoid overlap with those of neighbors (Loftus
Vocal Communication In a Neotropical Treefrog, Hyla Ebraccata: Aggressive Calls
Behaviour, 1984
We studied the vocal communication of Hyla ebraceata in central Panama. The advertisement call of this species consists of a pulsed buzz-like primary note which may be given alone or followed by 1-4 secondary click notes. Primary notes are highly stereotyped, showing little variation within or among individuals in dominant frequency, duration, pulse repetition rate or rise time. Males calling in isolation give mostly single-note calls. They respond to playbacks of conspecific calls by increasing calling rates and the proportion of multi-note calls, and by giving synchronized calls 140-200 ms after the stimulus begins. Responses to conspecific advertisement calls are usually given immediately after the primary note of the leading call, but the primary note of the response often overlaps with the click notes of the leading call. Experiments with synthetic signals showed that males synchronize to any type of sound of the appropriate frequency (3 kHz), regardless of the fine structure of the stimulus. Playbacks of synthetic calls of variable duration showed that males do not synchronize well to calls less than 150 ms long, but they do to longer calls (200-600 ms). The variance in response latency increased with increasing stimulus duration, but modal response times remained at around 140-200 ms. Similar results were obtained in experiments with synthetic calls having a variable number of click notes. Males showed no tendency to increase the number of click notes in their calls in response to increasing stimulus duration or increasing number of clicks in the stimulus. Females preferred three-note to one-notecalls in two-choice playback experiments, whether these were presented in alternation, or with the one-note call leading and the three-note call following. Females showed no preference for leader or follower calls when both were one-note. When two-note calls were presented with the primary note of the follower overlapping the click note of the leader, females went to calls in which click notes were not obscured. Our results indicate that male H. ebraeeata respond to other males in a chorus in ways which enhance their ability to attract mates.
Journal of Herpetology, 2013
We evaluated the hypothesis that adjustments in call duration made by male Gray Treefrogs render their calls less easily masked in noise and so facilitate communication with females in choruses. We also tested whether shifts in male call duration and rate can be elicited through changes in the level of filtered background noise. We found that males increased the number of pulses in their calls while lowering call rate with elevations in noise level in a fashion similar to that reported during broadcasts of calls. In phonotaxis tests with females using unmodulated or modulated background noise and calls (10, 20, 30, or 40 pulses long) presented at either unequal or equal rates, we failed to find significant differences in noise levels at call recognition thresholds for calls of different duration. However, calls were detected more easily (i.e., noise levels at recognition thresholds were higher) when the noise background was modulated as compared to unmodulated. Our results and those of an earlier study by our laboratory indicate that changes in vocal behavior made by males of Hyla versicolor in response to changes in the calling of other males and background noise within choruses likely do not function to lessen the problems of signal detection or degradation due to interference. Accordingly, a small advantage accruing to males because of an inherent, albeit context-dependent, female preference for long calls (even at low call rates) may account for the dynamic calling behavior of male Gray Treefrogs.
Interspecific acoustic interactions of the neotropical treefrog Hyla ebraccata
Behavioral Ecology and Sociobiology, 1984
The three species have calls exhibiting broad frequency overlap and call during the same season and time of day from similar microhabitats, frequently in close proximity. The vocal repertoires of the three species are structurally and functionally similar. All employ multi-part advertisement and aggressive calls which consist of a primary note followed by a variable number of clicks. H. ebraccata males often responded to heterospecific calls with multi-note synchronized responses, and calls with primary notes greater than 150-200 ms were most effective in eliciting synchrony. Playback experiments with synthetic 1-note advertisement calls of different durations and both synthetic 1-note advertisement calls and 200 ms tones of different frequencies demonstrated that H. ebraccata males will synchronize with stimuli which are similar in frequency and duration to conspecific calls. Data from a two-choice experiment with female H. ebraccata demonstrate that calls of individual H. microeephala can reduce the attractiveness of a H. ebraccata male's calls if primary notes overlap. By synchronizing response calls to those of H. microcephala, a H. ebraccata may reduce the chances that his calls are rendered less attractive to potential mates. Aggressive calls of these species are graded and are characterized by higher pulse repetition rates and often longer durations than advertisement calls. H. ebraccata males respond to aggressive calls of H. microcephala and H. phlebodes as they do to their own calls. Heterospecific aggressive interactions probably occur because the species interfere acoustically. Our results demonstrate that H. ebraccata males behave in ways which enhance their ability to communicate in a noisy assemblage of conspecific and heterospecific males.
Vocal communication in a neotropical treefrog, Hyla ebraccata: Advertisement calls
Animal Behaviour, 1984
We studied the vocal communication of Hyla ebraceata in central Panama. The advertisement call of this species consists of a pulsed buzz-like primary note which may be given alone or followed by 1-4 secondary click notes. Primary notes are highly stereotyped, showing little variation within or among individuals in dominant frequency, duration, pulse repetition rate or rise time. Males calling in isolation give mostly single-note calls. They respond to playbacks of conspecific calls by increasing calling rates and the proportion of multi-note calls, and by giving synchronized calls 140-200 ms after the stimulus begins. Responses to conspecific advertisement calls are usually given immediately after the primary note of the leading call, but the primary note of the response often overlaps with the click notes of the leading call. Experiments with synthetic signals showed that males synchronize to any type of sound of the appropriate frequency (3 kHz), regardless of the fine structure of the stimulus. Playbacks of synthetic calls of variable duration showed that males do not synchronize well to calls less than 150 ms long, but they do to longer calls (200-600 ms). The variance in response latency increased with increasing stimulus duration, but modal response times remained at around 140-200 ms. Similar results were obtained in experiments with synthetic calls having a variable number of click notes. Males showed no tendency to increase the number of click notes in their calls in response to increasing stimulus duration or increasing number of clicks in the stimulus. Females preferred three-note to one-notecalls in two-choice playback experiments, whether these were presented in alternation, or with the one-note call leading and the three-note call following. Females showed no preference for leader or follower calls when both were one-note. When two-note calls were presented with the primary note of the follower overlapping the click note of the leader, females went to calls in which click notes were not obscured. Our results indicate that male H. ebraeeata respond to other males in a chorus in ways which enhance their ability to attract mates.
Calling in gray treefrog choruses: Modifications and mysteries
The Journal of the Acoustical Society of America, 2013
Frogs are well known model systems in the study of communication for investigating the influences of noise on both signaling behavior and auditory processing. The best-studied frogs in this regard are two sister-species in the Hyla versicolor species complex (H. versicolor and H. chrysoscelis). Males of both species produce loud, pulsatile advertisement calls that function to attract females. In the competitive social environment of a breeding chorus, males commonly shift to producing longer calls (with more pulses) at slower rates when the level of competition increases. These behavioral modifications can be evoked in controlled laboratory experiments using playbacks of calls and chorusshaped noise. In contrast to birds and mammals, however, there is no evidence that males increase the amplitude of their vocalizations (the Lombard Effect) in response to increasing noise levels. In addition, current evidence suggests that males do not necessarily profit significantly from producing longer calls at slower rates in terms of increasing their overall attractiveness to females, overcoming interference by overlapping calls, or increasing the detectability of their calls in noise. Despite the robust and directional nature of call modifications in noise, the evolutionary function of these modifications remains obscure.
Marathon callers: acoustic variation during sustained calling in treefrogs
2011
We investigated the effects of within-night sustained calling on call acoustic properties in a typical lek-breeding anuran (Hyla intermedia), in which males engage in intense acoustic competitions to attract females. We continuously recorded the calling of randomly selected males over a large portion of the nightly chorus activity and investigated the pattern of temporal variation in both fine-scale (pulse rate, call duration and rise-time) and gross-scale (call rate, call-group duration) properties.
Why stop calling? A study of unison bout singing in a Neotropical treefrog
Animal Behaviour, 1991
Chorusing males of the Neotropical treefrog, Hyla microcephala, call in distinct bouts punctuated by periods of silence, known as unison bout singing. Previous studies of the calling energetics of frogs do not support the idea that males periodically stop calling because of high muscle lactate levels. Three additional hypotheses of why calling periodically ceases were tested. A two-stimulus female choice experiment failed to support the hypothesis that females prefer males that call cyclically. Playback experiments with males in the field rejected the hypothesis that males stop calling because of high ambient noise. Rather, data indirectly supported the hypothesis that males cease calling to save energy. Male H. microcephala adjust the timing of notes in their multi-note calls when interrupted by notes of other males. The flexibility of note timing was tested by interrupting males with call-triggered computer-generated advertisement calls of 20-1000 ms. The vocal behaviour of the frogs reduced acoustic interference significantly for most stimulus durations and probably allows males to minimize note overlap with their closest neighbours in the chorus while continuing to call when chorus noise levels are high.
Ethology Ecology and Evolution
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