Playback Of Conspecific Calls Research Articles

Trialling camera traps to determine occupancy and breeding in burrowing seabirds

AbstractBurrowing seabirds are important in ecological and conservation terms. Many populations are in flux due to both negative and positive anthropogenic impacts, but their ecology makes measuring changes difficult. Reliably recording key metrics, the proportion of burrows with breeding pairs and the success of breeding attempts requires burrow‐level information on occupancy. We investigated the use of camera traps positioned at burrow entrances for determining the number of breeding pairs in a sample to inform population estimates, and for recording breeding success. The performance of two cameras makes we tested differed markedly, with Spypoint Force 10 trail cameras prone to malfunction while Reconyx HC600 Hyperfire cameras performed well. Nevertheless, both makes yielded season‐long activity patterns for individual burrows, eliminating uncertainty around successful fledging attempts. Dimensionality reduction of activity metrics derived from camera time series suggests breeding and non‐breeding burrows may be identifiable using linear discriminant analyses but sample sizes from our trial were low and group means were only significantly different during certain breeding stages (permutational multivariate analysis of variance: early chick‐rearing f = 3.64, P = 0.06; late chick‐rearing f = 8.28, P = 0.009). Compared with traditional techniques for determining burrow occupancy (e.g. manual burrow inspection and playback of conspecific calls at burrow entrances), camera traps can reduce uncertainty in estimated breeding success and potentially breeding status of burrows. Significant up‐front investment is required in terms of equipment and human resources but for long‐term studies, camera traps may deliver advantages, particularly when unanticipated novel observations and the potential for calibrating traditional methods with cameras are factored in.

Timing of the advertisement call of the common tink frog (Diasporus diastema) shifts with the acoustic behaviour of local conspecifics

ABSTRACTWe investigated the temporal dynamics of acoustically interacting common tink frogs (Diasporus diastema), a species in which advertising males maintain large inter-individual distances that may influence call timing behaviours among nearest neighbours. This species produces advertisement calls in temporally structured bouts, with decreasing inter-note intervals that culminate in a ‘burst’ sequence of rapidly emitted notes. We broadcast playbacks of unaltered and temporally manipulated conspecific advertisement calls to focal male individuals vocalizing within triads (comprised of closely neighbouring focal and non-focal males and a more distant, outsider male). Focal males demonstrated rhythmic entrainment and adjusted their calling behaviour to overlap their call sequences with those of their nearest vocalizing neighbour, including the unaltered conspecific playback. When presented with a playback of conspecific calls lacking the natural temporal sequence, focal males reduced the duration of the silent interval between call bouts and reduced the number of notes in the burst phase of their call bout, indicating the significance of the multi-element temporally complex call bout structure in mediating male–male vocal interactions.

Winter Territoriality of White-throated Sparrows (Zonotrichia albicollis) in Kentucky

Abstract We examined the responses of resident flocks of white-throated sparrows to unfamiliar individuals and vocalizations throughout the winter, while also examining circulating levels of the stress hormone corticosterone, to see if they paralleled behavioral changes. Concurrently, we validated identification of sparrow plumage morphs with genotype assays to determine reliability of field identification. Accuracy of field identification of plumage morphs was 68.8%. Baseline corticosterone did not differ among sampling periods, suggesting these birds did not experience prolonged chronic stress throughout the winter. However, white-throated sparrows responded more aggressively to study skins and playback of conspecific calls and songs in November than in January and March. These results suggest that agonistic displays may be more important for defending winter territories and establishing dominance status in early winter.

Vocal responses to noise reveal the presence of the Lombard effect in a frog

Many animal communication systems have evolved signal flexibility depending on environmental conditions. A common strategy of vocal communication is to increase amplitude in response to increasing noise levels. This phenomenon, known as the Lombard effect, is a widespread trait among mammals and birds. Anurans are a major group with many species that rely heavily on acoustic signals for sexual communication. Although these species often communicate in noisy environments, the presence of the Lombard effect in frogs remains unclear. We exposed male tungara frogs (Physalaemus pustulosus) to different noises with and without playback of conspecific calls. Males increased call amplitude, call rate, and call complexity in response to low-frequency noise (overlapping the species' call range) but not to high-frequency (nonoverlapping) noise. Vocal amplitude increased linearly with noise level demonstrating that tungara frogs exhibit the Lombard effect, and we discuss why different frog species may differ in their control over vocal amplitudes. Furthermore, we found the overall effect of noise to be similar to the effect of conspecific call playback. We speculate that vocal amplitude control may have evolved primarily as a response to increased competition at the cocktail party, similar to the way humans raise their voice when in a heated debate, and subsequently as a strategy to deal with background noise more generally.

An Experimental Study of the Use of Social Information by Prospecting Nocturnal Burrow-Nesting Seabirds

Abstract. Cues and social information are important in the decisions many animals make to settle. In colonial seabirds, such decisions are based upon information gathered during a prospecting phase, in which for young individuals social information from conspecifics is key. Yet the specific cues that prospectors use, and why, remain debated questions. We used an experimental approach to evaluate a conspecific-attraction hypothesis, predicting that during nocturnal prospecting Ancient Murrelets (Synthliboramphus antiquus) use social information in the form of audio cues. Specifically, we used playback experiments to test whether prospectors use conspecific vocalizations to locate potential breeding sites, and we hypothesized that prospectors' activity should increase during playback of conspecific calls. Using an information-theoretic approach we found that, as predicted, playback increased Ancient Murrelet activity, supporting a conspecific-attraction hypothesis. During playback, activity increased over b...

Do natural differences in acoustic signals really interfere in conspecific recognition in the pan-Amazonian frog Allobates femoralis ?

The call of the pan-Amazonian frog Allobates femoralis shows wide geographical variation, and males show a stereotyped and conspicuous phonotactic response to playback of conspecific calls. We evaluated the capacity of males of A. femoralis and a closely related species A. hodli to respond aggressively to natural conspecific and heterospecific calls varying in number of notes, by means of field playback experiments performed at two sites in the Brazilian Amazon. The first site, Cachoeira do Jirau (Porto Velho, Rondonia), is a parapatric contact zone between A. femoralis that use 4-note calls, and A. hodli with 2-note calls, where we performed cross-playbacks in both focal populations. The second site, the Reserva Florestal Adolpho Ducke (Manaus, Amazonas), contained only A. femoralis with 4-note calls. There, we broadcast natural stimuli of 2-note A. hodli, 3-note and 4-note A. femoralis, and 6-note A. myersi. We found that the phonotactic behaviour of A. femoralis and A. hodli males did not differ toward conspecific and heterospecific stimuli, even in parapatry. Our results indicated that the evolutionary rates of call design and call perception are different, because the geographical variation in calls was not accompanied by variation in the males' aggressive behaviour.

Detection probability of vocalizing dugongs during playback of conspecific calls

Dugongs (Dugong dugon) were monitored using simultaneous passive acoustic methods and visual observations in Thai waters during January 2008. Chirp and trill calls were detected by a towed stereo hydrophone array system. Two teams of experienced observers conducted standard visual observations on the same boat. Comparisons of detection probabilities of acoustic and visual monitoring between two independent observers were calculated. Acoustic and visual detection probabilities were 15.1% and 15.7%, respectively, employing a 300 s matching time interval. When conspecific chirp calls were broadcast from an underwater speaker deployed on the side of the observation boat, the detection probability of acoustic monitoring rose to 19.2%. The visual detection probability was 12.5%. Vocal hot spots characterized by frequent acoustic detection of calls were suggested by dispersion analysis, while dugongs were visually observed constantly throughout the focal area (p<0.001). Passive acoustic monitoring assisted the survey since detection performance similar to that of experienced visual observers was shown. Playback of conspecific chirps appeared to increase the detection probability, which could be beneficial for future field surveys using passive acoustics in order to ensure the attendance of dugongs in the focal area.

Calling Patterns in Male Responses to Conspecific Playbacks in the Johnstone’s Whistling FrogEleutherodactylus johnstonei

Vocal interactions are common in chorusing frogs. Changes in the calling patterns of Eleutherodactylus johnstonei males were analyzed by recording their responses to playbacks of conspecific calls repeated at fixed periods (long: 1.7 s, short: 0.98 s). The call period and timing, estimated through the onset response time, were determined for each male. Males reduced and regularized the period of their calls in response to both stimuli, regardless of their absolute and relative period (i.e., the difference between the male’s period and the stimulus period). Males avoided initiating their calls during ongoing stimuli, but did not time their calls in the silent gap between successive stimuli in ways that reduced the probability of overlap: the proportion of calls without overlap did not depart from random expectations when the silent gap was long, and was smaller than expected when the gap was short. This result indicated that males react to the presence of the virtual competitor but not to its particular characteristics. Fixed responses have been described in other anurans, and often relate to trade-offs between female attraction, male competition, predator attraction, and depletion of energy reserves. Lack of coordination with the stimuli, beyond inhibition of calling during an ongoing stimulus, also indicates somewhat rigid vocal strategies, at least under the experimental conditions. Results from the short period trials suggested a compromise between maintaining a call period and avoiding call overlap. Whether female behavior is influenced by call interference and whether males pay selective attention to distant males instead of to close neighbors must be investigated to better understand the vocal behavior of E. johnstonei.

Observational and Experimental Evidence for the Function of Tail Flicking in Eurasian Moorhen Gallinula chloropus

Tail movements such as wagging, flicking or pumping are reported from many bird species but their adaptive functions remain poorly understood. To investigate whether tail flicking functions as an alarm signal, either to predators or neighbouring birds, or as a signal of submission to conspecifics, I observed this behaviour in moorhen in a natural context, and conducted playback experiments using vocalizations of predators, conspecifics and heterospecifics. I found positive relationships between flicking and vigilance and nearest neighbour distance, and negative relationships between flicking and moorhen flock size and total flock size. Moorhen at the edge of a flock flicked at a higher rate. Single moorhen flicked more often compared with individuals in groups, both in single- and mixed-species flocks, and there was a tendency that single moorhen flicked more often than single moorhen within a mixed-species flock. Moorhen responded differently to conspecific and predator calls. While in both cases vigilance increased, tail flick rate was higher during predator playbacks and lower during conspecific playbacks. Furthermore, moorhen remained rather motionless when conspecific calls were played back, but not during predator calls, and, moorhen resumed to a baseline level of tail flicking more quickly after the playback of conspecific calls. Taken together, the results suggest that flicking may be considered as a honest signal of vigilance directed towards ambushing predators.

The distribution and population of the Seychelles (Bare‐legged) Scops Owl Otus insularis on Mahé: consequences for conservation

This study details the first baseline survey of the Critically Endangered Seychelles Scops Owl Otus insularis, currently only recorded from the 152‐km2 island of Mahé, the largest and highest island in the granitic Seychelles, western Indian Ocean. A survey was conducted in October 2000–March 2001 using playback of conspecific calls in random squares (500 m × 500 m) with midpoints being at least equal to 100 m asl. Playback was conducted in 159 of a possible 375 squares (42%). Territorial responses were detected in 60 of 159 (38%) squares, which represented an estimated 70 distinct territorial responses. Pairs responded in 51% and single birds responded in 49% of squares where a response was elicited. Scops Owls were more likely to be detected at higher altitudes, in mixed forest, and sympatrically with endemic frogs (Tachycnemis seychellensis and Sooglossus spp.). Two models were used to predict population: one based exclusively on altitude resulted in a population estimate of 134–159 territories (268–318 individuals) within a 34‐km2 range, whereas a second incorporating altitude and vegetation, which excluded unsuitable habitat, resulted in an estimate of 125–142 territories (250–284 individuals) in a 31‐km2 range. We discuss the implications of our findings to the Owl's conservation status and management.

The distribution and population of Seychelles Black Paradise-flycatcher Terpsiphone corvina on La Digue: implications for conservation and translocation

The 10 km2 island of La Digue, Republic of Seychelles, western Indian Ocean supports the last viable population of the Critically Endangered Seychelles Black Paradise-flycatcher Terpsiphone corvina. Small populations recorded on adjacent islands since the 1980s appear to be ephemeral and not self-sustaining. We document the results of the first island-wide survey of the flycatcher on La Digue using the playback of conspecific calls at random points. Previous surveys were based largely on counting the number of singing males. The survey was conducted between April and August 2001 and confirmed (i) the current world population is at least 200 individuals (109-145 territories, 218-290 individuals) in a c. 4.4 km2 range, thus accurately quantifying the documented increase in flycatcher numbers since the late 1970s; (ii) territories were more widely distributed than previously recorded and not exclusively associated with coastal plateaux or freshwater bodies, contrary to previous descriptions; and (iii) distribution was determined largely by the presence of high canopy (native) broad-leaved tree species. The importance of canopy height to flycatchers was highlighted by the fact that localized loss of high canopy (native) forest (4%), in a 161 ha study area on the large western plateau, resulted in an equivalent reduction (4%) in the number of territories. In light of our findings we discuss the implications for conservation of the flycatcher on La Digue and its possible translocation.

Mechanisms of heterospecific recognition in avian mobbing calls

Some birds emit special calls, referred to as mobbing calls, when they detect a predator in their area. These calls are easily localisable and function to rally other individuals to help chase out a threatening intruder. Interestingly, individuals may respond to the mobbing calls of other sympatric species. To understand the mechanism underlying interspecific recognition it is essential to determine whether birds also respond to the mobbing calls of allopatric species. If, as has been suggested, learning is important for call recognition, then calls from allopatric species should not evoke mobbing. If, however, there are intrinsic (and possibly convergent) characteristics of mobbing calls, then novel calls from allopatric species should evoke mobbing. We conducted two playback experiments with apostlebirds (Struthidea cinera, Family Corcoracidae), Australian mud-nesters, to understand mechanisms underlying mobbing-call recognition. The first demonstrated that allopatric mobbing calls could elicit a response significantly greater than control stimuli, but less than that elicited by playback of conspecific calls. The second demonstrated that the dominant frequency was critical for eliciting mobbing, rather than the commonly assumed broad bandwidth. Taken together, these results suggest that experience with a particular species' call is not essential to elicit mobbing; rather, intrinsic aspects of the calls themselves may explain heterospecific recognition.

Censusing Tawny OwlsStrix alucoby the use of imitation calls

Tawny Owls respond well to imitation or playback of conspecific calls. In 94% of known territories a response to imitation was obtained within 30 min. No measured temporal or weather variable had any effect on response time. The only factor that appeared to influence response time was population density, with birds in open farmland responding faster and more vigorously than those in continuous woodland. This is considered to be due to lack of exposure to other owls in open farmland. Female owls respond more to imitated male calls in autumn than in winter and spring. This may be due to the fact that autumn is when pair formation occurs, and females may be investigating new males. Alternatively they may be defending their territory at a time when juveniles are searching for vacancies. The findings suggest that censusing should be conducted for 30 min, at any time throughout the winter and in any reasonable weather conditions.

Male Calling Behavior in Response to Playback of Conspecific Advertisement Calls in Two Bufonids

ABSTRACr.-Previously it has been hypothesized that male anurans in breeding aggregations vocalize asynchronously to reduce acoustic overlap with neighbors. The prediction was tested that in Bufo woodhousei and B. punctatus a male will lower his call rate in response to playback of conspecific advertisement calls. Male B. woodhousei reduced their call rates in response to playback of both high and low rate recordings, although call rates were lowered to a significantly greater degree during playback of high rate recordings. Contrastingly, male B. punctatus did not reduce their call rates in response to playback of conspecific calls. Male B. woodhousei reduced their rate of calling, apparently to avoid acoustic overlap with playback recordings. Male B. punctatus, however, usually initiated a call during each call broadcast during playback, resulting in extensive acoustic overlap. In B. woodhousei, mean call rate of males in a chorus was negatively correlated with chorus size. None of the current hypotheses concerning the significance of call alternation in anurans explains these results satisfactorily.