Responses of collared doves to playback of coos

Dove coos are assumed to play an important role in territorial defence and mate attraction. Playback experiments of coos may provide insight into their information content. In a pilot experiment, territorial males responded strongly to playback of perch coos. We were able to quantify the response by three behavioural measurements. A second series of playback showed that the experimental set-up and the behavioural measurements were suitable to demonstrate the perception of a difference between two distinctive versions of a perch coo. A stronger response was elicited by coos containing modulated elements.     

COO TYPES IN THE COLLARED DOVE STREPTOPELIA DECAOCTO: ONE THEME,DISTINCTIVE VARIATIONS

ABSTRACT

Dove coos are known to be important for intra-specific communication in various contexts. Earlier research showed the occurrence of systematic frequency modulations for the perch- coo of the collared dove and suggested that presence or absence of these modulations might be important in communication. The present study examined the occurrence of frequency modulations and frequency use for perch-, bow- and nest-coo, as well as variation in these features between and within individuals, to assess the acoustic ‘signal space’ for this species. The occurrence of frequency modulations was high for perch- and bow-coo, but low for the nest-coo. The relative distribution of modulations over the three elements of a coo differed for the various coo types. Coo types differed also in their ‘frequency profiles’. Frequency use is correlated with the occurrence of modulations. Differences between coo- types as well as variation within a coo-type and within individuals can be described by a limited set of parameters, which may be linked to basic properties of the coo producing mechanism. As a consequence of the occurrence of modulations and their distribution over the coo-types, the acoustic differences between the coo-types are amplified. As the different coo-types serve different functions, presence of modulations increases the signal space and decreases the ambiguity of the coo types. Differences between individuals exceeded those within individuals and were largest for perch- and bow-coo, which both serve in territorial defence and mate attraction.     

Perceptual salience of acoustic differences between conspecific and allospecific vocalizations in African collared-doves

In speciation events, species-distinct vocal signals can diverge acoustically in many ways. Signal receivers have to be able to distinguish conspecific from allospecific vocalizations, and the perceptual salience of acoustic features is therefore expected to be an important factor in the evolution of such vocalizations. We tested how dissimilar the species-identifying perch-coos of 12 closely related turtle-dove species (genus Streptopelia) are, as perceived by one of its members, S. roseogrisea. With operant, psychoacoustic methods we trained six doves to respond only to their conspecific coo. Responses to the perch-coos of the 12 other dove species were used as a measure of their perceptual similarity to conspecific perch-coos. Turtle-doves differentiated between the allospecific coos: some were perceived as more similar to their own species' coo than others. With multiple regression analysis we identified three acoustic features that correlated with these differences in perceptual similarity: coo duration, minimum frequency and Wiener entropy. In contrast to findings in other bird species, duration was by far the most important feature in the discrimination between conspecific and allospecific vocalizations for S. roseogrisea. The results suggest that this is due not only to the coos of the various species differing in duration but also to a comparatively high perceptibility of the differences in duration. Copyright 2003 Published by Elsevier Science Ltd on behalf of The Association for the Study of Animal Behaviour.      

Coding in the song of the wren: importance of rhythmicity, syntax and element structure

Communication between territorial songbirds usually involves a transfer of encoded information over long distances. We would expect coding and decoding strategies to be adaptive given the constraints imposed by the habitat. We used playback to examine some song parameters important for information transfer in the wren, Troglodytes troglodytes. Six stimuli were tested with various modifications to song rhythmicity, song composition, element structure, syntax and overall song spectra. Song features encoding information essential for eliciting a territorial response seemed to be embedded in the fine structure of song elements, that is, their variations in frequency and amplitude over time. To function, this strategy must be flexible enough to accommodate the deleterious effects of habitat-induced degradation. All stimuli composed of original song elements elicited responses regardless of their other alterations. Rhythmicity seemed not to be essential for eliciting territorial behaviour. However, alterations in song rhythmicity, syntax and spectra affected territorial responses, suggesting that these nonessential song parameters do contribute to the options for discrimination. Copyright 2000 The Association for the Study of Animal Behaviour.     

To trill or not to trill? Territorial response to a heterospecific vocal trait in male collared doves, Streptopelia decaocto

Responding of individuals outside the conspecific range hasbeen largely explained by biases in sensory or cognitive systemstoward particular traits or trait values. More recently, ithas been shown that such responses might occur if individualsstill respond to signal traits that have been lost over time.However, empirical evidence remains scarce. We report a casesupporting the latter mechanism. Phylogenetic analysis suggeststhat the collared dove, Streptopelia decaocto, had lost thetrilled vocalization present in most congeneric taxa. We testedwhether males retained the ability to respond to these trillsin the context of territory defense. We synthesized trilledsongs by inserting trills from the sister species S. roseogriseainto S. decaocto songs. We show that trilled songs yielded higherresponses than did natural conspecific songs, and that the intensityof the response depended on the number of trilled elements.We also show that trilled songs elicited as strong reactionsas frequency modulated coos, which are stronger releasers ofterritorial response than are nonmodulated coos, but are notproduced by every males. Additional tests suggest that the frequencypattern is the most important feature of the trill used by males.However, it is still unknown whether reactions to trilled andfrequency modulated coos have the same perceptual basis. Toour knowledge, this study is the first report of a stronglydeviating signal that is still effective in vocal intrasexualcommunication in birds.     

Response to interspecific vocalizations is affected by degree of phylogenetic relatedness in Streptopelia doves

Owing to common descent, related species often show similarity in a number of traits, including those involved in communication. As a result signal similarity and phylogenetic distance are usually inversly related. However, similarity in signal structure need not correspond with similarity in response to such signals. We tested the hypothesis that individuals are more responsive to signals from closely related species than from distantly related ones. We conducted playback experiments on two turtle dove species (African collared-dove, Streptopelia roseogrisea, and vinaceous dove, Streptopelia vinacea) using conspecific and heterospecific vocalizations. Vocalizations were played from species that differed in degree of relatedness and in relative geographical distribution. This enabled us to separate the effects of phylogeny and those of sympatry. There was an effect of phylogenetic distance, with a decrease in response to playback stimuli as phylogenetic distance increased. The results also suggest a minor effect of sympatry, with the response to sympatric species being lower. Copyright 2001 The Association for the Study of Animal Behaviour.     

Female big brown bats, Eptesicus fuscus, recognize sex from a caller's echolocation signals

The echolocation calls of bats function in prey capture and navigation but are not commonly regarded as communicative signals. However, because bats' echolocation calls show patterns of variability, they may transmit information about a bat, such as its age, individual identity or sex. For echolocation calls to function in this manner, variation in calls must be reliably linked to the characteristics of the bat, as has been shown in a number of studies. However, few studies have asked whether bats respond to this variation. We tested whether female big brown bats can identify the sex of an unfamiliar bat from playbacks of its echolocation calls. Playback consisted of a 30-s preplayback period, a 60-s playback period of either male or female echolocation calls, and a 30-s postplayback period. In the playback and postplayback periods the vocalization rates of female bats changed significantly relative to the preplayback period depending on the sex of the playback stimulus, indicating that they could determine sex from the echolocation calls. These findings support the possibility that echolocation calls play a role in communication in big brown bats.     

Sources of Acoustic Variation in Rhesus Macaque (Macaca mulatta))Vocalizations

All species in the genus Macaca produce a set of harmonically rich vocalizations known as “coos”. Extensive acoustic variation occurs within this call type, a large proportion of which is thought to be associated with different social contexts such as mother-infant separation and the discovery of food. Prior studies of these calls have not taken into account the potential contributions of individual differences and changes in emotional or motivational state. To understand the function of a call and the perceptual salience of different acoustic features, however, it is important to determine the different sources of acoustic variation. I present data on the rhesus macaques' (M. mulatta) coo vocalization and attempt to establish some of the causes of acoustic variation. A large proportion of the variation observed was due to differences between individuals and to putative changes in arousal, not to differences in social context. Specifically, results from a discriminant-function analysis indicated that coo exemplars were accurately assigned to the appropriate individual, but vocal “signatures” were more variable in some contexts than in others. Moreover, vocal signatures may not always be reliable cues to caller identity because closely related individuals sound alike. Rhesus macaque coos evidently provide sufficient acoustic information for individual recognition and possibly kin recognition, but are unlikely to provide sufficient information about an external referent.     

Processes underlying complex patterns of song trait evolution in a Setophaga hybrid zone

During secondary contact between two species when hybrids are less fit than parents, mating signals are expected to diverge, while aggressive signals are expected to converge. If a single signal trait is used in both mating and aggression, then the dynamics between these two forces could influence the evolutionary trajectory of that trait. We studied such a situation in an avian hybrid zone between two Setophaga species, where birdsong is used in both mate attraction and territory defense. We hypothesized that song modules of the two species will show separate and distinct geographic patterns due to the influence of selective pressures for effective territorial aggression and for effective mate attraction. We conducted geographic cline analyses and playback experiments across this hybrid zone. We found an unexpected geographic pattern of asymmetric introgression of song rhythm, which may be explained by results of the playback experiments that suggest that differences in song rhythm serve a greater role in mate attraction than in territory defense. In contrast, differences in syllable morphology show little evidence of importance in mate attraction or territorial defense. Song features converge in the hybrid zone, yet patterns of trait change suggest that the song production modules may vary in their modes of development and inheritance. Syringeal motor gesturing, which gives rise to syllable morphology, shows a nonclinal mosaic pattern, suggesting that this trait may be predominantly learned. In contrast, respiratory patterning, which forms song rhythm, shows a clinal geographic transition, suggesting that this trait could be more innate. The results indicate that opposing forces act independently on song via distinct modules of the song production mechanism, driving complex patterns of song trait evolution.     

The function of duetting in magpie-larks: conflict, cooperation, or commitment?

Avian duetting is a poorly understood phenomenon despite many hypotheses as to its function. Contrary to the recent view that duetting functions for mate guarding and is a result of conflict between the sexes, Australian magpie-larks, Grallina cyanoleuca, do not use duetting as a paternity guard. I used a playback experiment to investigate the role of antiphonal duetting in territorial defence and pair bond maintenance, two traditional hypotheses about the function of duetting. The experiment showed that, like many nonduetting species, magpie-larks recognize neighbours on the basis of song. It also provided evidence of functional differences between duetting and solo singing which indicate that temporal coordination of song between partners is used to maintain the territory and pair bond. Duets were more threatening territorial signals than solo songs: males initiated more vocalizations in response to playback of duets than playback of solos. Simulated intrusion also caused males and females to approach the speaker together and coordinate more of their vocalizations to form duets. Females did not engage in sex-specific territorial defence, responding equally strongly to playback of male and female song, and maintaining both territory and pair bond by attempting to exclude intruders of either sex. Males initiated more vocalizations in response to playback of male than female song, and their likelihood of duetting appeared to be related more to threats to the pair bond, in particular desertion by their partner. Copyright 2000 The Association for the Study of Animal Behaviour.     

Song Amplitude of Rival Males Modulates the Territorial Behaviour of Great Tits During the Fertile Period of Their Mates

Bird song is a widely used model in the study of sexual selection. Variation in the expression of sexually selected traits is thought to reflect variation in male genetic and/or phenotypic quality. Vocal amplitude is a song parameter that has received little attention in the context of sexual selection, but there is some evidence that the intensity of bird song affects female preferences. Here, we tested whether the amplitude of broadcast song plays a role in male–male competition. We used song playback with varying song amplitude (within the natural amplitude range of the species) and a dummy bird taxidermy to simulate territorial intrusions in the great tit, Parus major, during the fertile period of the female and measured the response of the local male. The results show that playback amplitude significantly affected the subjects’ behaviour: after approaching to within 25 m around the loudspeaker, territorial males stayed longer within that perimeter after the playback of high‐amplitude songs compared with low‐amplitude songs. Our findings add to the small but growing body of evidence suggesting that vocal amplitude may be a sexually selected song trait.     

Alarm call‐based discrimination between common cuckoo and Eurasian sparrowhawk in a Chinese population of great tits

Morphological resemblance of the common cuckoo Cuculus canorus to the Eurasian sparrowhawk Accipiter nisus has been regarded as an example of predator mimicry. Common hosts could distinguish parasites as the result of coevolution, while rare hosts or non‐hosts may mistake cuckoos for hawks because rare hosts or non‐hosts behave similarly when faced with these two species. Birds usually produce alarm calls in addition to showing behavioral responses when in danger. However, previous studies of identification by rare hosts or non‐hosts of sparrowhawks usually lacked experimental evidence of alarm calls. Great tits Parus major, a rare cuckoo host, perform similar behaviors and usually produce alarm calls in response to sparrowhawks and common cuckoos. Here, we tested whether great tits could distinguish common cuckoo from sparrowhawk based on analysis of their alarm calls and the effects of playback of alarm calls on conspecific behavior. Previous studies showed that great tits have a complex communication system that conveys information about predators, and they could perform different kinds of response behavior to different alarm calls. If great tits have not made the ability to distinguish between common cuckoo and sparrowhawk, then their acoustic responses to these two species and their response behaviors in playback experiments should be similar. Specimens of a common cuckoo (parasite), a sparrowhawk (predator) and an Oriental turtle dove Streptopelia orientalis (harmless control) were used to elicit and subsequently record the response behavior and alarm calls of great tits. There was no significant difference in behavioral response among great tits when exposed to the dummy of cuckoo, sparrowhawk and dove. In contrast, they differed significantly in alarm calls. Great tits produced more notes per call that contained increasing D‐type and decreasing I‐type notes when responding to sparrowhawk as compared to cuckoo or dove. In playback experiments, we found that great tits responded more strongly to great tit hawk than to great tit cuckoo or great tit dove alarm calls. Our study suggests that great tits are able to distinguish sparrowhawks from common cuckoos and convey relevant information in alarm calls by adjusting the number and combinations of notes of a single call type.     

Male territorial vocalizations and responses are decoupled in an avian hybrid zone

A core area of speciation research concerns the coevolution of species-specific signals and the selective sensitivity to such signals. Signals and responses to them should be tuned to each other, to be effective in intraspecific communication. Hybrid zones are ideal to study the presence of such 'behavioural coupling' and the mechanisms governing it, and this has rarely been done. Our study examines acoustic signals of males and their response to them in the context of territorial interactions in a natural hybrid zone between two dove species, Streptopelia vinacea and Streptopelia capicola. Male signals are important in hybrid zone dynamics as they are essential for territory establishment, which is crucial for successful reproduction. We tested whether the response of individual male hybrids is linked to how similar their own signal is to the playback signal. We did not find evidence for behavioural coupling. The combined evidence from the low level of response to hybrid and heterospecific signals outside the hybrid zone and a lack of coupling within the hybrid zone suggests that perceptual learning may explain our results. Learning to respond to locally abundant signals may be the best individual strategy and is likely to contribute to the maintenance of a hybrid zone.     

Repeated decrease in vocal repertoire size in Streptopelia doves

Most bird species produce different acoustic signals in different behavioural contexts. This intraspecific variation in signal types is thought to be the result of selection for optimal communication in each context. Doves in the genus Streptopelia have three distinct behavioural contexts in which they produce coo vocalizations. Some Streptopelia species have three acoustically similar coo vocalizations associated with the three contexts, but in others the coo vocalizations differ in acoustic structure. Using a well-resolved phylogeny, we examined whether acoustic differentiation between coo types was the ancestral state. Unexpectedly, the results showed that the common ancestor of Streptopelia had differentiated coos rather than a single coo type. This result implies that context-specific acoustic signals disappeared from the vocal repertoire independently at least two times. We further tested whether different context-dependent signal types follow different evolutionary pathways and whether they differ in rate of evolutionary change. We found that the long-range signal (perch-coo) evolves at a higher rate than the short-range signal (bow-coo). These results are discussed in relation to selection for species recognition and transmission requirements.     

Two Novel Vocalizations Are Used by Veeries (Catharus fuscescens) during Agonistic Interactions

Avian vocalizations are common examples of the complex signals used by animals to negotiate during agonistic interactions. In this study, we used two playback experiments to identify agonistic signals in a songbird species with several acoustically complex songs and calls, the veery. In the first experiment, we compared veery singing behavior in response to simulated territorial intrusions including playback of three variations of veery song: 1) song alone as a control, 2) songs with added whisper calls, and 3) songs with introductory notes removed. In the second experiment, we used multimodal stimuli including songs, whisper calls and songs with introductory notes removed, along with a robotic veery mount. Focal males readily responded to all of the playback stimuli, approached the speaker and/or robotic mount, and vocalized. Male veeries gave more whisper calls, and sang more songs without the introductory note in response to all types of playback. However, veeries responded similarly to all types of stimuli presented, and they failed to physically attack the robotic mount. These results indicate that rival veeries use two different types of novel vocalizations: whisper calls and songs lacking the introductory note as agonistic signals, but do not allow us to discern the specific functions of these two vocalizations.     

Fighting talk: complex song elicits more aggressive responses in a vocally complex songbird

Song complexity in many songbirds is a trait subject to sexual selection. It is often associated with male territorial defence. Empirical studies testing differential male responses to rival song in vocally complex songbirds have, however, been scarce. We conducted playback experiments of the endemic New Zealand Tui Prosthemadera novaeseelandiae to test the aggressive response of territorial male Tui to rival songs with differing complexity levels. Overall, complex songs evoked significantly stronger responses from territorial males than did simple songs. Following playback of complex songs, focal males approached the playback more closely and rapidly, and responded with songs of higher complexity than they did to playback of simple songs. This suggests males could both distinguish between different levels of complexity within the Tui repertoire, and perceive a more complex song as a greater territorial threat. Our study is one of the first to demonstrate strong aggressive responses to increased levels of song complexity in a songbird species with highly complex vocalizations.     

Hybrid vocalizations are effective within, but not outside, an avian hybrid zone

Secondary contact between closely related species can lead tohybridization. The fitness of hybrid individuals within andoutside the hybrid zone determines whether the hybrid zone expandsinto the ranges of the 2 parental species or remains a stable,geographically narrow area in between the allopatric rangesof the parental species. In birds, vocalizations play an importantrole in male–male competition and female mate choice andare often affected by hybridization. One of the factors thatwill influence male hybrid fitness is the ability to defenda territory against competitors by vocalizing. We tested theefficacy of territorial signals of hybrids of 2 dove species,Streptopelia vinacea and Streptopelia capicola, compared withthe vocalizations of the parental species. With playback experiments,we assessed the response to hybrid and the 2 parental speciesvocalizations in the hybrid zone and adjacent allopatric populationsof each species. In the hybrid zone, males did not respond differentlyto the 3 vocalization types. In both allopatric populations,however, males responded more to conspecific than to heterospecificsignals and the response strength to hybrid signals was intermediate.Therefore, in the allopatric populations, hybrid males may havea reduced success in defending territories. In male–maleinteractions in the hybrid zone, hybrids may not have a disadvantagecompared with males of the parental species. The ability todefend a territory against competitors may thus help maintaina stable hybrid zone in the area of overlap.     

Importance of Frequency and Temporal Song Matching in Black-Capped Chickadees: Evidence from Interactive Playback

Song-type matching during territorial contests may allow males of some bird species to direct their signal to a particular receiver. By matching the song-type and also responding immediately to a rival (temporal matching), a signalling male may indicate his willingness to escalate the contest. Black-capped chickadees ( Poecile atricapilla ) sing a single song-type, but are able to sing this song over a wide range of absolute frequencies. By using interactive playback to instigate and control the level of matching during trials, we investigated whether matching the frequency and the temporal patterning of song escalates contests. Males that were matched for both the frequency and the temporal pattern of their songs during trials escalated contests more than males that were not matched, while males that were only matched temporally had an intermediate response. During trials that consisted of temporal matching only, focal males often shifted frequency to match the playback. Our results confirm that frequency matching and temporal matching using a single song-type allows graded signalling during aggressive interactions in chickadees.     

Dual Function of Chip Calls Depending on Changing Call Rate Related to Risk Level in Territorial Pairs of White‐Eared Ground‐Sparrows

Different mechanisms have been proposed for encoding information into vocalizations: variation of frequency or temporal characteristics, variation in the rate of vocalization production, and use of different vocalization types. We analyze the effect of rate variation on the dual function of chip calls (contact and alarm) produced by White‐eared Ground‐sparrows (Melozone leucotis). We conducted an acoustic playback experiment where we played back 1 min of four chip call rates (12, 36, 60, 84 calls/min). We measured the response of territorial pairs using behavioral responses, and fine structural features of calls produced in response to those playbacks. White‐eared Ground‐sparrows showed more intense behavioral responses to higher than lower call rate playbacks. Both individuals of the pair approached the source of the playback stimulus faster, produced the first vocalization faster, produced more vocalizations, and spent more time close to the stimulus in higher call rate than in lower call rate playbacks. Frequency and duration characteristics of calls (chip and tseet) were similar in response to all call rate playbacks. Our playback experiment elicited different intensity of behavioral responses, suggesting that risk‐based information is encoded in call rate. Our results suggest that variation in the rate of chip call production serves a dual function in this species; calls are used at lower rates for pair contact and at higher rates for alarm/mobbing signals.     

Social stimulation of dawn singing in Dusky Flycatchers: a serendipitous experiment

Hypotheses regarding dawn singing in birds remain largely unsupported by quantitative data, especially for suboscine passerines (suborder Tyranni). During a study of the singing behavior of a suboscine, the Dusky Flycatcher (Empidonax oberholseri), in Alberta, Canada, spring storms in 2002 caused the disappearance and presumed mortality of several territorial males and some of their replacements, creating a serendipitous experiment. Overall, 15 males disappeared and, as a result, the number of territorial males in our study area declined from 13 prior to the storms to six afterward. Only one male maintained the same territory throughout the breeding season. During the period of inclement weather and social instability (20 May to 9 June), males sang at high rates during the predawn period. From 10 to 19 June, following this period of unstable weather and turnover in territorial males, males began dawn singing later in the morning, and sang shorter bouts at lower rates. The proportion of males engaging in dawn singing also decreased between the two periods. In contrast, daytime singing activity of paired males was low during both time periods. Playback of dawn songs to territorial males between 20 June and 21 July caused a resumption of some dawn singing. Singing rates were higher on the day of playback than on the day before playback, and the times when dawn singing was initiated were earlier on each of 2 d after playback than on the day before playback. In addition, the proportion of males engaging in dawn singing increased between the day before and the day after playback. Both the decrease in dawn singing when population density was reduced and its partial restoration by playback suggest that dawn singing in this species functions in male–male interactions and support the social‐dynamics hypothesis as an explanation for the dawn chorus in this species.