Neighbour Stranger Discrimination Research Articles

Neighbour–stranger discrimination in an African wood dove inhabiting equatorial rainforest

We investigated within- and between-individual song variation and song-based neighbour-stranger discrimination in a non-learning bird species, the blue-headed wood-dove (Turtur brehmeri), which inhabits lowland rainforests of West and Central Africa. We found that songs of this species are individually specific and have a high potential for use in individual recognition based on the time–frequency pattern of note distribution within song phrases. To test whether these differences affect behaviour, we conducted playback experiments with 19 territorial males. Each male was tested twice, once with the songs of a familiar neighbour and once with the songs of an unfamiliar stranger. We observed that males responded more aggressively to playback of a stranger’s songs: they quickly approached close to the speaker and spent more time near it. However, no significant differences between treatments were observed in the vocal responses. In addition, we explored whether responses differed based on the song frequency of the focal male and/or that of the simulated intruder (i.e., playback), as this song parameter is inversely related to body size and could potentially affect males’ decisions to respond to other birds. Song frequency parameters (of either the focal male or the simulated intruder) had no effect on the approaching response during playback. However, we found that the pattern of response after playback was significantly affected by the song frequency of the focal male: males with lower-frequency songs stayed closer to the simulated intruder for a longer period of time without singing, while males with higher-frequency songs returned more quickly to their initial song posts and resumed singing. Together, these results depict a consistently strong response to strangers during and after playback that is dependent on a male’s self-assessment rather than assessment of a rival’s strength based on his song frequency. This work provides the first experimental evidence that doves (Columbidae) can use songs for neighbour-stranger discrimination and respond according to a “dear enemy” scheme that keeps the cost of territory defence at a reasonable level.

Horneros consider their neighbors as precious foes regardless of territory size and human disturbance

Research on neighbor-stranger discrimination theory has revealed the significance of social context and biological traits affecting the mechanisms that drive social discrimination, such as the dear enemy or nasty neighbor effects (strangers or neighbors more threatening, respectively). Nevertheless, the effects of territory size and human activity on neighbor-stranger experiments have yet to be explored. By examining behavioral responses to spontaneous duets of neighbors and playbacks of strangers’ duets, we tested whether rufous horneros (Furnarius rufus) in smaller territories show heightened aggression, responding more strongly to strangers and less to neighbors than those in larger territories. This could be expected because birds in larger territories might struggle to differentiate competitors due to limited interactions, hindering familiarity with neighbors. Meanwhile, birds in smaller territories are likely to treat neighbors as dear enemies due to the need to minimize territorial costs caused by presumed frequent intrusions or to protect limited resources. Contrary to predictions, rufous horneros responded more strongly to strangers than neighbors, regardless of owner territory sizes. This suggests that the presumed higher intruder frequency in smaller territories does not necessarily lead to adjusted dear enemy relationships. Yet, small territory holders exhibited heightened vocal responses to duets of unfamiliar intruders, indicating a stronger 'dear enemy' effect compared to birds with larger territories. We also tested whether dear enemy relationships would be heightened during weekends. This is linked to the difficulty urban birds might face in distinguishing neighbors from strangers during high human activity days (i.e., on weekdays), due to factors like noise masking intruder acoustic cues and heightened vigilance. Territorial owners exhibited consistent dear enemy behavior towards neighbors, regardless of our proxy for human activity. This underscores their ability in identifying competitor identities within urban settings.

Out of sight, out of mind: dear enemy effect in the rufous hornero, Furnarius rufus

Dear enemy and nasty neighbour are both phenomena that depend on the ability to discriminate between neighbours and strangers. Although both mechanisms reduce costs in territorial maintenance, their occurrence has been poorly investigated in duetting animals. In this study, we sought to test neighbour–stranger discrimination via cues in duets by the rufous hornero, Furnarius rufus (Furnariidae), a suboscine bird with high territorial fidelity and in which both sexes cooperate to defend the territory against competitors. Specifically, we assessed whether territorial owner aggression (1) is higher against neighbours or strangers (dear enemy or nasty neighbour effects) in the breeding and nonbreeding seasons and (2) whether aggression varies according to the intruder's position in the territory (centre versus periphery), the distance between neighbouring territories and the number of neighbours. Owners were more tolerant of neighbours' duets than of strangers' duets in the breeding and nonbreeding seasons. Furthermore, females and males demonstrated similar social discrimination abilities. The number of neighbours significantly influenced only the flight latency of the owner, and aggression against competitors was more intense at the territory centre. Aggressiveness was higher in territories whose neighbouring territorial boundaries were farther apart. Our results demonstrate that rufous hornero pairs can discriminate duets based on familiarity with the sound producers, with stranger pairs being more threatening than neighbouring pairs to resource possession throughout the year. To our knowledge, this is the first study to reveal neighbour–stranger discrimination in a duetting species. Future evaluations may reveal whether more sophisticated recognition mechanisms, such as individual recognition, are also present in this as well as in other duetting animals.

Distant neighbours: friends or foes? Eurasian beavers show context-dependent responses to simulated intruders

Neighbour-stranger discrimination is widespread in territorial animals, and depending on the relative threat posed by neighbours and strangers, residents commonly exhibit either the “dear enemy phenomenon” or the “nasty neighbour effect”. Different members of the same group may represent different threat levels, and the response of residents can be modified depending on, e.g. the sex and dominance status of the intruder. Neighbour-stranger discrimination is primarily investigated in neighbours with shared borders, and whether residents recognize their more distant neighbours remains unexplored. Here, using experimental scent marks, we investigated whether Eurasian beavers (Castor fiber) discriminate between distant neighbours (i.e. two territories away) and strangers (i.e. further away than the known dispersal distance). We tested the hypotheses that Eurasian beavers can discriminate between distant neighbours and strangers and that social status (i.e. sub-dominant or dominant) and sex of the intruder affect the responses of resident beavers. We predicted that resident beavers show the “dear enemy phenomenon” in response towards dominant distant neighbours due to their territory ownership and the “nasty neighbour effect” in response towards sub-dominants due to their likelihood to disperse. Sex of residents and social status of intruders were important in explaining territorial responses, with males exhibiting stronger responses to sub-dominant distant neighbours, especially males, than sub-dominant strangers. No such discrimination was found by females or between dominant distant neighbours and strangers. We suggest that the “nasty neighbour” response by male resident beavers towards sub-dominant distant neighbours relates to the relative threat levels due to repeated intrusions during dispersal attempts. Territorial animals discriminate between neighbours and strangers to allocate aggressive behaviour to conspecific intruders. This neighbour-stranger discrimination has primarily been investigated between adjacent neighbours, but extraterritorial movements of residents into distant territories occur. Whether residents can discriminate between distant neighbours and strangers has only been studied in skylarks (Alauda arvensis), based on acoustic communication. Yet, it is unknown whether distant neighbours are perceived as neighbours or strangers based on olfactory recognition. Here we investigated whether Eurasian beavers (C. fiber) can discriminate between distant neighbours (i.e. two territories away) and strangers, based on olfactory scent samples including information on social status (i.e. dominant or sub-dominant) and sex of the intruder. Our results show that male residents showed a “nasty neighbour” response towards sub-dominant distant neighbours. These findings highlight the sensitivity of territorial mammals to the familiarity and social status of intruders.

Response of Male Pied BushchatsSaxicola capratato Playback of the Songs of Neighbours and Strangers

Abstract Discrimination between neighbours and strangers, on the basis of acoustic cues, has been clearly demonstrated in many temperate avian species, but experiments on neighbour-stranger recognition have received less attention in tropical habitats, particularly in the Indian subcontinent. With this in mind, neighbour—stranger discrimination experiments were conducted on tropical male Pied Bushchats Saxicola caprata in the District Haridwar, of the Himalayan foothills, India. The sound levels of broadcasted songs were kept as close as possible to natural song levels. The results of the parameters analysed (including song rate, song repertoire, flights toward the speaker, distance from the speaker, and latency) did not differ significantly between neighbour and stranger song playbacks. It seems that male Pied Bushchats responded evenly toward the playback and may be incapable of discriminating between neighbours and strangers.

Territorial olive frogs display lower aggression towards neighbours than strangers based on individual vocal signatures

Some territorial animals display a form of social recognition in which they direct low levels of aggression towards established neighbours, but maintain greater readiness to respond aggressively towards unfamiliar individuals. In many taxa, such as songbirds, this so-called ‘dear enemy’ effect involves discrimination between neighbours and strangers based on individually distinctive vocal signatures. Although most anuran amphibians (frogs and toads) are highly vocal, and many are also territorial, we know very little about neighbour–stranger discrimination in this group. In the present study of the olive frog, Babina adenopleura (Ranidae), we show that the vocal signals of males are individually distinct, and that territory holders use this information to direct lower levels of aggression towards their nearby neighbours. Analyses of individual variation in advertisement calls revealed many individually distinctive spectral and temporal acoustic properties, with spectral properties contributing most towards statistical discrimination among individuals. In a field playback experiment that simulated territorial intrusions, territorial males had higher thresholds for producing aggressive calls in response to the advertisement calls of their nearby neighbours compared with those of strangers. A simple model based on sound attenuation due to spherical spreading estimated that males responded aggressively to strangers at distances that were approximately twice as far away as for neighbours and that were similar to intermale distances recorded in the field. Together, results from this study indicate that territorial male olive frogs develop vocally mediated dear enemy relationships with their nearby neighbours. These results highlight the potential for convergence in social recognition systems across diverse taxa.

Interspecific variation in neighbour–stranger discrimination in ants of theNeoponera apicaliscomplex

1. The ecological success of social insects lies in their ability to prevent the exploitation of colony resources by competitors or parasites. Nestmate recognition is therefore of crucial importance in maintaining the integrity of the colony. Furthermore, inter‐colony competitive relationships are often complex, as many species discriminate between neighbours and strangers, with reduced (the dear enemy phenomenon) or increased levels of aggression towards nearby colonies, depending on the species. In this context, between‐species comparisons could be particularly helpful to investigate the proximate causes underlying this context‐dependent phenomenon, but these are notoriously lacking.2. Here an attempt was made to circumvent this drawback by studying three closely related sympatric ant species with very similar life histories that belong to theNeoponera apicaliscomplex. The present study investigated how nestmate recognition and inter‐colony competitive relationships were influenced by spatial, chemical and genetic distances between colonies.3. It was found that one species,N. apicalismorph 7, showed a clear dear enemy phenomenon with no influence of chemical and genetic distances, suggesting the existence of a learning process. In contrast,N. apicalismorph 4 andNeoponera verenaemorph 1 failed to show any strong discrimination between close and distant non‐nestmates.4. These results are discussed in the light of the observed interspecific variation in nesting preferences, possibly constraining the opportunities of familiarisation between nearby nests, and modulating the competition for resources between colonies.5. It is argued that this study further reinforces the relative threat level hypothesis as an ultimate explanation for neighbour–stranger discrimination processes.

Large vocal repertoires do not constrain the dear enemy effect: a playback experiment and comparative study of songbirds

Many territorial animals are less aggressive towards neighbours than they are towards strangers. This phenomenon is known as the ‘dear enemy’ effect and it occurs because strangers represent a considerably higher threat to territory take-over compared to neighbours. Some evidence has suggested that large repertoires may constrain neighbour–stranger discrimination. We tested whether songbirds with large repertoires exhibit neighbour–stranger discrimination, conducting a playback study on a songbird with a large vocal repertoire, and a comparative analysis of the dear enemy effect across all published studies of songbirds. In our playback study, we broadcast neighbour and stranger songs within the breeding territories of red-eyed vireos, Vireo olivaceus, a songbird species with a large song repertoire (ca. 50 songs per individual). Vireos responded significantly more aggressively to playback of stranger versus neighbour songs; subjects approached closer to the loudspeaker, had a lower latency to approach the loudspeaker, spent more time near the loudspeaker and sang more soft songs during stranger trials than during neighbour trials. We examined song sharing between red-eyed vireos and found low levels of song sharing between neighbours, suggesting that red-eyed vireos may discriminate among conspecifics based on individually distinctive song types. We then conducted a comparative analysis of neighbour–stranger discrimination across the published literature on songbirds, using a phylogenetically controlled analysis to explore whether species with large repertoires are less likely to discriminate between neighbours and strangers. Across 34 species, we found no evidence that songbirds with large repertoires are constrained in their ability to distinguish between neighbours and strangers. We conclude that large song repertoires do not inhibit neighbour–stranger discrimination in red-eyed vireos specifically, or songbirds generally.

Individually specific call feature is not used to neighbour-stranger discrimination: the corncrake case.

In various contexts, animals rely on acoustic signals to differentiate between conspecifics. Currently, studies examining vocal signatures use two main approaches. In the first approach, researchers search for acoustic characteristics that have the potential to be individual specific. This approach yields information on variation in signal parameters both within and between individuals and generates practical tools that can be used in population monitoring. In the second approach, playback experiments with natural calls are conducted to discern whether animals are capable of discriminating among the vocal signatures of different individuals. However, both approaches do not reveal the exact signal characteristics that are being used in the discrimination process. In this study, we tested whether an individual-specific call characteristic – namely the length of the intervals between successive maximal amplitude peaks within syllables (PPD) – is crucial in neighbour-stranger discrimination by males of the nocturnal and highly secretive bird species, the corncrake (Crex crex). We conducted paired playback experiments in which corncrakes (n = 47) were exposed to artificial calls with PPD characteristics of neighbour and stranger birds. These artificial calls differed only in PPD structure. The calls were broadcast from a speaker, and we recorded the birds' behavioural responses. Although corncrakes have previously been experimentally shown to discriminate between neighbours and strangers, we found no difference in the responses to the artificial calls representing neighbours versus strangers. This finding demonstrates that even if vocal signatures are individual specific within a species, it does not automatically mean that said signatures are being crucial in discrimination among individuals. At the same time, the birds' aggressive responses to the artificial calls indicated that the information transmitted by PPDs is important in species-specific call recognition and may be used by males and/or females to evaluate sender quality, similarly like sound frequency in some insect species.

Neighbor-Stranger Discrimination On the Basis of A Threat Vocalization In the Great Black-Backed Gull

Abstract Neighbor-stranger discrimination is the ability to recognize and respond differentially to familiar and unfamiliar conspecifics. This type of recognition is common in species that aggressively defend territories, such as the colonially nesting Great Black-backed Gull (Larus marinus). This species has a large agonistic signal repertoire, which includes the “yeow,” a short-range threat vocalization. A playback experiment was used to determine whether Great Black-backed Gulls are capable of recognition on the basis of this call type. Subjects maintained alert postures for significantly longer in response to unfamiliar yeows than to those of their mates or neighbors. To my knowledge, this is the first study to demonstrate neighbor-stranger discrimination on the basis of a threat vocalization.

Neighbour–stranger call discrimination in a nocturnal rail species, the Corncrake Crex crex

The acoustic signals of birds are commonly used for individual recognition. Calls or songs allow discrimination between parent and offspring, between mates and between territorial neighbours and strangers. In this study, we investigated vocal neighbour–stranger discrimination in a nocturnally calling rail species, the Corncrake, Crex crex. We conducted interactive playback experiments with 43 males. All males were tested twice on the same night, and their responses to the calls of a familiar neighbour and the calls of an unfamiliar stranger were measured. The Corncrake males responded more aggressively to the playback of a stranger’s calls. They approached the speaker more rapidly, spent more time close to the speaker and physically attacked the speaker more frequently. We found no significant differences between the vocal responses to the playback of neighbours’ and strangers’ calls. Thus, although calling plays an important role in Corncrake territorial interactions, it is only a first line of defence in which males signal aggression towards intruders by calling, similar to singing in passerines. The lack of differences in vocal responses and the presence of clear differences in other behavioural responses demonstrate that the absence of a differential vocal response does not imply the absence of discrimination. Although the individual nature of the Corncrake call has been mentioned in a few previous studies, this study provides the first experimental evidence that Corncrake males indeed use calls for neighbour–stranger discrimination. Notably, because of the Corncrake’s dense wet meadow habitat and its tendency to signal at night, it is probable that acoustic individual discrimination in the Corncrake is crucial for making correct decisions during aggressive encounters with rivals.

Do marmots display a ‘dear enemy phenomenon’ in response to anal gland secretions?

AbstractThe ‘dear enemy phenomenon’ (DEP) is a form of neighbour–stranger discrimination in which resident territorial individuals respond less agonistically to intrusions by known neighbouring conspecifics than they do to strangers. We tested philopatric female yellow‐bellied marmots (Marmota flaviventris) for the presence of DEP. We hypothesized that dominant females discriminated between the anal gland secretion (AGS) from female neighbours and strangers, and predicted that they would respond more agonistically (as reflected by the duration of both sniffing and physical behaviour) towards AGS from strangers than neighbours. We also hypothesized that female marmots would respond differently to kin and non‐kin female neighbours, and predicted a reduced agonistic response to related individuals. Direct observations of resident marmot's responses to the olfactory trials showed that marmots spent significantly longer durations sniffing the AGS of both neighbours and strangers than a neutral scent‐free control. However, there was no significant difference in the sniffing response duration towards AGS from a neighbour or a stranger. In addition, kinship was not found to influence the responses of residents to neighbours or strangers. We conclude that, although female yellow‐bellied marmots detect AGS, they do not seem to discriminate between neighbours and strangers via AGS scent marks. Other secretions may be used in territorial identification.

Breeding density, not life history, predicts interpopulation differences in territorial aggression in a passerine bird

Interpopulation variation in territorial aggression can reflect differences in life history or competitive environments. Life history theory predicts that males with more opportunities for future reproduction should avoid risk-taking behaviour to minimize the cost of current reproduction, whereas competitive environments should favour higher aggression to defend limited resources. Additionally, male aggression can be modulated by familiarity with competitors to be either lower (dear enemies) or higher (nasty neighbours) towards neighbours. We conducted a territory intrusion experiment using neighbour–stranger songs to examine how territorial aggression differed in two populations of orange-crowned warblers, Oreothlypis celata, breeding in California and Alaska. The California population breeds at very high densities and has a higher annual survival relative to the Alaska population, which breeds at significantly lower densities and has a lower annual survival rate. We found that California males showed higher amounts of territorial aggression in response to simulated territory intrusions than did Alaska males, supporting the hypothesis that competitive environments, as indicated by breeding density, rather than life history, shape geographical variation in levels of aggression. Both populations discriminated between song stimuli of neighbours and strangers, but California males responded more strongly towards neighbours, whereas Alaska males responded more strongly towards strangers. We discuss these results in light of the mechanisms for overall aggression and neighbour–stranger discrimination.

MICRODIALECT AND GROUP SIGNATURE IN THE SONG OF THE SKYLARK ALAUDA ARVENSIS

ABSTRACT The Skylark Alauda arvensis is a territorial species of open landscape in which pairs settle in stable and adjacent territories during the breeding season. Due to the heterogeneity of the habitat, territories are gathered in patches spaced by a few kilometres, in which each male produces very long and complex flight songs as a part of the territorial behaviour. We showed that, in a given patch, all the males (neighbours) share some particular sequences of syllables in their songs, whereas males settled in different patches (strangers) have almost no sequences in common. Such a phenomenon is known as microdialect. To test the hypothesis that these shared sequences support a group signature, we made playback experiments with “chimeric” signals: songs of strangers where the sequences shared by neighbours were artificially inserted. Behavioural responses to playbacks indicated a neighbour-stranger discrimination consistent with the dear enemy phenomenon, i.e. a reduced aggression toward neighbours compared to strangers. Furthermore, the same level of responses, observed when a “chimeric” song and a neighbour song were broadcast, indicated that shared sequences are recognised and identified as markers of the neighbourhood identity.

Neighbour–stranger discrimination by Yellow-bellied Tit Parus venustulus: evidence for the “dear-enemy” effect

Neighbour–stranger discrimination has been demonstrated in many taxa, but the mechanism employed in discrimination varies across species. We tested whether an oscine bird with a small repertoire size, the Yellow-bellied Tit Parus venustulus, discriminated between songs of neighbours and strangers. We carried out playback experiments on 18 males to detect the response of each male to the song of a neighbour as well as its response to the song of a stranger. In both cases the songs were broadcast from the territory boundary shared by the subject male and the neighbour. Subjects responded more aggressively to songs of strangers than neighbours. They approached the loudspeaker faster and closer, and performed more flights during playbacks of stranger songs than neighbour songs. There were no significant differences in vocal response between treatments. We conclude that the Yellow-bellied Tit can discriminate between songs of neighbours and strangers. As there is no song-type match across subjects, neighbours and strangers, and no differences of shared song type numbers between familiar pairs and stranger pairs, we think that song characteristics may play a role in neighbour–stranger discrimination.

Vocal duets in a nonpasserine: an examination of territory defence and neighbour–stranger discrimination in a neighbourhood of barred owls

Mated pairs of animals in many taxa coordinate their vocalizations into duets, yet most research on duetting has focused on songbirds. Here we examine the duetting behaviour of barred owls (Strix varia) by addressing three questions: (1) Do owl duets play a role in territorial interactions? (2) Do owls discriminate between duets of neighbours versus strangers? (3) Do duets play a role in extended communication among a neighbourhood of owls? We simulated territorial encounters by broadcasting duets of adjacent, territory-holding owls (neighbours) and distant owls (strangers). We assessed responses to playback using a 3.5-km transect of automated recording devices. We compared vocal activity during a pre-playback period and following both playback treatments for the focal pair, their neighbours, and more distant owls within the neighbourhood. After playback, focal owls gave significantly more duets, vocalized for a longer duration, and emphasized different call types compared to the pre-playback period, demonstrating that barred owls use duets in territory defence. Focal owls did not respond significantly differently to neighbours versus strangers. At the neighbourhood level, owls did not behave differently during silent pre-playback periods or post-playback periods. Our results suggest barred owl duets function primarily in immediate confrontations during territorial conflicts.

Sharing songs within a local dialect does not hinder neighbour–stranger discrimination in ortolan bunting (Emberiza hortulana) males

[Neighbour–stranger (hereafter N–S) discrimination in birds is common and has most likely evolved to settle repeated disputes more efficiently and without physical fights. We tested whether an oscine bird, the ortolan bunting (Emberiza hortulana), with a small repertoire size from a population with a local dialect and a high level of song sharing is able to discriminate between the songs of neighbours and strangers. We performed playback experiments with eighteen males to measure the response to a repeated single rendition of a single song type derived randomly from a repertoire of a neighbour or stranger. Subjects responded more aggressively to the songs of strangers than neighbours (faster approach, more calls and songs uttered), suggesting that ortolan buntings can discriminate between the songs of neighbours and strangers. Our results also suggest that cues for N–S discrimination may be based on individual within-song type variation regardless of song-type repertoire composition. We contrast our results with an earlier study where ortolan buntings from a non-dialect population were tested. Finally, we predict a positive relationship between the level of song sharing and within-song type variation, which may be maintained by selection for N–S discrimination in songbirds with small and moderate repertoire sizes., Neighbour–stranger (hereafter N–S) discrimination in birds is common and has most likely evolved to settle repeated disputes more efficiently and without physical fights. We tested whether an oscine bird, the ortolan bunting (Emberiza hortulana), with a small repertoire size from a population with a local dialect and a high level of song sharing is able to discriminate between the songs of neighbours and strangers. We performed playback experiments with eighteen males to measure the response to a repeated single rendition of a single song type derived randomly from a repertoire of a neighbour or stranger. Subjects responded more aggressively to the songs of strangers than neighbours (faster approach, more calls and songs uttered), suggesting that ortolan buntings can discriminate between the songs of neighbours and strangers. Our results also suggest that cues for N–S discrimination may be based on individual within-song type variation regardless of song-type repertoire composition. We contrast our results with an earlier study where ortolan buntings from a non-dialect population were tested. Finally, we predict a positive relationship between the level of song sharing and within-song type variation, which may be maintained by selection for N–S discrimination in songbirds with small and moderate repertoire sizes.]

Neighbor–Stranger Discrimination in Concave‐Eared Torrent Frogs, Odorrana tormota

AbstractThe dear enemy phenomenon in which animals discriminate familiar neighbors from unknown strangers, and respond more aggressively to strangers is well established in various social animals, especially in songbirds and mammals. So far, very few studies of neighbor–stranger discrimination have been carried out in amphibians and the results have been mixed. Thus, it is unclear whether this phenomenon exists commonly in frogs and toads, and whether it is exhibited by species with large vocal repertoires. We conducted acoustic playback experiments with male concave‐eared torrent frogs (Odorrana tormota, a species with an unusually large vocal repertoire) kept in a tank in a quiet room to investigate whether or not they can discriminate strangers from neighbors acoustically. Nine of the 14 males tested showed evoked vocal responses to the calls from strangers, but none to calls from neighbors; vocal response to the calls from strangers was accompanied by aggressive motor activity. These results demonstrate that male O. tormota possess the ability to discriminate neighbors from strangers acoustically. Odorrana tormota therefore joins three ranid species (Rana catesbiana, Rana clamitans, Rana dalmatina, all known to have a comparatively small and stereotyped vocal repertoires) as the only anurans demonstrated to have this ability. Given the difference in signaling complexity between these frog species, the salient acoustic features used for discriminating neighbors and strangers are likely to be quite distinct.

Who is Calling? Intraspecific Call Variation in the Aromobatid Frog Allobates femoralis

AbstractMany territorial species respond less aggressively to familiar neighbours than to unfamiliar floating strangers based on individual differences in acoustic signals. This form of social recognition, termed neighbour–stranger discrimination (NSD) or dear‐enemy phenomenon has been reported so far from three anuran species. To investigate the potential of auditory signal features to convey information on sender’s identity, we determined patterns of within‐male and between‐male variability in the advertisement call of the aromobatid frog Allobates femoralis. We examined 285 calls from 19 males to assess those call properties showing sufficient and reliable inter‐individual differences to function as possible recognition cues. Beside calls per call bout and call rate, all other examined call properties were more variable among males than within males. Generally, temporal call features showed higher between‐ and within‐male variability ratios than spectral properties and contributed mostly to distinguish individual males in the discriminant‐function analysis. Mean classification success of 64.9% correctly assigned calls to individual males is mainly attributable to three temporal call properties (duration of note 1 and 4, note repetition rate). Altogether, our results suggest that there is sufficient variation in the advertisement call to discriminate statistically among individual males. However, assessed call differences between A. femoralis males were rather small, suggesting that potential NSD might be based either on a combination of call features or even on the whole pattern of individual call variation instead on single call properties. Habituation–discrimination experiments in the field using modified playback signals to test for differential behavioural responses are required to confirm this hypothesis.

INDIVIDUAL VARIATION AND LEK-BASED VOCAL DISTINCTIVENESS IN SONGS OF THE SCREAMING PIHA (LIPAUGUS VOCIFERANS), A SUBOSCINE SONGBIRD

One long-standing ornithological paradigm holds that song learning in oscine songbirds has a cultural component, whereas suboscine songbirds inherit songs genetically. Recent studies reveal that suboscine song may be more variable and complex than previously realized. Several suboscine species show marked individual variation in their songs—variation that may play a role in individual recognition and neighbor–stranger discrimination—and a few suboscine species show indications of song learning. We investigated individual variation in the vocalizations of a suboscine passerine, the Screaming Piha (Lipaugus vociferans), from recordings of 26 males at four lek sites along the Tambopata River in Peru. Male Screaming Piha songs consist of quiet introductory syllables followed by two explosively loud syllables that sound like an emphatic pee haw. We used three complementary methods to examine variation in song characteristics. Spectrogram cross-correlation revealed significant consistency within individual males and variability among males. Analysis of fine structural characteristics revealed that all measured song features were significantly less variable within individuals than among individuals. Canonical discriminant analysis based on these 13 song features correctly classified 93.2% of songs by individual and 76.4% of songs by lek site. Our results indicate that there is sufficient consistency in song features within males and sufficient variation among males for identification of individuals on the basis of songs and, to a lesser extent, that song features vary with the lek site of the singer. We conclude that Screaming Pihas sing songs that are individually distinctive and bear a lek signature.