Ibis

American Crows (Corvus brachyrhynchos brachyrhynchos) are long-lived birds with pair bonds that may last many years. Pairs in Stillwater, OK, nested singly or in groups with up to 10 auxiliaries (Caffrey and Peterson 2015). Breeders did most of the nest building. Pair members contributed at approximately equal rates, although the sexes differed slightly in details: males tended to carry sticks and hand off materials more often, and females spent more time at and in nests. Both sexes worked faster on second and third attempts than on first attempts of the season. We found no evidence that pair members were (sexually) signaling to each other via their contributions. Incubation periods were characterized by low levels of activity at nests, where females spent most of their time and were fed once every 3-4 hours, mostly by their mates. Contributions to both stages of nesting by auxiliaries varied widely and exhibited no patterns with respect to any measured phenotypic characteristics.

While the function of bird song has been well studied in male songbirds, the function of female song is less well understood. This is partly due to a historical view of females occupying a passive role compared with males, which led to ignoring female song even in some well-studied species. We report one such case in yellow warblers (Setophaga petechia), as no other study investigated female song in 35 years after the first documentation of solo female songs. We interrogate the seasonal patterns and functions of female song in Galapagos yellow warblers (Setophaga petechia aureola), in which females perform solo song and produce duets with their male social partners. We carried out simulated territory intrusions by broadcasting male, female, or duet songs during breeding and non-breeding seasons, and conducted a territory retention survey for over a year. We measured the association between aggressive response and singing behaviour, sex-specific patterns of response, and territory retention across years. Females sang mostly during the non-breeding season and predominantly in male-led duets. Although females were strongly aggressive towards female song playback, they gave the weakest singing response towards them. There was no association between female aggressive behaviour and song output in response to a simulated intruder. Moreover, the probability of territory retention across years was not explained by song output or aggression in response to intruders, though evidence for this was weak due to the small sample size. We suggest that female song in this year-round resident island system does not function for territory defense or intrasexual competition, but may have other functions. HighlightsO_LIGalapagos Yellow Warbler females produce solo songs and duets with their male partners. C_LIO_LIFemale song and aggression were mainly restricted to the non-breeding season. C_LIO_LIWhile females were equally aggressive to all intruders, they had the lowest song rate in response to females. C_LIO_LIIn contrast to males, aggressive behaviour didnt predict song output in females. C_LIO_LIFemale singing behaviour did not increase the probability of territory retention. C_LI

The vocalizations of many songbirds have been well documented and analyzed, but less is known about the vocal behavior of many non-passerines, including swifts. When flying alone and during aerial displays with conspecifics, Chimney Swifts (Chaetura pelagic) often utter a twitter call consisting of a series of high-frequency chip notes. However, little is known about the possible function(s) of swift flight displays and their twitter call. Our objectives were to record, analyze, and document the aerial behaviors and associated vocalizations of adult Chimney Swifts. We studied in Madison County, Kentucky, where they used abandoned, concrete shelters for roosting and nesting. Camcorders were used to record swift behavior and vocalizations during the 2008 and 2009 breeding seasons (April - September). We examined possible variation in the characteristics of swift vocalizations and the frequency of different aerial behaviors among breeding stages and behavioral contexts. Chimney Swifts engaged in more interactive pair flights during the nest-building/egg-laying stage, when females are likely fertile, and significantly more than during the pre-building and nestling stages, suggesting the possible importance of pair flights in courtship, pair bonding, and mate-guarding. Our results also suggest that V-ing (a raised-wing display) may be important in establishing or maintaining pair bonds because swifts engaged in this behavior more frequently during close chases involving two birds. We separated the typical swift twitter into two bouts: "steady" bouts and "quick" bouts. Mean chip rates were higher for the quick portion of the call, but we found no differences in the use of steady and quick bouts among nesting stages or in different behavioral contexts. Mean chip rates for quick bouts were highest for single birds and lowest for two and three birds, suggesting that twitter calls provide information about a birds location; to help coordinate movements while flying near others (e.g. when foraging and during chases), We were unable to identify individual swifts; such identification would facilitate the investigation of individual variation in call characteristics (e.g. chip rate and steady/quick bout rate) and relationships between and among swifts engaging in different activities and flight displays.

Heterospecific communication is common for birds when mobbing a predator. However, joining the mob should depend on the number of callers already enrolled, as larger mobs imply lower individual risks for the newcomer. In addition, some community informant species seem more reliable regarding the information transferred in mobbing calls. Birds should therefore rely on both the number of callers and the species identity of the caller(s) when mobbing. In the present study, we tested the potential interaction between two acoustic cues. In a playback experiment, we modified the number of callers (through an increased number of calling individuals correlated to an increased duty cycle) and the emitter species (crested tits versus coal tits). Overall, we found that soundtracks with three callers triggered more mobbing than soundtracks with one caller and that soundtracks with coal tits calls triggered more mobbing than soundtracks with crested tits calls. Our results therefore support the hypothesis that birds consider both the species and the number of callers when joining a mobbing chorus in winter. Finally, we replicated the experiment in spring and did not record the same responses from the bird community. Indeed, only soundtracks with three coal tits triggered a mobbing response, suggesting therefore that the seasonal context can affect the results of studies on heterospecific communication. The potential mechanisms implicated in the varying responses to different acoustic cues and different seasons are discussed and should deserve further investigations.

Breeding pairs of American Crows (Corvus brachyrhynchos) in Stillwater, OK, lived with 0-10 auxil-iaries in territories distributed throughout public, campus, commercial, and residential areas. Unpaired crows moved easily among groups throughout the year, but commonly did so during the two months or so preceding the onset of nesting across the population, and the week or so preceding hatching within groups. In 2001 and 2002, pre-hatch group size ranged from 2-10 (mean = 4.5 in both years), and auxiliaries included a male sibling, social and genetic offspring, step-offspring, half-siblings, and unrelated immigrants of both sexes, ranging in age from 1 to at least five years old. Twenty nine percent of pre-hatch auxiliaries dispersed out of groups at hatch-ing (for half, only temporarily), including all females unrelated to female breeders. Post-hatch group size ranged from 2-6, with means of 3.7 in both years, and the post-hatch auxiliary popula-tion differed in composition from the pre-hatch population: whereas post-hatch male auxiliaries included a sibling, half siblings, and unrelated immigrants in addition to social and genetic sons, all post-hatch female auxiliaries were the social and genetic daughters of female breeders, and all but one (the same individual in both years) were also the social and genetic daughters of male breeders. Crows in Stillwater delayed breeding for one or more years beyond sexual maturity, despite the availability of space and members of the opposite sex. Individual dispersal decisions by unpaired crows, and the behavior of paired territory owners, did not follow patterns described for other cooperative breeders. We found little support for extant theories regarding the formation, com-position, and maintenance of avian groups, and discuss aspects of the lives of crows that may have contributed to the complex and benign nature of this populations society. How to Cite: Caffrey, C. and C. C. Peterson. 2015. Group composition and dynamics in American Crows: insights into an unusual cooperative breeder. Friesen Press.

Animal vocal communication ranges from simple to complex based on repertoire size, structure, and composition of calls and the information encoded in them. According to the social complexity hypothesis, communication complexity tends to increase with an increase in social complexity. While several studies on mammalian systems exist supporting this, evidence from avian systems is comparatively limited. Towards this, we present evidence for complex acoustic communication in a cooperatively breeding passerine, Jungle Babbler, based on three aspects of complexity: an extensive repertoire of acoustically-distinct calls, within-call structural complexity and the diverse behavioural contexts in which these calls are used. Jungle Babblers were found to possess a structurally and functionally diverse vocal repertoire comprising 15 different calls. Detailed acoustic analyses of multisyllabic calls revealed that these calls are composed of different notes. Further, despite a large number of notes present in the repertoire, the number of calls were limited to 15. This implies that there may be underlying rules that determine call composition to give rise to functional calls to which receivers respond. We also found that these calls were produced in a variety of affiliative and agonistic contexts and were employed towards coordination of diverse social behaviours including group movement, foraging, brood care, aggression and vigilance. Yet, 7 out of 15 vocalizations were produced in the context of vigilance. This disproportionate investment of vocalizations towards co-ordinated acoustic vigilance is characteristic of many cooperatively breeding birds. Our study extends support for the social complexity hypothesis and also lays the foundation for future investigations on combinatorial and syntactical rules underlying call structure and function in bird vocalizations. Significance statementStudies on vocal complexity in birds have focussed mainly on repertoire size, structure and function. However, fine temporal and spectral features of elements that constitute a call/song are rarely examined to evaluate vocal complexity. We examined complex communication in a cooperatively breeding social passerine, Jungle Babbler for which we assessed repertoire size, function, acoustic features of calls and of their constituent elements. Jungle Babblers were found to possess a structurally and functionally diverse vocal repertoire comprising of 15 calls, 46% of which were in the context of vigilance, thereby extending support to the social complexity hypothesis. We also found that several calls were composed of multiple, acoustically distinct notes. These findings will be foundational in understanding the interrelations between sociality and communicative complexity and underlying combinatorial rules that determine call structure and function.

Inter-individual recognition is crucial for stable social relationships and it is frequently mediated through vocal signatures. In socially complex species, recognition may additionally require additional levels corresponding to other layers of social organisation such as the pair, family, social group or colony. Additional vocal signatures may encode these different levels of social organisations for recognition. We investigated this hypothesis in the calls of the rook (Corvus frugilegus), a highly social corvid. Rooks form large breeding colonies where multiple pairs nest in clusters. We recorded the calls of five colonies located in France and in Great Britain, including both wild and captive colonies. To exclude variations due to different call types, we focused on the loud nest call produced exclusively by nesting females during the breeding season. We compared the acoustic distance of calls from each individual and between individuals at various levels of nest proximity, i.e. from the same nest cluster, from different nest clusters, from colonies within the same country, and from colonies in different countries. The only vocal signatures we found were at the individual level, but not at the nest cluster or colony level. This suggests a lack of vocal convergence in this species, at least for the nest call, which may be important for pair recognition in large colonies. Further studies should now evaluate if types of calls other than the nest call better carry vocal signatures as markers of different layers of sociality in this species, or if vocal divergence is a more general vocal phenomenon. In that case, applying new methods of monitoring vocal signatures in wild individuals should help understand the cognitive, social and environmental mechanisms underlying this vocal singularisation. 1. Significance statementInter-individual recognition is crucial for social relationships in animals, and is often mediated by individual-specific acoustic characteristics in vocalisations, called a vocal signature. High levels of social organisations, such as a social group of familiar conspecifics or a breeding colony, may likewise be signalled by vocal signatures shared by multiple individuals. We used machine-learning techniques to investigate vocal signatures at multiple social levels in the nest call of brooding female rooks, a corvid species that breeds colonially but lives year-round in social groups. We find evidence of a strong individual vocal signature, but no common vocal signature even in females that nest close together, or in the same colony. A strong individual vocal signature may be a potent tool to monitor populations in this species with minimal disturbance and minimal material, especially as corvids are frequently targeted by human-fauna conflicts in continental Europe.

Conspecific brood parasitism (CBP) has been reported in many altricial avian species, yet its prevalence and underlying behavioural mechanisms remain poorly understood. We studied CBP in the barn swallow (Hirundo rustica), a species in which conspecific brood parasitism has been reported. We conducted parentage analysis on 1945 barn swallow broods involving 7816 offspring. Samples were collected over 12 breeding seasons at 5 colonies/populations. Contrary to expectations, we identified only six cases of CBP (0.3 % of broods). By identifying all individuals involved, i.e. the parasitic females, the female hosts and the males that fathered the parasitic eggs, we determined these cases of CBP resulted most likely from either a failed nest take-over (three times), the disappearance of a female partner or a disruption caused by researchers while only one case could be interpreted as a result of females mixed reproductive tactic. Based on a review of the literature on CBP in seven other Hirundinidae, we conclude that the only reliable evidence for CBP comes from cliff swallows (Petrochelidon pyrrhonata). Studies on other species either failed to identify the parasitic females or do not present sufficient evidence supporting the occurrence of CBP. Several studies relied on the appearance of two eggs in a nest within 24 hours to conclude that CBP occurred. However, based on the parentage analysis, we show that CBP only occurred in one out of 11 such cases in our barn swallow data. Our findings highlight that CBP is rare in our barn swallow populations, and have been likely overestimated in other studies. We emphasize the importance of frequent nest checks and rigorous genetic validation in CBP research. Overall, our results challenge existing assumptions about the prevalence of CBP and provide insights into the behavioural mechanisms that lead to CBP, with ecological and evolutionary implications.

Animals often communicate with each other in noisy environments where interference from the ambient noise and other signallers may reduce the effectiveness of signals. Signalling behaviours may also evolve to interfere with signals of their opponents, e.g. by temporally overlapping them with their own, such as the song overlapping behaviour that is seen in some songbirds during aggressive interactions. Song overlapping has been proposed to be a signal of aggressive intent, but few studies directly examined the association between song overlapping and aggressive behaviours of the overlapping bird (the predictive criterion). In the present paper we examined the question of whether song overlapping is correlated with aggressive behaviours displayed during a simulated territorial intrusion in a population of great tits (Parus major) living in an urban-rural gradient. We also examined whether aggressive behaviours are correlated with the ambient noise levels. We found that overlapping was associated negatively with aggressive behaviours males displayed against a simulated intruder. These results fail to support the predictive criterion for song overlapping, raising the question whether overlapping is in fact a signal of aggressive intent. Ambient noise levels were associated positively with aggressive behaviours but did not correlate with song rate, song duration or song overlapping. Great tits in noisy urban habitats may display higher levels of aggressive behaviours due to either interference of noise in aggressive communication or another indirect effect of noise.

Anthropogenic noise may disrupt signals used to mediate aggressive interactions, leading to more physical aggression between opponents. One solution to this problem is to switch signaling effort to a less noisy modality (e.g., the visual modality). In the present study we investigate aggressive behaviors and signaling in urban and rural male European robins (Erithacus rubecula) in response to simulated intrusions with or without experimental noise. First, we predicted that urban birds, living in noisier habitats, would be generally more aggressive than rural birds. We also predicted that during simulated intrusions with experimental noise, robins would increase their physical aggression and show a multi-modal shift, i.e., respond with more visual threat displays and sing fewer songs. Finally, we expected the multi-modal shift in response to noise to be stronger in urban birds compared to rural birds. The results showed that urban birds were more aggressive than rural robins, but an increase in aggression with experimental noise was seen only in the rural birds. Urban but not rural birds decreased their song rate in response to noise. Contrary to the multi-modal shift hypothesis, however, there was no evidence of a concurrent increase in visual signals. These results point to a complex role of immediate plasticity and longer-term processes in affecting communication during aggressive interactions under anthropogenic noise. Significance StatementHuman activity has an enormous effect on wildlife, including on their social behavior. Animals living in urban areas often tend to be more aggressive than those living in rural areas, which may be due to urban acoustic noise making communication between individuals more difficult. In a study with a common songbird, the European robin, we investigated the role of urban acoustic noise in aggression and territorial communication. Urban robins were more aggressive than rural robins, and additional noise in the territory increased aggression in rural but not urban robins. While urban robins decreased their singing effort with additional noise, they did not increase visual signals concurrently. These results suggest that noise can indeed make animals behave more aggressively although the effect may depend on how noisy it is already. These results further our understanding of how human-made noise changes animal communication and social behavior.

Mixed-species flocks (MSF) represent an important form of social organisation in bird communities worldwide. Despite its likely importance in flock formation and cohesion, the role of vocal communication in the formation and maintenance of MSF in birds is hitherto understudied. In this study, we examine if a species centrality within a mixed-species flock is influenced by its vocal behaviour during the dawn chorus, i.e., the time of MSF formation. Using acoustic sampling and field observations, we studied the bird species found in MSF in the Eastern Himalayas. Our results show differential vocal activity patterns among MSF-forming bird species and suggest a positive correlation between calling rates and closeness centrality (species importance in a flock) in understory MSFs. We also found a more synchronised vocalisation pattern in the understory MSFs, with a consistent peak in vocal activity in the early morning hours, whereas no consistent vocal pattern was found for canopy flocks. Overall, our results suggest a potential mechanism that drives MSF formation wherein the vocal activity of central species precedes and likely attracts participation from other attendant species.

Many empirical studies have focused on highly-ornamented species to identify ecological factors that maintain the ornamentation or favour its exaggeration. By contrast, although reduction or loss of ornamentation appears to be widespread, species with reduced/lost ornamentation and its relationship with ecological factors are rarely focused on. Here, based on data collected over four years, we studied outermost tail feather length, i.e. a well-known sexual ornamentation in this clade, in relation to roosting location in the Pacific swallow Hirundo tahitica during winter. In contrast to congeners, this species has inconspicuous tail ornamentation, i.e. very shallowly forked tails with vestigial streamers, providing a rare opportunity to study the ecological factors driving reduced ornamentation. We found that Pacific swallows mainly roost in old nests under bridges over rivers, which resemble their original roosting sites, but some roost in old nests under the eaves of houses above the ground. Individuals roosting under the eaves of houses had significantly longer outermost (but not central) tail feathers than those roosting under bridges. Individuals roosting under the eaves of houses were heavier and showed lower physiological stress, and thus might better endure the maintenance cost, favouring ornament elaboration. Because we controlled for the effects of sex and age, these factors would not confound the observed pattern. Reduced ornamentation, as found in Pacific swallows roosting under their original roosting sites, could become elaborated in benign environments (i.e., under eaves, here), stressing the importance of balance between the costs and benefits of ornamentation.

Vocal distinctiveness is expected to occur more often in colonial-breeding species as the parents need to recognize their offspring in a large group of conspecifics. Territorial species like the Scops Owl are expected to exhibit low distinctiveness. Contrary to what was expected, spectrographic analysis of the food-begging calls of young Scops Owls revealed previously unknown, complex acoustic structure. Within recording sessions, call duration exhibited the highest repeatability (average R 0.82), followed by the peak frequency in the last third of the call (0.61). Other spectral measures showed low to moderate repeatability (0.32 - 0.57), while the time between subsequent calls was the least repeatable (0.15). When comparing recordings made on different nights, Linear Discriminant Analysis assigned 55.7% of the calls to the correct individual, and 73.1% when restricting analysis within broods. When analyzing variability across recordings, individuals explained most of the variation in Call duration and Peak frequency in the last third of the call (89.5 % and 81.2 %, respectively), while recordings explained little variation (3.4 % and 1.3 %, respectively), suggesting that those acoustic features were the most important in vocal stability and distinctiveness. The calculated information capacity HS was 4.48 bits, i.e. within the range of values found in loosely-colonial species. The results suggest that the vocalizations of young Scops Owls show moderate individuality that could only help offspring recognition among a small number of individuals. However, the functional significance of call distinctiveness remains unclear; a few hypotheses are discussed. Keywords: Acoustic signature, coloniality, fledglings, individuality, Otus scops, repeatability.

Songbirds sing different song types depending on the social context. Songs can be categorized into two types based on their timing relative to other birds songs: solo and temporally-over-lapping songs. Overlapping songs have been typically characterized in the breeding season, in which they are associated with an aggressive social context. However, whether both song types occur year long, and whether they show differential modulation of their frequency and properties during the transition between the non-breeding and the breeding season has been rarely studied. Here we investigate, in a group of domesticated canaries (Serinus canaria), the variation of singing in both song types at the transition between the nonbreeding and the breeding season. We found that both song types were present outside the breeding season. Whereas for solo songs, duration and its variability, fraction of time singing and number of songs increased as the breeding season approached, overlapping songs showed opposite trends. Furthermore, both song types were distributed more homogeneously as the daylength increased. Overall, the differential changes of both song types at the seasonal time scale suggest differential underlying mechanisms and functions of these two song types found in a social setting.

Geographic differences in vocalisations provide strong evidence for animal culture, with patterns likely arising from generations of social learning and transmission. The current knowledge on the evolution of vocal variation has predominantly focused on fixed repertoire, territorial song in passerine birds. The study of vocal communication in open-ended learners and in contexts where vocalisations serve other functions is therefore necessary for a more comprehensive understanding of vocal dialect evolution. Parrots are open-ended vocal production learners that use vocalisations for social contact and coordination. Geographic variation in parrot vocalisations typically take the form of either distinct regional variations known as dialects or graded variation based on geographic distance known as clinal variation. In this study, we recorded monk parakeets (Myiopsitta monachus) across multiple spatial scales (i.e. parks and cities) in their European invasive range. We then compared calls using a multi-level Bayesian model and sensitivity analysis, with this novel approach allowing us to explicitly compare vocalisations at multiple spatial scales. We found support for founder effects and/or cultural drift at the city level, consistent with passive cultural processes leading to large scale dialect differences. We did not find a strong signal for dialect or clinal differences between parks within cities, suggesting that birds did not actively converge on a group level signal, as expected under the group membership hypothesis. We demonstrate the robustness of our findings and offer an explanation that unifies the results of prior monk parakeet vocalisation studies.

When biological invasions by animals occur, the individuals arriving in novel environments can be confronted with unpredictable or unfamiliar resources and may need social interaction to improve survival in the newly colonized areas. Gathering with conspecifics and using social information about their activities may reveal the location of suitable feeding and breeding sites. This could compensate for the absence of individual information about new habitats and constitute an advantage for new settlers. If a tendency to gather in response to social stimuli is transmitted from one generation to the next, and if the benefit of gathering is lower in long time established populations, there should be behavioural differences in receptivity to social cues in populations with different colonizing histories. We hypothesized that individuals of a social species like the European starling from relatively recently-established populations would be more responsive to social cues than individuals belonging to long-established populations. We conducted playback experiments using a starling chorus to test its acoustic attractiveness to populations of starlings with different colonizing histories. We compared the reaction of individuals from two populations in rural Brittany, western France, established for a long time, with three more recently settled ones: two populations from a propagation front in southern Italy and one urban population from Rennes city in Brittany. Our data supported our hypothesis: individuals from more recent populations were more responsive to the acoustic stimulus, and gave more calls in flight than individuals from populations with an older settlement history. We discuss the different behavioural responses we observed in the different populations and the potential effects of habitat characteristics and starling densities.

How song repertoires vary within species and change over time is well studied in male songbirds. However, variation in female song repertoires remains largely unstudied despite female song being much more common and complex than once assumed. We investigated the song syllable repertoire of the New Zealand bellbird (Anthornis melanura), a species where both sexes have complex but sexually dimorphic song. We compared songs at individual and population levels to investigate sex and temporal variation of syllable repertoires. We detected 96 syllable types in the population over four years, of which 58% were unique to males, 32% unique to females and 9% were shared between the sexes. The population syllable repertoire of both sexes changed substantially across years with similar turnover rates (Jaccards similarity coefficients; female 52.9-69.0%; male 58.6-73.7%). Furthermore, many syllable types, unique to each sex, varied in prevalence within the population across years. The syllable repertoire sizes of individuals were higher for males than females (13-32, n = 7 and 6-16, n = 8, respectively). Although these sample sizes were low, the temporal variation in syllable prevalence and turnover for individuals were similar to patterns at the population level. Overall, male and female bellbirds exhibited similarities in temporal patterns of yearly repertoire composition, with rapid changes in syllable prevalence, but females had fewer syllable types than males. We suggest that these similarities and differences are consistent with male and female song repertoires being driven by similar but not identical selection pressures.

Songs play an important role in mate choice for many bird species. Females of some species prefer mates with song characteristics such as complexity, or with specific temporal or note features. In some species, females also prefer familiar songs, or songs that are acoustically similar to those of their fathers. These different aspects of songs may provide distinct information about the birds that produced those songs. For example, perceived familiarity may be a signal of local adaptation, locally relevant information or learned behaviours, or genetic compatibility, while song complexity may be a signal of overall genetic quality or ability to provide parental care. As a result, multiple axes of variation could influence female song preferences. We examined female preference for song familiarity and complexity using the Java sparrow (Lonchura oryzivora) as a model species. Females were presented with two pairs of song stimuli. In one pair one song was from the females father or from a social relative with an acoustically similar song and the other was unfamiliar. In the other pair the songs differed in two aspects of complexity: note repertoire and linearity. Females preferred their fathers songs over unfamiliar songs, but we did not find strong evidence that females generalized this preference to other socially related individuals. Females also preferred complex songs, specifically those with larger note repertoires and lower linearity. Our results suggest that female song preference in Java sparrows is multi-faceted, and females may obtain multiple kinds of information from male song.

Competitive interactions among conspecifics are often resolved by assessing signals that honestly indicate individual fighting ability or dominance. In territorial species, signals of competitive ability are thought to function primarily during the early stages of territory establishment, but recent evidence suggests that these signals continue to influence interactions with floaters and neighbors well after territory establishment. Here, we examine the influence of the extent of chest spotting displayed by an intruding male on the response of territorial male song sparrows. We exposed males to 3-D printed models with large or small spotting area coupled with conspecific playback and recorded their behavior. We also assessed the response of a subset of males to both the 3-D printed models and a traditional, taxidermic mount to ensure the 3-D models were a realistic stimulus. We found no differences in the number of attacks or proximity to the model due to spotting area. However, territorial males produced more soft songs and tended to sing fewer loud songs, both of which predict attack in our population, in response to the model with less chest spotting. One possibility is that males with less chest spotting elicit a stronger response because they are seen as a greater threat. Based on our previous findings in this system, we think it is more likely that models with less chest spotting are perceived as subordinate and therefore easier to defeat, leading to a stronger response by territory holders. We found males were equally likely to attack 3-D printed models and a taxidermic mount but signaled more aggressively during trials with the taxidermic mount than the 3-D printed models. This suggests that birds recognized the 3-D models as meaningful stimuli but that the use of 3-D printed models should be validated through comparison to a traditional taxidermic mount when possible.

The temporal structure of an animals vocal output can be cognitively controlled, presenting an interesting aspect for vocal learning species that benefit from diversification. Although birdsong is the most thoroughly studied aspect of animal communication, its rhythms remain largely unknown. Here, we revisit the question of vocal individuality in the songs of male yellowhammers (Emberiza citrinella) purely from a rhythmic perspective. Yellowhammers use simple songs composed of two phrases: the initial phrase, with one individual usually having a repertoire of on average two such phrase types, and the dialect phrase containing the dialect that is the same for all males at a given locality. Some of the initial phrases are commonly shared between various males, but their combinations and frequency contours are individually unique and temporally stable. Using focal recordings of 38 known individuals, collected over three years in the same geographic location, we calculated a set of nine temporal indices to describe each song and compared individuals in a permuted discriminant function analysis. Subsequently, we calculated the potential for individual coding for each of these parameters. To assess whether rhythmic similarity may depend on the singers proximity, we calculated vocal dissimilarity as the Euclidean distances between each two males, and used Kendalls correlation. We show that yellowhammer males use individual rhythms, maintained over different phrase types and carried mostly in the inter-onset-interval variability and syllable rate, as in syllables per second, within the song. There were particularly strong rhythmic differences between singers among the closest neighbours, which decreased over the first 600 m. There was no pattern for neighbours beyond this distance. This study is the first to demonstrate the existence of strong individuality based purely on rhythm, as well as rhythmic differentiation from neighbours, in a songbird. O_FIG O_LINKSMALLFIG WIDTH=200 HEIGHT=52 SRC="FIGDIR/small/660106v1_ufig1.gif" ALT="Figure 1"> View larger version (11K): org.highwire.dtl.DTLVardef@1727ccorg.highwire.dtl.DTLVardef@35cb5borg.highwire.dtl.DTLVardef@1b9db10org.highwire.dtl.DTLVardef@dd1f4d_HPS_FORMAT_FIGEXP M_FIG C_FIG