Ecological and social determinants of spacing behaviour in desert baboon groups

This paper investigates the determinants of individual spacing behaviour in a desert baboon population (Papio cynocephalus ursinus). Patterns of neighbour proximity and neighbour density were examined among adults in four groups under different ecological and social conditions (through instantaneous sampling during focal follows). Initial analysis of these data shows that (1) the use of vertical substrates (refuges such as tall trees and cliff faces) can confound patterns of spacing, and (2) individual differences in spacing can depend on the spatial scale over which it is measured. To minimise these substrate and scale effects, this analysis focuses on animals which are off refuges and examines spacing behaviour through its underlying statistical `dimensions' (identified through factor analysis). Analysis of these dimensions indicates that sex, group size, activity-habitat and female reproductive state can all have independent effects on spacing: (1) males are more dispersed than females in smaller groups, (2) male and female dispersion increases with time spent in foraging habitats, and (3) female dispersion is reduced during lactation. According to the hypotheses tested, these results indicate that feeding competition only affects spacing behaviour during foraging while predation risk plays little or no role in spacing. Most aspects of spacing behaviour are best explained by male reproductive strategies and their social repercussions. Received: 25 May 1998 / Accepted after revision: 18 July 1998     

Invading together: the benefits of coalition dispersal in a cooperative bird

Dispersal attempts can be costly and may often end in failure. Individuals should therefore only disperse when the benefits of dispersal outweigh the costs. While previous research has focussed on aspects of the individual that may affect dispersal success, social factors may also influence dispersal outcomes. One way of achieving successful dispersal could be through cooperative, or coalition dispersal. I investigated this possibility in the cooperatively breeding Arabian babbler Turdoides squamiceps. I found that coalition dispersal appears to be an effective strategy to ensure the success of dispersal attempts, with coalitions more successful than lone individuals at taking over the breeding position in a new group. Lone dispersal was more costly than coalition dispersal, with lone individuals suffering a greater loss of body mass during dispersal attempts. These results suggest a substantial short-term benefit for this type of cooperative behaviour. There was no evidence for dispersal polymorphism in the population, with no detectable phenotypic difference between dispersers and non-dispersers or those that dispersed as part of a coalition compared with those that dispersed alone.     

Sociogenetic structure in a free-living nocturnal primate population: sex-specific differences in the grey mouse lemur (Microcebus murinus)

The grey mouse lemur (Microcebus murinus) has a dispersed social structure, within which female sleeping associations are common. These sleeping associations have been hypothesised to confer anti-predatory and thermoregulatory benefits, especially when rearing offspring. The genetic composition of these associations was determined using microsatellite markers to test predictions derived from kin selection theory. 161 (99 males, 62 females) individual M. murinus belonging to a free-living population in Ampijoroa, north-western Madagascar, were genotyped and observed over a total of 13 months distributed over the dry seasons of 3 successive years (1995-1997). Kin selection theory predicts that these female associations should consist of closely related members, and that female philopatry and male natal dispersal should characterise the dispersal pattern within this species. These predictions were confirmed by the data. Five out of six female sleeping groups consisted of one or more closely related dyads. Females that slept alone did not have close female kin in the vicinity or within the population at all. Closely related female dyads lived in significantly closer proximity than closely related male dyads and closely related male-female dyads showed intermediate proximity. In combination with the result that females possessed significantly more relatives within the population than males, these findings support the behavioural hypotheses of female philopatry and male natal dispersal. Matrilinear grouping patterns and sex-biased dispersal are therefore genetically established in a dispersed primate social organisation for the first time. The results further indicate that several generations of mouse lemurs live together within a given area, implying both an effective mechanism of kin recognition to avoid father-daughter incest and the potential for social learning to ensure individual recognition.     

There is a limbo under the moon: what social interactions tell us about the floaters’ underworld

The ultimate and proximate causes of natal dispersal have been extensively investigated, but the behaviour of dispersers in relation to social interactions has been largely neglected. Here, we investigated the social organisation of floating individuals during their dispersal by analysing the behaviour of 40 radio-tagged eagle owls Bubo bubo during the wandering and stop phases of dispersal. Unexpectedly, eagle owl floaters mixed with conspecifics independently of their sex, age, phase of dispersal, birthplace, health status and habitat features, showing an ‘underworld’ of interactions characterised by the absence of obvious social organisation or short-term strategies. Non-breeding owls were not transient floaters that occurred at numerous sites for short periods of time but rather had fairly stable home ranges: they attempted to settle as soon as possible within well-defined home ranges. The spatial distribution pattern of floaters and high rates of home range overlap support the prediction that floating individuals are not spatially segregated, challenging the expectation that dominance by size, age and/or health status may determine the exclusive use of some portions of the dispersal area. Finally, (1) the short distances among conspecifics and the extensive home range overlaps allowed us to discard the possibility that neighbouring floaters represent a real cost during dispersal and (2) floater interactions showed a lack of clear mechanisms for avoidance of kin competition among offspring or inbreeding.     

A dusk chorus effect in a nocturnal bird: support for mate and rival assessment functions

The dawn chorus is a striking feature of spring mornings and a characteristic behaviour of many bird species, particularly the passerines. Dawn singing has been considered a reliable signal of male quality for mate and rival assessment. Singing is presumed to be relatively costly at dawn both because air temperatures are relatively low and because birds have not fed overnight. Models of optimal daily routine predict the existence of a “dusk chorus” in nocturnal birds, although this prediction has received little empirical attention. Nocturnal birds at dusk may be energy-limited because of a lack of daytime feeding, and singing at dusk may thus ensure signal reliability. Here, we used an observational and experimental approach to study vocal behaviour at dusk and dawn in a nocturnal raptor, the little owl Athene noctua. We assess whether male little owls adjust their vocal behaviour according to feeding stage (i.e. period of the night), ambient air temperature and territorial context (i.e. spontaneous calling behaviour vs elicited calling by intrusion). Across different temperatures, we find that both spontaneous vocal activity and inter-individual variability in call duration increased at dusk, clearly indicating a dusk chorus phenomenon. Results from playback presentations suggest that food, rather than air temperature, is likely to be more constraining at dusk. We discuss how comparing dusk and dawn choruses in nocturnal and diurnal species can provide insights into both mechanistic and functional aspects of signalling behaviour.     

Seasonal variation in the duetting behaviour of rufous-and-white wrens (<Emphasis Type="Italic">Thryothorus rufalbus</Emphasis>)

Seasonal variation in animal signalling behaviour has been well documented and has contributed much to our understanding of male signals. In contrast, we know little about seasonal variation in female signals or signals produced jointly by males and females, such as the vocal duets of birds. Here, we examine how singing behaviour changes in relation to time of year and breeding stage in rufous-and-white wrens (Thryothorus rufalbus), neotropical songbirds where both males and females sing and where breeding partners coordinate songs to produce vocal duets. We recorded a colour-marked population of birds over an extended time period encompassing multiple breeding stages. Across all time frames and breeding stages, males sang at higher rates than females and male solos were more common than duets or female solos. Males and females showed divergent seasonal patterns of singing. Females sang more often early in the year, during the pre-breeding season, and female song tapered off as the breeding season progressed. Duetting followed a parallel pattern, which resulted from females showing less duet responsiveness to their partner’s songs later in the year. Male independent song rate peaked at the onset of the rainy season – a time when females become fertile – and males showed the highest level of duet responsiveness during this period. Our results suggest that early in the year, duets appear to be cooperative displays, functioning in joint territory defence and/or the coordination of breeding activities. When females are fertile, however, increased duet responsiveness by males is consistent with mate or paternity guarding.     

Vocal interactions in common nightingales (<Emphasis Type="Italic">Luscinia megarhynchos</Emphasis>): males take it easy after pairing

Seasonal patterns of bird song have been studied intensively with a focus on individual males. However, little is known about seasonal patterns of singing during vocal interactions between males. Vocal interactions have been shown to be important in sexual selection as males may signal aspects of motivation or quality. Here, we investigated in nightingales (Luscinia megarhynchos) whether a male’s behaviour in vocal interactions at different stages of the breeding season is influenced by its mating status. We examined how males that differ in their subsequent mating success respond to a non-interactive, nocturnal playback presented during the period of mate attraction and subsequently during the egg-laying period. We found that mated males overlapped fewer songs and had a lower song rate during the egg-laying period compared to their responses during the mate-attraction period, whereas unpaired males did not vary in their responses between the two periods. Our results suggest that mating status is a key factor affecting singing behaviour in vocal interactions and that a time-specific singing pattern like song overlapping is used flexibly during vocal interactions. Because song overlapping is thought to be a signal of aggression in male–male vocal interactions, it seems that males vary the level of aggression in vocal interactions according to their mating status and to the stage in the breeding season.     

Females go where the food is: does the socio-ecological model explain variation in social organisation of solitary foragers?

The socio-ecological model (SEM) links ecological factors with characteristics of social systems and allows predictions about the relationships between resource distribution, type of competition and social organisation. It has been mainly applied to group-living species but ought to explain variation in social organisation of solitary species as well. The aim of this study was to test basic predictions of the SEM in two solitary primates, which differ in two characteristics of female association patterns: (1) spatial ranging and (2) sleeping associations. Beginning in August 2002, we regularly (re-)captured and marked individuals of sympatric populations of Madame Berthe's and grey mouse lemurs (Microcebus berthae, Microcebus murinus) in Kirindy Forest (Madagascar). We recorded data on spatial patterns, feeding and social behaviour by means of direct observation of radio-collared females. The major food sources of M. berthae occurred in small dispersed patches leading to strong within-group scramble competition and over-dispersed females with a low potential for female associations. In contrast, M. murinus additionally used patchily distributed, high-quality (large) resources facilitating within-group contest competition. The combined influence of less strong within-group scramble and contest as well as between-group contest over non-food resources allowed females of this species to cluster in space. Additionally, we experimentally manipulated the spatial distribution of food sources and found that females adjusted their spatial patterns to food resource distribution. Thus, our results support basic predictions of the SEM and demonstrated that it can also explain variation in social organisation of solitary foragers.     

Macro-habitat patch structure,environmental harshness,and Marmota flaviventris

Summary Social behavior of 15 colonies of Yellow-bellied Marmots was studied at sites differing in both elevation (plant growing season length) and patch structure (density and spacing of suitable colony sites in large blocks of habitat) from 1976 through 1978. Colonies were typically composed of family groups. In low elevation colonies, offspring dispersed at the end of the juvenile year. In all high elevation areas, offspring dispersed as yearlings, and parent-offspring and sibling interactions during the juvenile year were highly amicable. In high elevation areas in continuous habitat, dispersal by yearlings occurred with no agonistic interactions. In high elevation areas with patchy habitat, however, brief but intense periods of extremely agonistic sibling and parent-offspring interactions occurred immediately prior to dispersal of yearlings.Social behavior and dispersal are uncorrelated with elevation, plant growing season length, or available foraging time. Social interaction among relatives in marmot colonies is amicable when other suitable colony sites are located nearby; in these areas, dispersal occurs without any antagonism. Agonistic behavior occurs only in areas with a patchy distribution of suitable colony sites. At these sites, dispersal occurs only after periods of extreme antagonism. Further, those offspring who do not disperse from the colony site are the ones who dominate and initiate agonistic interactions with their siblings. The large-scale structure of the habitat influences the propensity of the individual to disperse. When the animal is reluctant to disperse because of a combination of high transit difficulty and low desirability of a new site, angonistic social interactions with relatives force dispersal.     

Dispersal behaviour in a subsocial spider: group conflict and the effect of food availability

This study investigates proximate factors influencing dispersal behaviour in the subsocial spider Amaurobius ferox. Dispersal of spiderlings from the natal web occurred as a progressive sigmoidal function (mean duration of dispersal period=31 days), with considerable individual variability in developmental instar and body mass within the clutch at the time of dispersal. The spiderlings showed a significant decrease in group cohesion on the 6th day after their second moult, which corresponded to the beginning of the dispersal period. Mutual aggressiveness appeared when the spiderlings began to show predatory behaviour (4th day post-second moult) and increased over the course of the dispersal period. While lack of prey in the maternal nest accelerated dispersal behaviour, the addition of prey items lengthened the dispersal period in previously non-fed clutches. Individuals that dispersed were smaller than the remaining individuals when measured on the day 50% of the clutch had dispersed. Timing of the appearance of the developmental characters (second moult, predation activity, agonistic behaviour against siblings, reduction of group cohesion, dispersal) suggests that the dispersal trait might have evolved in consequence of these different functional behaviours. Received: 10 August 1999 / Received in revised form: 15 March 2000 / Accepted: 1 April 2000     

Loud calls as a mechanism of social coordination in a fission–fusion taxon, the white-bellied spider monkey (Ateles belzebuth)

Spider monkeys (Ateles spp.) live in social groups that exhibit high levels of fission–fusion dynamics, in which group members form subgroups of varying sizes and compositions. Within these fluid societies, how individuals establish contact with dispersed group members with whom they might choose to associate remains unclear. Long-range vocalizations might facilitate interactions between group members and provide a means of social coordination in fission–fusion societies. We evaluated this possibility for one spider monkey vocalization, the loud call, by examining calling behavior, the relationship between loud calls and changes in subgroup size, and the response of individuals to distant calls and playback experiments in a single study group. We found that 82 % of loud calls were emitted within 30 min of a call from a different location, suggesting that individuals frequently emit loud calls in response to the calls of distant group members. Subgroups that emitted loud calls, especially those that responded to distant calls, were much more likely to experience an increase in subgroup size within an hour after calling than those that did not. Animals also approached distant loud calls more than they avoided or ignored these calls. Finally, playbacks of male calls demonstrated that females respond preferentially to the calls of some individuals over others. Taken together, these results provide support for the hypothesis that spider monkey loud calls function to facilitate and initiate interactions between dispersed group members and suggest that vocal signals can play an important role in influencing social interactions in fission–fusion societies.     

Early learning of discrete call variants in red crossbills: implications for reliable signaling

The identification of appropriate companions and mates is essential to both speciation and the maintenance of species through prezygotic isolation. In many birds, social assortment is mediated by vocalizations learned through imitation. When imitative vocal learning occurs throughout life, emergent shared signals reflect current social associations. However, when vocal and genetic variation arises among populations, shared learned signal variants have a potential to reflect cultural or genetic origin and to limit social and reproductive intermixing, provided that signal learning occurs prior to dispersal. The red crossbill (Loxia curvirostra) is a bird species in which discrete contact call variants are associated with morphological variation, raising the possibility that learned calls play a role in limiting intermixing. I examined the process of early call learning to determine if contact call variants have a potential to limit intermixing in crossbills. I conducted a captive playback study to nestlings to evaluate potential learning predispositions. I also cross-fostered nestlings to adoptive adult pairs of either their own or a different call variant than their biological parents to assess the degree of vocal learning plasticity. Results show that young crossbills imitate the call structures of adoptive parents, generating shared family-specific calls, which could facilitate family cohesion. Learning processes that generate family-specific calls could also ensure that discrete call variants are transmitted across generations, making call variants reliable signals of crossbills’ morphological and genetic backgrounds.     

Incorporating animal behavior into seed dispersal models: implications for seed shadows

Seed dispersal fundamentally influences plant population and community dynamics but is difficult to quantify directly. Consequently, models are frequently used to describe the seed shadow (the seed deposition pattern of a plant population). For vertebrate-dispersed plants, animal behavior is known to influence seed shadows but is poorly integrated in seed dispersal models. Here, we illustrate a modeling approach that incorporates animal behavior and develop a stochastic, spatially explicit simulation model that predicts the seed shadow for a primate-dispersed tree species (Virola calophylla, Myristicaceae) at the forest stand scale. The model was parameterized from field-collected data on fruit production and seed dispersal, behaviors and movement patterns of the key disperser, the spider monkey (Ateles paniscus), densities of dispersed and non-dispersed seeds, and direct estimates of seed dispersal distances. Our model demonstrated that the spatial scale of dispersal for this V. calophylla population was large, as spider monkeys routinely dispersed seeds >100 m, a commonly used threshold for long-distance dispersal. The simulated seed shadow was heterogeneous, with high spatial variance in seed density resulting largely from behaviors and movement patterns of spider monkeys that aggregated seeds (dispersal at their sleeping sites) and that scattered seeds (dispersal during diurnal foraging and resting). The single-distribution dispersal kernels frequently used to model dispersal substantially underestimated this variance and poorly fit the simulated seed-dispersal curve, primarily because of its multimodality, and a mixture distribution always fit the simulated dispersal curve better. Both seed shadow heterogeneity and dispersal curve multimodality arose directly from these different dispersal processes generated by spider monkeys. Compared to models that did not account for disperser behavior, our modeling approach improved prediction of the seed shadow of this V. calophylla population. An important function of seed dispersal models is to use the seed shadows they predict to estimate components of plant demography, particularly seedling population dynamics and distributions. Our model demonstrated that improved seed shadow prediction for animal-dispersed plants can be accomplished by incorporating spatially explicit information on disperser behavior and movements, using scales large enough to capture routine long-distance dispersal, and using dispersal kernels, such as mixture distributions, that account for spatially aggregated dispersal.     

Caribbean mangroves and seagrass beds as daytime feeding habitats for juvenile French grunts, Haemulon flavolineatum

Caribbean seagrass beds are important feeding habitats for so-called nocturnally active zoobenthivorous fish, but the extent to which these fishes use mangroves and seagrass beds as feeding habitats during daytime remains unclear. We hypothesised three feeding strategies: (1) fishes feed opportunistically in mangroves or seagrass beds throughout the day and feed predominantly in seagrass beds during night-time; (2) fishes start feeding in mangroves or seagrass beds during daytime just prior to nocturnal feeding in seagrass beds; (3) after nocturnal feeding in seagrass beds, fishes complete feeding in mangroves or seagrass beds during the morning. We studied the effect of habitat type, fish size, social mode and time of day on resting and feeding behaviour of large juvenile (5–10 cm) and sub-adult (10–15 cm) Haemulon flavolineatum in mangroves and seagrass beds during daytime. Sub-adults occurred in mangroves only, spent most time on resting, and showed rare opportunistic feeding events (concordant with strategy 1), regardless of their social mode (solitary or schooling). In contrast, large juveniles were present in both habitat types and solitary fishes mainly foraged, while schooling fishes mainly rested. Exceptions were small juveniles (±5 cm) in seagrass beds which foraged intensively while schooling. Large juveniles showed more feeding activity in seagrass beds than in mangroves. In both habitat types, they showed benthic feeding, whereas pelagic feeding was observed almost exclusively in the seagrass beds. In both habitat types, their feeding activity was highest during 8:00–10:30 hours (concordant with strategy 3), and for seagrass fishes, it was also high during 17:30–18:30 hours (concordant with strategy 2). The study shows that both mangroves and seagrass beds provide daytime feeding habitats for some life-stages of H. flavolineatum, which is generally considered a nocturnal feeder.     

Sex-biased dispersal in a long-lived polygynous reptile (Crocodylus johnstoni )

We compared natal dispersals of freshwater crocodiles (Crocodylus johnstoni) against the prediction of male dispersal bias for a polygynous mating system. The crocodiles inhabited a linear series of pools and we calculated the net distances from natal pools to recapture locations some 12–18 years later, at maturity. Philopatry was assessed in terms of adult social distances. A female social distance was 0.46 pools and a male social distance was 1.0 pool. By these criteria, both sexes showed low levels of philopatry (7–12%). However, individuals of both sexes dispersed from the natal site long before they were sexually mature. Divergence in dispersal patterns by sex occurred after the maturity threshold, as males dispersed two to three times farther than females. Intrasexual competition by males is resolved by a size-based hierarchy. The displacement of small males from local mating access is a probable cause of the longer dispersals undertaken by males. Competition, rather than inbreeding avoidance, is driving dispersal in this population of freshwater crocodiles. Received: 8 May 1998 / Accepted after revision: 26 June 1998     

Neighborhood effects on seed dispersal by frugivores: testing theory with a mistletoe-marsupial system in Patagonia

The outcome of the dispersal process in zoochorous plants is largely determined by the behavior of frugivorous animals. Recent simulation studies have found that fruit removal rates and mean dispersal distances are strongly affected by fruiting plant neighborhoods. We empirically tested the effects of conspecific fruiting plant neighborhoods, crop sizes, and plant accessibility on fruit removal rates and seed dispersal distances of a mistletoe species exclusively dispersed by an arboreal marsupial in Northern Patagonia. Moreover, in this study, we overcome technical limitations in the empirical estimation of seed dispersal by using a novel 15N stable isotope enrichment technique together with Bayesian mixing models that allowed us to identify dispersed seeds from focal plants without the need of extensive genotyping. We found that, as predicted by theory, plants in denser neighborhoods had greater fruit removal and shorter mean dispersal distances than more isolated plants. Furthermore, the probability of dispersing seeds farther away decreased with neighborhood density. Larger crop sizes resulted in larger fruit removal rates and smaller probabilities of longer distance dispersal. The interplay between frugivore behavioral decisions and the spatial distribution of plants could have important consequences for plant spatial dynamics.     

Temporal performance roles during vocal interactions in nightingales (Luscinia megarhynchos B.)

Summary The temporal patterning of vocal interactions between territorial nightingales (Luscinia megarhynchos B). was investigated during nocturnal dyadic singing. We distinguished three forms of temporal performance roles (Table 1; Fig. 3): inserter (preferred song start 0.5–1.0 s after offset of a neighbour's song), overlapper (preferred song start 0.5–1.0 s after onset of a neighbour's song), and Autonomous bird (no evidence for temporal responses adjusted to the timing of a neighbour's singing; Fig. 4). With the beginning of the daily dawn chorus, mutual temporal adjustment of song performances could no longer be ascertained (Fig. 2). To test the flexibility of song onset timing, we presented subjects with three playback programs (I, II, III) simulating a non-flexible conspecific bird. Sequences of songs recorded from a stranger that shared no song types with the subjects were used; intersong pauses were unaltered in I, lengtened in II, and shortened in III. Results confirmed that the timing of song onset can be influenced by the temporal patterning of auditory stimuli (Table 1; Fig. 5): Inserters and overlappers sang at a slower rate during program II than during program I. During program III, which by accelerated stimulus succession caused frequent overlap of songs, inserters and overlappers interrupted their singing behaviour (Fig. 6). This suggests that overlapping, which results in signal interference, is of some functional significance in vocal interactions.     

To whom it may concern: the transmission and function of chemical signals in Lemur catta

The goals of this study were to investigate the transmission and possible functions of chemical signals in intragroup communication among ring-tailed lemurs, Lemur catta. In particular, I examined the effects of sex on these processes because sexual selection theory predicts specific functions for chemical signals. I recorded all interactions with 214 scent marks of 11 male and 9 female ring-tailed lemurs during the first 10 min following their deposition. I found that 62% of these scent marks were investigated with a median latency of 30 s and that 89% of investigated scents were also counter-marked by the receiver. The type of focal scent mark (male or female anogenital and male antebrachial mark) had a significant effect on both the timing and type of response. Males investigated and counter-marked female scents more often than vice versa, but significant second-order transitions suggested that the behavior of an animal was not only influenced by the immediately preceding scent mark and that a scent is not completely masked by a counter-mark. There was no evidence for an audience effect, and only social rank of female senders had an effect on receivers. Variation in the response of receivers across reproductive seasons as a function of senders' sex indicated that female scents may function in mate attraction and competition among females, whereas male scents may be primarily used in intrasexual competition. Three main conclusions emerged. First, the exchange of olfactory signals within groups was highly structured and surprisingly efficient. Second, olfactory signals may constitute general mesasages whose transfer is partly controlled by the receiver. Finally, sexual selection theory provides a useful theoretical framework for functional examinations of mammalian olfactory communication. Received: 13 June 1997 / Accepted after revision: 20 March 1998     

Bachelor and paired male rufous-and-white wrens use different singing strategies

To attract a breeding partner, males may behave differently when they are bachelors compared to when they are paired. Comparisons between groups of paired males versus groups of unpaired males in temperate-breeding animals have revealed such differences in signalling behaviour. Few studies, however, have explored how individual males alter their signalling behaviour with changes in pairing status, and very few investigations have explored paired versus unpaired male behaviour in tropical animals. During a 5-year study in Costa Rica, we analysed changes in the singing behaviour of male rufous-and-white wrens (Thryothorus rufalbus) when they were paired and when they were bachelors. We compared three aspects of male vocal behaviour: gross differences in song output, variation in repertoire use and differences in song structure. Males as bachelors had significantly higher song output and switched song types less frequently. Contrary to our expectation, bachelors sang significantly fewer song types from their repertoire compared to when those same males had a breeding partner. Songs sung by bachelor males were higher in syllabic diversity and had broader-bandwidth terminal syllables than the songs those males sang only when paired. Within song types, the fine structure of songs remained consistent across pairing status. Our results demonstrate that males change their singing behaviour with pairing status, delivering songs at a higher rate but with less variety when they are bachelors. Rufous-and-white wrens are renowned for their vocal duets, and we discuss the pattern of repertoire use in light of their duetting behaviour. These results enhance our understanding of how male behaviour varies with pairing status and the importance of vocal signalling behaviour in socially monogamous tropical animals.