Leader Males Research Articles

Migration of a harem in search of a new leader following the loss of the former adult male leader from a one-male unit of geladas (Theropithecus gelada).

Geladas (Theropithecus gelada) live in social groups consisting of one-male units (sometimes referred to as "harems"), bands, and all-male units. Takeover by a new male affects the reproductive success and mating strategies of the individuals in a harem. However, to the best of my knowledge, there is no information available on the fate of the females in a one-male unit whose leader dies or disappears and is not replaced by another adult male. In 2017, I observed the migration of a male-less unit into the home range of my study group at Kosheme, in Wollo, Ethiopia. The unit consisted of 14 individuals. I observed the harem leader of my study group desert his unit and join the new unit, which appeared to peacefully accept him as their leader. These observations are in agreement with information from local residents, who told me that if the leader male of a unit dies, the male-less group (the "survivors") will soon migrate in search of a new adult male leader. To the best of my knowledge, this is the first documented case of the migration of a gelada harem in search of an adult male leader after the loss of the unit's former leader. This report contributes toward a better understanding of the reproductive behavior of geladas in particular, and of primates in general.

Social and paternal female choice for male MHC genes in golden snub-nosed monkeys (Rhinopithecus roxellana).

Genes of the major histocompatibility complex (MHC) play important roles in vertebrate immunocompetence. MHC genes thus offer females indirect benefits to mate choice through the production of offspring of an optimal MHC genotype. Females may choose males with specific MHC haplotypes, dissimilar MHC genotypes, MHC heterozygous males or MHC-diverse males. We tested these four alternatives for both female social and paternal choice in wild golden snub-nosed monkeys (Rhinopithecus roxellana) by examining overall genetic variability (via microsatellites) and four MHC-genes (DRB1, DRB2, DQA1 and DQB1). Monte Carlo randomization tests showed that MHC dissimilarity was favoured for social choice (males to which females were socially affiliated) and intermediate MHC dissimilarity was favoured in paternal choice (fathers of offspring). No evidence of inbreeding avoidance was found for either social or paternal mates. We found that MHC heterozygotes, higher microsatellite multilocus heterozygosity and higher microsatellites diversity were favoured for social mates, and higher microsatellite diversity was favoured for paternal mates. Independent of male age, we found that the formation of male-female social pairings is significantly predicted by compatibility based on the sharing of MHC haplotypes. However, we found no evidence of independent genetic effects on the duration of male-female social pairings, male social status (achieving OMU leader male status or not), the number of females with which individual leader males paired, the likelihood of potential male-female pairings producing offspring, or whether males fathered offspring or not. Overall, our findings suggest different genetic factors are involved in social and paternal choice in R. roxellana.

Respect for males amid suppression of females: Selective use of aggression and fitness correlates in the male-dominated society of hamadryas baboons

Hamadryas baboons (Papio hamadryas) are a useful model for human social evolution for multiple reasons, including their multilevel society, intense cross-sex bonds, and intermale tolerance. Their most stable social grouping, the one-male unit (OMU)—comprising a leader male, females, and sometimes follower males—is formed via successive takeovers of individual females by males. While takeovers occur via both aggressive and non-aggressive mechanisms, aggressive herding is common during and after takeovers and appears crucial in maintaining OMUs. Here we use behavioral and demographic data from Filoha, Ethiopia to examine the relationship between aggressive takeovers and fitness correlates. We found no relationship between a male's percentage of takeovers that were aggressive and his presumed number of infants sired, nor his number of females or followers. However, we did find that a leader male's average intensity of aggression toward both other males and females around the time of a takeover was negatively related to his presumed number of infants sired. In addition, a leader male's average intensity of aggression toward other males was negatively related to his maximum number of followers. Finally, leader males exhibited more intense aggression toward females in interband, compared to intraband, takeovers. Our findings suggest that (1) leader males who limit their aggression toward other males may have greater success in attracting followers, thereby increasing their fitness via enhanced defense of the OMU; (2) exceptionally aggressive takeovers may lead to lower birth rates via female reproductive suppression; and (3) the extent to which males use aggression toward females depends on the context in which the takeover occurs. Overall, these results both suggest that hamadryas males use aggression selectively and underscore the ubiquity of intermale tolerance and female suppression in the hamadryas social system. This study lends insight into the interplay between male–female and male–male social dynamics during human evolution.

Male and female birth attendance and assistance in a species of non-human primate (Rhinopithecus bieti)

Birth attendance, or midwifery service, is an important characteristic in human evolution, and has been argued to separate our lineage from other taxa in the animal kingdom. Recent studies, however, indicate that similar or analogous behaviors also may occur in a small number of nonhuman primate species. Here, we report the first case of both male and female attendance and female birth assistance in a wild species of nonhuman primate, the black-and-white snub-nosed monkey (Rhinopithecus bieti). At our field site in Yunnan, China we observed a diurnal birth event in which the leader male of a one-male unit (OMU) remained in close- proximity (0–2 m) to the parturient, groomed her, and remained vigilant over a five hour pre- and postpartum period. In addition, a multiparous female member of the OMU also remained in close proximity to the soon-to-be mother, helped to pull the neonate from the birth canal, took the neonate from the new mother within 15 s of the birth, held the infant for 20 min, and then severed the umbilical cord. For the next several days the leader male traveled in close-proximity to the new mother and four days after the birth event, we observed him to share food with her. Given that diurnal births are extremely rare in this primate species; it remains unclear the degree to which the events we observed commonly occur during nighttime births. We argue that adult male and female black-and-white snub-nosed monkeys are highly attracted to young infants, and birth attendance and birth assistance in this, and certain other primate species, may play a critical role in maternal and infant survivorship.

Multilevel societies facilitate infanticide avoidance through increased extrapair matings

In mammals characterized by a mating system in which a single male monopolizes reproduction, infanticide is reported to occur following a male take-over, often resulting in females returning to oestrus more rapidly than if their infant has survived. However, over the course of a 17-year study of golden snub-nosed monkeys, Rhinopithecus roxellana, a polygynous colobine species, we found no behavioural or suspected evidence of infanticide. Based on social network and genetic analyses, we found that more than half of the infants were sired as a result of extrapair matings (EPMs). Female golden snub-nosed monkeys initiated EPMs with bachelor or neighbouring resident males. These were considered ‘sneaky’ copulations because they did not occur in the presence of the leader male of the female's one-male unit (OMU). We suggest that through a process of paternity confusion, females decreased the likelihood of infanticide after a male take-over. In contrast, in a group of the same species in which the number of bachelor males was artificially reduced, EPMs were infrequent and four cases of infanticide were observed, three of them following a male take-over. Golden snub-nosed monkeys reside in a large multilevel society that develops by the fusion of several independent OMUs to form a breeding band, which is characterized by increased social cohesion and intrasexual tolerance among leader males. Females play an active role in mate choice, and engage in a diverse set of mating tactics, including counterstrategies such as EPMs to avoid infanticide. These results offer new insights into the diversity of behavioural strategies facilitated by complex social structures in nonhuman primates, as well as other social mammals.

Lengthy leader male tenure delays male offspring dispersal in a primate multilevel society

Abstract Natal dispersals are male-biased in most Old World monkey species, especially those that are polygynous. We examined patterns of male dispersal in golden snub-nosed monkeys, in which male offspring mainly disperse as juveniles from their natal one-male units (OMUs) to a bachelor group. However, out of a total of 112 male dispersals from 2001–2016, we documented six cases in which male offspring remained in their natal OMU until sub-adulthood. Based on monitoring of dispersal dynamics, we found that male offspring were more likely to delay dispersal if the tenure of leader males was lengthy. Social network analysis showed male offspring who delayed dispersal exhibited strong social relationships with each other and their OMU leader male but not with the females of their OMU. Our results suggest that the length of leader male tenure may affect natal male dispersal due to benefits to leader males accrued via intrasexual competition and kin selection.

Seasonal changes in social cohesion among males in a same-sex primate group.

Male-male interactions in mixed-sex groups of social mammals are typically characterized by a mix of hostility and affiliation, as a result of inherent conflicts over mating opportunities, and the costs and benefits of social alliances, co-operative behaviors, and coalitionary defense. In species of nonhuman primates that form all-male groups, it is still unclear how the tradeoffs between the benefits of forming an all-male group and the cost of male-male competition in seeking mating opportunities with females in bisexual groups influence social cohesion in different seasons. Here, we used social network analysis to quantify the impact of reproductive seasonality on social cohesion and clique size of bachelor males residing in an all-male unit (AMU) in wild black-and-white snub-nosed monkeys (Rhinopithecus bieti). These primates are strict seasonal breeders and live in a modular social system composed of a number of one-male units (OMUs) and an associated peripheral AMU. We found that the AMU social network had a significantly lower density, centralization, clustering coefficient, and smaller clique size during the mating season compared to the non-mating period. However, aggression among AMU males during both mating and non-mating periods was low. Our results suggest that network structure topology in male same-sex social units is modulated by seasonal changes. Bachelor males engage in two types of competition to gain reproductive success: first, which is analogous to contest competition, in which bachelor males act aggressively and challenge OMU leader males in an attempt to take over an OMU; and second, which is more analogous to scramble competition, in which bachelor males avoid aggressive interactions and instead engage in sneaky copulations with fertile females. Our work adds to an understanding of the maintenance of all-male groups in species that form a multilevel society.

Evidence for mutual assessment in a wild primate

In aggressive interactions, game theory predicts that animals should assess an opponent’s condition relative to their own prior to escalation or retreat. Despite the benefits of such mutual assessment, few studies have been able to reject simpler assessment strategies. Here we report evidence for mutual assessment in a wild primate. Gelada (Theropithecus gelada) males have conspicuous loud calls that may function as a signal of male quality. “Leader” males with harems putatively use loud calls to deter challenges from non-reproductive “bachelor” males. By contrast, leader males pose no threat to each other and congregate in large groups for a dilution effect against bachelors. In playback experiments and natural observations, gelada males responded to loud calls according to both their own and their opponent’s attributes. Although primates routinely classify others relative to themselves using individual attributes, this represents some of the first direct evidence for mutual assessment in primate signaling contests.

Male Infanticide in the Golden Snub-Nosed Monkey (Rhinopithecus roxellana), a Seasonally Breeding Primate

In nonhuman primates, infanticide by adult males can occur when the leader male is ousted from a one-male, multifemale group, or when male dominance rank changes within a multimale, multifemale group. According to the sexual selection hypothesis, this behavior may be adaptive if perpetrators increase their reproductive success by killing unrelated, unweaned infants, thus shortening the interbirth interval of the mother, and then siring her next infant. Under an alternative hypothesis, infanticide is a byproduct of aggressive male–male competition and these predictions do not hold. Direct observations of the context surrounding infanticide in free-ranging primate populations that allow a test of these predictions are rare. Here, we document four cases of male infanticide and report paternity data for a group of golden snub-nosed monkeys (Rhinopithecus roxellana) at Shennongjia, China. Three cases of infanticide by new leader males supported the predictions of the sexual selection hypothesis, while another provides partial support for the sexual selection hypothesis, but can also be explained via a nonadaptive hypothesis. In this latter case, a male from an all-male group killed an infant during an aggressive episode that appeared to be accidental, as it took place 7 mo before a male takeover happened, and the perpetrator did not obtain any reproductive advantage. We conclude that most male infanticide events in golden snub-nosed monkeys are consistent with the adaptive selection sexual hypothesis.

Postconflict behavior among Rhinopithecus roxellana leader males in the Qinling Mountains, China.

Since reconciliation was first described more than 20 years ago, a large number of postconflict behaviors have been observed among females in many polygynous primate species. However, few studies have been conducted among males, perhaps due to the rarity with which they maintain friendly relationships with one another and their aggressive competition for resources. Although this is true for many primate males, Sichuan snub-nosed monkeys Rhinopithecus roxellana represent a potential exception as male cooperation has been known to occur. In this study, using postconflict/matched-control(PC–MC) and time-rule methods, we analyzed postconflict behavior among males and the possible occurrence of bystander affiliation or reconciliation. A total of 246 PC–MC pairs among leader males were obtained. On average, each leader male exhibited only 0.04 aggressive behaviors per observation hour, and conciliation among leader males occurred at a low rate (2.03%) relative to other primate species. The occurrence of consolation–affiliation interactions between focal males and group members other than former opponents differed significantly between PCs and MCs, which is the first time this has been confirmed among R. roxellana males. We discuss the results in light of recent theories concerning consolation in primates. The patterns of postconflict contact demonstrated that R. roxellana may be a unique species among colobines.

The adaptive value of secondary males in the polygynous multi-level society of hamadryas baboons.

One-male social systems are usually characterized by polygyny and reproductive exclusion by a single resident male. Sometimes, however, secondary males join these groups, and this may carry fitness costs and/or benefits to the resident male. In hamadryas baboons (Papio hamadryas hamadryas), which live in one-male units (OMUs) with female defense polygyny within a multi-level social system, secondary "follower" males often reside in OMUs. Our aim here is to examine possible benefits of these secondary males to hamadryas resident males. Using 6 years of data from 65 OMUs in a band of wild hamadryas baboons in Ethiopia, we compared demographic and reproductive parameters of OMUs with and without secondary "follower" males to assess whether their presence conferred any reproductive benefits to resident "leader" males. Leaders with followers had tenure lengths almost twice as long, acquired more than twice as many females, retained females longer, and had three times as many infants during their tenure compared to leaders without followers. Hamadryas follower males enabled leaders to retain females for longer periods of time-likely through unit defense, social relationships with OMU members, and/or infant protection. Hamadryas leaders appear to be able to monopolize access to females despite the presence of followers, and as such any enhanced reproduction derived from the presence of followers likely increases the fitness of the leader rather than the follower. Thus the relationship between leaders and followers in hamadryas society appears to be a mutually beneficial one and tolerance of secondary males may be an adaptive reproductive strategy characterizing hamadryas leader males.

The role of kinship in the formation of a primate multilevel society.

A small number of mammalian species live in a modular or multilevel society in which several individual social/reproductive units called one-male units (OMUs) are embedded within a large cohesive band. Factors that affect band composition and stability are poorly understood. In this study we examined the role of kinship in the formation and maintenance of a multilevel society in an endangered population of golden snub-nosed monkeys (Rhinopithecus roxellana). From 2005 to 2011, we obtained genetic samples from 86 individuals (including 88.9% of leader males and 80.5% of adult females) living in a band of 8-10 OMUs. We used microsatellite genotyping to identify patterns of relatedness and individual transfer. We found that adult females residing in the same OMU were more closely related to each other than to a random set of females drawn from the band and that females tended to disperse into OMUs that contained female relatives. In addition, adult females who transferred were not more closely related to their previous leader male than to the leader male of their new OMU. These results support the contention that kin bonds contribute importantly to the formation and stability of this primate multilevel society by influencing a female's decision to remain in her current OMU, or during transfer, which new OMU to enter.

The rise and fall of leader males in a multi-level society: takeovers and tenures of male Hamadryas baboons.

As one means to maximize access to females, males of some species are intolerant of other males in social units, resulting in female defense polygyny, a mating system in which one male monopolizes mating access to as many females as he can for as long as possible. In such a system, the length of a male's tenure and the number of females he is able to acquire are important predictors of his reproductive success. Hamadryas baboons differ from many other taxa with female defense polygyny in that they acquire and lose females individually, thus patterns of acquisition and loss of females over time are additional factors contributing to a male's fitness. Here, we describe longitudinal patterns of female acquisition and loss over a 9-year period in a group of 250 wild hamadryas baboons. Complete tenures of leader males ranged from 310 to 2,160 days (N = 13) and results from a survival analysis yielded a median tenure length of 2,160 days, or 6 years (N = 49). The total number of females acquired, which increased with tenure length, ranged from 1 to 14 and averaged 3.5, and leader males acquired females both opportunistically and via challenging other males. The interval between acquisition of successive females ranged from 0 to 1,196 days with a median of 203, and males acquired all of their females less than halfway into their tenure. Females from outside of a leader male's social sphere (clan and band) were acquired relatively later in their tenure compared to females from within a male's social sphere. Leaders typically lost females gradually during the latter part of their tenure or all (or most) at once, suggesting an inverted U-shaped longitudinal arc of male competitive ability.

Evolution of Multilevel Social Systems in Nonhuman Primates and Humans.

Multilevel (or modular) societies are a distinct type of primate social system whose key features are single-male–multifemale, core units nested within larger social bands. They are not equivalent to fission–fusion societies, with the latter referring to routine variability in associations, either on an individual or subunit level. The purpose of this review is to characterize and operationalize multilevel societies and to outline their putative evolutionary origins. Multilevel societies are prevalent in three primate clades: papionins, Asian colobines, and hominins. For each clade, we portray the most parsimonious phylogenetic pathway leading to a modular system and then review and discuss likely socioecological conditions promoting the establishment and maintenance of these societies. The multilevel system in colobines (most notably Rhinopithecus and Nasalis) has likely evolved as single-male harem systems coalesced, whereas the multilevel system of papionins (Papio hamadryas, Theropithecus gelada) and hominins most likely arose as multimale–multifemale groups split into smaller units. We hypothesize that, although ecological conditions acted as preconditions for the origin of multilevel systems in all three clades, a potentially important catalyst was intraspecific social threat, predominantly bachelor threat in colobines and female coercion/infanticide in papionins and humans. We emphasize that female transfers within bands or genetic relationships among leader males help to maintain modular societies by facilitating interunit tolerance. We still lack a good or even basic understanding of many facets of multilevel sociality. Key remaining questions are how the genetic structure of a multilevel society matches the observed social effort of its members, to what degree cooperation of males of different units is manifest and contributes to band cohesion, and how group coordination, communication, and decision making are achieved. Affiliative and cooperative interunit relations are a hallmark of human societies, and studying the precursors of intergroup pacification in other multilevel primates may provide insights into the evolution of human uniqueness.

Male dispersal in a provisioned multilevel group ofRhinopithecus roxellanain Shennongjia Nature Reserve, China

Most Old World monkeys show male-biased dispersal. We present the first systematic data on male dispersal in a provisioned multilevel group of Rhinopithecus roxellana, based on 4.5 years of field observations in Shennongjia National Nature Reserve, China. We evaluated both ultimate (inbreeding avoidance and male mating competition) and proximate (food availability and predation risk) factors influencing male dispersal. The focal group contained 34-53 individuals, in 3-4 one-male units (OMUs) and 1 all-male unit (AMU). We observed 37 dispersal events involving 10 of 11 adults, 7 of 8 subadults, and 7 of 15 juveniles. Most interunit transfers within the focal group occurred around the months of mating season. Adult males competed for the leader positions of OMUs mainly through aggressive takeovers, and young males transferred from the OMUs to the AMU at the median age of 41 months, forced out by leader males. No young males older than 4 years remained in natal or non-natal OMUs. The male mating competition hypothesis was supported. The young males emigrated voluntarily from the focal group at the average age of 58.6 months, and no young emigrating male was observed to return, suggesting inbreeding avoidance also played a role in the dispersal of young males. Most emigration/immigration events were parallel dispersal and occurred during intergroup encounters, suggesting increased predation risk during the dispersal period. Males were more likely to emigrate/immigrate during the months when preferred foods were most available. We compared the dispersal patterns in R. roxellana with those in gelada baboons and hamadryas baboons, both living in multilevel societies. Similar to R. roxellana, young male geladas disperse at puberty, but they may return and breed in their natal groups. Males in hamadryas also disperse, but much less commonly than in R. roxellana. Provisioning may have influenced results, and confirming studies on unprovisioned groups would be valuable.

Chest Color and Social Status in Male Geladas (Theropithecus gelada)

Conspicuous colored patches on animals often serve as sexually selected signals that advertise male quality. Such colored traits facilitate assessment of risks associated with a specific contest or benefits associated with a specific mate choice. Here, we investigate whether a colored patch of skin on the chests of male geladas (Theropithecus gelada) is a sexually selected signal. Specifically, we examine the relationship between color (redness), social status (a proxy for reproductive success), and age. We use observational data from known individuals from a population of wild geladas living in Ethiopia. We digitally quantified chest color using a previously-validated method for measuring color under field conditions. Results from this study are consistent with the hypothesis that redness is a quality signal in males. Baseline color correlates with status even when controlling for age. Indeed, males with redder chests were members of “better” groups: 1) leader males—the only males with reproductive access to females—had the reddest chests, and 2) within leader males, males with large units (>6 females) had redder chests than males with small units. At present, we are unable to address whether male chest color is directed at potential rivals or mates. Nevertheless, our data support the hypothesis that quality signals should prevail in large, fluid groups, where it is unlikely that individuals recognize all other group members. If individual recognition is limited in gelada society, this would favor the evolution of alternative means of assessment for making reproductive decisions.

The fourth level of social structure in a multi‐level society: ecological and social functions of clans in hamadryas baboons

Hamadryas baboons are known for their complex, multi-level social structure consisting of troops, bands, and one-male units (OMUs) [Kummer, 1968. Social organization of hamadryas baboons. Chicago: The University of Chicago Press. 189p]. Abegglen [1984. On socialization in hamadryas baboons: a field study. Lewisburg, PA: Bucknell University Press. 207p.] observed a fourth level of social structure comprising several OMUs that rested near one another on sleeping cliffs, traveled most closely together during daily foraging, and sometimes traveled as subgroups independently from the rest of the band. Abegglen called these associations "clans" and suggested that they consisted of related males. Here we confirm the existence of clans in a second wild hamadryas population, a band of about 200 baboons at the Filoha site in lowland Ethiopia. During all-day follows from December 1997 through September 1998 and March 2005 through February 2006, data were collected on activity patterns, social interactions, nearest neighbors, band fissions, and takeovers. Association indices were computed for each dyad of leader males, and results of cluster analyses indicated that in each of the two observation periods this band comprised two large clans ranging in size from 7 to 13 OMUs. All band fissions occurred along clan lines, and most takeovers involved the transfer of females within the same clan. Our results support the notion that clans provide an additional level of flexibility to deal with the sparse distribution of resources in hamadryas habitats. The large clan sizes at Filoha may simply be the largest size that the band can split into and still obtain enough food during periods of food scarcity. Our results also suggest that both male and female relationships play a role in the social cohesion of clans and that males exchange females within clans but not between them.

Dominance relationships among male hamadryas baboons (Papio hamadryas)

The concept of dominance has been shown to be useful in describing and predicting social interactions in group-living animals. However, the dominance relationships among adult hamadryas males (Papio hamadryas) are poorly understood, and systematic data are missing from the literature. This study investigated dominance relationships among male hamadryas baboons by applying novel statistical techniques to systematic detailed data on agonistic interactions. We also analyzed the dominance relationship with male age and evaluated the association between dominance and access to mating partners (i.e. the number of adult females per one-male unit (OMU)), food resources (i.e. monopolization of feeding areas), and greeting interactions. The derived dominance indexes showed that, in general, leader males were dominant over followers, and that dominance ability did not correlate with male age. Individual dominance values were very close to each other, suggesting that dominance relationships among hamadryas males were not very rigid. In addition, dominance values were positively correlated with number of adult females per OMU but not with feeding priority. Finally, greeting interactions occurred more frequently between individuals with similar dominance values and with low levels of dominance decidedness. We suggest the need of further studies, especially in wild populations, to confirm our findings.

Postconflict Affiliation of Aggressors in Papio hamadryas

Researchers have associated variation in the occurrence of postconflict behaviors with variation in the relationship quality between involved individuals. Apart from those on the great apes, the vast majority of postconflict studies involved female-bonded species and focused on the victim. We examined postconflict affiliation involving the aggressor in a non-female-bonded species, hamadryas baboons (Papio hamadryas), and investigated the influence of relationship quality on the occurrence of 2 types of postconflict affiliative behaviors. Hamadryas baboons reconciled after a conflict and the highest rate of reconciliation was between one-male unit (OMU) leader males and their females. Via direct measures of relationship characteristics we also found that partners with higher-quality relationship, e.g., highly affiliative dyads and allies, showed higher levels of conciliatory tendency than dyads with lower-quality relationship, e.g., less affiliative dyads and non-allies. We found evidence of postconflict third-party affiliation initiated by aggressors, but not by third parties. Further, aggressor-initiated affiliation was more likely with individuals of the same OMU and individuals with which the aggressor maintained a strongly affiliative relationship. Our findings provide further support for relationship quality as a fundamental underlying factor not only in reconciliation, but also in postconflict affiliations involving third parties.

Chirp rate is independent of male condition in a synchronising bushcricket

Males of the bushcricket Mecopoda elongata synchronise their chirps with neighbouring males, but because synchrony is imperfect, one male's chirp preceeds the other by some 50–200 ms. Since a male's intrinsic chirp rate is critical for the establishment of the leader role in a duet, and females prefer the leader in a choice situation, we investigated a possible condition dependence of this male trait. In a duet leader males are usually those calling at a higher intrinsic rate; therefore, we investigated whether calling at a higher rate indicates male condition. The calling metabolism was quantified in a respirometer; the factorial slope of males calling at a high rate was three times higher compared to males calling at lower rates. Males produce on average 3.4 singing bouts/per night, and there is a significant increase in chirp periods (CPs) with successive singing bouts. Call properties were investigated throughout a male's life; chirp period increases significantly with age. Two groups of males were reared on either a low- or a high-nutrition diet, and the influence of male condition on different song parameters was investigated. CPs in two feeding regimes did not differ significantly, although males of the low-nutrition diet group were significantly affected by nutrition with respect to mortality, a delayed last moult and reduced weight as adults. We therefore conclude that solo chirp rates do not reflect phenotypic male condition properly.