Grooming and Anxiety in Barbary Macaques

Grooming is a fundamental component of sociality in many gregarious animal species, and elucidating the costs and benefits of this behaviour is crucial for understanding its function. There is evidence that animals giving grooming pay a cost in terms of the time and energy they invest, while recipients benefit not just from the removal of dirt and parasites, but also from the relaxing effects of being groomed. Recently, however, studies of primates have indicated that giving grooming may also provide such hedonic benefits, reducing levels of stress or anxiety in the groomer. In this study of free‐ranging adult female Barbary macaques at Trentham Monkey Forest (Stoke‐on‐Trent, UK), we tested the hypothesis that grooming reduces anxiety in the donor and/or the recipient. During focal follows, we quantified females' rates of self‐scratching as a behavioural index of their anxiety levels. Self‐scratching rates in the 2‐min periods after bouts of grooming (given, received and reciprocated) were compared to overall mean self‐scratching rates; we predicted that if grooming reduces anxiety, self‐scratching rates would be significantly lower after grooming bouts than mean levels. We first analysed all grooming bouts and then analysed separately grooming bouts with adult males, with all adult females, with subordinate adult females and with dominant adult females. Contrary to our prediction, self‐scratching rates were never seen to be lower after grooming than mean levels. In fact, for the majority of grooming partner–direction combinations, we found significantly higher rates of self‐scratching after grooming compared to mean levels. The hypothesis that grooming reduces anxiety was therefore not supported. Grooming seems in some cases to increase, not alleviate, anxiety. We explore possible explanations for these unexpected results.     

Complex patterns of grooming and sexual activity in Barbary macaques (Macaca sylvanus)

Grooming in primates is often considered a “currency” that can be exchanged for other “services” or “commodities” such as reciprocal grooming, coalitionary support, infant handling, tolerance around food sources, active food sharing, or mating opportunities. Previous studies on primate grooming‐for‐sex exchange viewed the males as the demanding class, with the females as suppliers of mating opportunities. In this study, we examine the broader context of grooming‐for‐mating exchange in Barbary macaques in Gibraltar. Our data show that Barbary macaque males groom females with whom they are mating more frequently and for longer periods than other females, and the relationship between grooming and mating remains significant in both sexual and nonsexual contexts. In addition, females groomed males with whom they were mating more frequently and for longer periods than other males. In both sexes, grooming was observed to be far more frequent and to occur for longer durations in sexual compared to nonsexual contexts. We did not find any difference in grooming behavior between presexual and postsexual contexts. Our data suggest that there is no simple model to describe Barbary macaque grooming patterns in sexual contexts. Although our results are partly consistent with male use of grooming as payment for mating, broadly assessed grooming‐mating patterns cannot be solely explained by a male‐driven grooming‐for‐mating exchange.     

Dominance hierarchy and social relationships in a group of Captive black-and-white snub-nosed monkeys (Rhinopithecus bieti)

Different types of dominance hierarchies reflect different social relationships in primates. In this study, we clarified the hierarchy and social relationships in a one-male unit of captive Rhinopithecus bieti observed between August 1998 and March 1999. Mean frequency of agonistic behaviour among adult females was 0.13 interactions per hour. Adult females exhibited a linear hierarchy with a reversal of 10.9%, indicating an unstable relationship; therefore, R. bieti appears to be a relaxed/tolerant species. The lack of a relationship between the agonistic ratio of the adult male towards adult females and their ranks indicated that males did not show increased aggression towards low-ranking females. Differentiated female affiliative relationships were loosely formed in terms of the male, and to some extent influenced by female estrus, implying that relationships between the male and females is influenced by estrus and not rank alone. A positive correlation between the agonistic ratio of adult females and their ranks showed that the degree to which one female negatively impacted others decreased with reduction in rank. Similarly, a positive correlation between the agonistic ratio of females and differences in rank suggests that a female had fewer negative effects on closely ranked individuals than distantly ranked ones. These data indicate that rank may influence relationships between females. A steeper slope of regression between the agonistic ratio and inter-female rank differences indicated that the extent of the power difference in high-ranking females exerting negative effects on low-ranking ones was larger during the mating season than the birth season, suggesting that rank may influence the mating success of females.     

Queuing and queue-jumping: long-term patterns of reproductive skew in male savannah baboons, Papio cynocephalus

In many animals, variance in male mating success is strongly correlated with male dominance rank or some other measure of fighting ability. Studies in primates, however, have varied greatly in whether they detect a relationship between male dominance rank and mating success. This variability has led to debate about the nature of the relation between rank and mating success in male primates. We contribute to the resolution of this debate by presenting an analysis of the relationship between dominance rank and male mating success over 32 group-years in a population of wild savannah baboons. When data were pooled over the entire period, higher-ranking males had greater access to fertile females. However, when we examined successive 6-month blocks, we found variance in the extent to which rank predicted mating success. In some periods, the dominance hierarchy functioned as a queue in which males waited for mating opportunities, so that rank predicted mating success. In other periods, the queuing system broke down, and rank failed to predict mating success when many adult males were in the group, when males in the group differed greatly in age, and when the highest-ranking male maintained his rank for only short periods. The variance within this single population is similar to the variance observed between populations of baboons and between species of primates. Our long-term results provide strong support for the proposition that this variance is not an artefact of methodological differences between short-term studies, but is due to true variance in the extent to which high-ranking males are able to monopolize access to females. Copyright 2003 Published by Elsevier Science Ltd on behalf of The Association for the Study of Animal Behaviour.     

Testosterone and reproductive effort in male primates

Considerable evidence suggests that the steroid hormone testosterone mediates major life-history trade-offs in vertebrates, promoting mating effort at the expense of parenting effort or survival. Observations from a range of wild primates support the “Challenge Hypothesis,” which posits that variation in male testosterone is more closely associated with aggressive mating competition than with reproductive physiology. In both seasonally and non-seasonally breeding species, males increase testosterone production primarily when competing for fecund females. In species where males compete to maintain long-term access to females, testosterone increases when males are threatened with losing access to females, rather than during mating periods. And when male status is linked to mating success, and dependent on aggression, high-ranking males normally maintain higher testosterone levels than subordinates, particularly when dominance hierarchies are unstable. Trade-offs between parenting effort and mating effort appear to be weak in most primates, because direct investment in the form of infant transport and provisioning is rare. Instead, infant protection is the primary form of paternal investment in the order. Testosterone does not inhibit this form of investment, which relies on male aggression. Testosterone has a wide range of effects in primates that plausibly function to support male competitive behavior. These include psychological effects related to dominance striving, analgesic effects, and effects on the development and maintenance of the armaments and adornments that males employ in mating competition.     

Mating Tactics in Response to Costs Incurred by Mating with Multiple Males in Wild Female Japanese Macaques

We investigated the costs of mating with multiple males in terms of feeding time, traveling distances, sexual proceptivity, and male aggression, for wild female (Macaca fuscata yakui) on Yakushima Island, Japan. We analyzed all-day focal sampling data from 7 females during the mating season (Sept.-Nov. 1996). On days when estrous females copulated with multiple males, they decreased their feeding time to half that of anestrous days, traveled longer distances, showed more proceptive sexual behaviors and received more aggression from subordinate males than on days when they copulated with only the 1st-ranking male. On days when females copulated with only the 1st-ranking male, they showed no difference in feeding time with that of anestrous days, and expended less effort than the above mating pattern because of short traveling distances, diminished sexual proceptivity and a lower frequency of aggression received. The results suggest that the costs of estrous vary according to female sexual proceptivity and the number and social status of mating partners. Female Japanese macaques exhibit a mixed mating strategy over prolonged estrous periods, which may provide females with opportunities to maximize the benefits of copulating with multiple males and to minimize the costs of estrus by mating with only the 1st-ranking male. During an estrous cycle, females may be adjusting efforts for reproduction and survival; i.e., mating vs. feeding.     

Reproductive patterns in mantled howler monkeys: Estrus,mate choice and copulation

The present study was undertaken to evaluate non-random mating patterns in two groups of mantled howler monkeys in two tropical dry forest habitats. Sexual dimorphism, female estrus stage, male dominance rank, sexual solicitations and copulations were assessed. Males are significantly larger than females, but female weight varies more than male weight. The length of female estrus cycles is comparable in both habitats, but females in the more strongly seasonal habitat demonstrate greater estrus synchrony relative to their numbers. Males solicit potential mates more frequently than females, a pattern explained by the relatively high rate of sexual solicitation by high-ranking males. Females in “peak” estrus solicit “alpha” males, while females in other stages of estrus solicit males equally by rank. Intersexual aggression occurs rarely, and “forced copulations” are attempted but, apparently, are unsuccessful. Sexual solicitations by “alpha” males and “peak” estrus females are most likely to lead to copulation, and “alpha” males are more likely to copulate than “gamma” males. In general, latencies from first solicitation to copulation are expensive in time, especially for high-ranking males. Estimated annual reproduction success favors high-ranking males, and results indicate that male and female mating behavior is mutually coordinated and controlled.     

Perineal swellings: a social and endocrine advantage for Barbary macaque females (Macaca sylvanus)

This study focuses the relationship between social rank, intersexual behavior, age, fecal cortisol equivalent excretion rates and perineal swelling size in contraceptive-treated Macaca sylvanus females. Behavioral data and fecal samples were collected during a twenty-week period from 24 females. Females were categorized with regard to perineal swelling (enlarged or reduced), and to their dominance rank (high or low); we found that swelling size was not associated with it. However, females with an enlarged perineum received more male grooming interactions, had closer spatial relations to males, and received significantly more interventions from males than did the others. Endocrinologically, females with enlarged swelling showed decreased fecal cortisol equivalent excretion rates. Multiple regression models showed a positive relationship between the extent of the swelling size and grooming, inspection and spatial relation. There was a negative relationship between the extent of swelling size and fecal cortisol equivalents. These results imply that enlarged perineal swellings among implanted Barbary macaque females have a greater impact on intersexual contact and adrenocortical activity than does social rank or age.     

The Foraging Costs of Mating Effort in Male Chimpanzees (Pan troglodytes schweinfurthii)

Costs of mating effort can affect the reproductive strategies and lifetime fitness of male primates, but interspecific and interindividual variation in the magnitude and distribution of costs is poorly understood. Male costs have primarily been recognized in seasonally breeding species that experience concentrated periods of mating competition. Here, we examine foraging costs associated with male mating effort in chimpanzees (Pan troglodytes schweinfurthii), a polygynandrous species, in which mating opportunities occur intermittently throughout the year. To quantify male feeding, aggression, and mating, we conducted focal follows on 12 males in a wild community (Kanyawara, Kibale National Park, Uganda) for 11 mo. Males fed less on days when high-value mating opportunities (estrous parous females) were available than on days without any mating opportunities. Reductions in feeding time were related to increased rates of aggression and copulation, indicating that the proximate cause of changes in male foraging was mating effort. Surprisingly, however, there was no relationship between dominance rank and the extent to which feeding time was reduced. High costs of mating effort may reduce the degree of reproductive skew and limit the use of possessive tactics in chimpanzees. We suggest that male bonding in chimpanzees may be favored not only for its benefits but because intragroup competition is so costly. Our results complement the available data on mammals, and primates in particular, by showing that mating effort can have measurable foraging costs even in species, in which breeding is aseasonal and only moderately skewed.     

Correlates of Self-Directed Behaviour in Wild White-Faced Capuchins

Elevated rates of self‐directed behaviour (SDB) such as self‐scratching and autogrooming have been widely used in recent years as an indicator of anxiety in catarrhine primates. This study presents the first examination of correlates of SDB rates in a platyrrhine primate. Subjects were 8 wild female white‐faced capuchins at Lomas Barbudal, Costa Rica, who were observed for 119 h of focal individual follows. The subjects performed significantly more self‐scratching and autogrooming while in close proximity to conspecifics than while alone, irrespective of whether the neighbour was dominant or subordinate to them. This result was attributable to elevated SDB rates during the 30 s preceding and following allogrooming bouts. Furthermore, subjects engaged in more SDB while in proximity to females (a) that were closer to them in dominance rank and (b) with whom they spent a larger proportion of their time in proximity. Self‐directed behaviour rates after conflicts did not differ from non‐postconflict rates. Nor were SDB rates above baseline levels during the 30 s before subjects descended to the ground. These results may provide support for the view that SDB rates index anxiety in this species, if grooming decisions signal individuals' current allegiances and are therefore a source of anxiety, even if being groomed is, itself, relaxing. Postconflict preparation for further aggression may mitigate against scratching and autogrooming in a fast‐moving arboreal species.     

Mating season aggression and fecal testosterone levels in male ring-tailed lemurs (Lemur catta)

The challenge hypothesis (J. C. Wingfield, R. E. Hegner, B. G. Ball, and A. M. Duffy, 1990, Am. Nat. 136, 829-846) proposes that in birds, reptiles, and fish, "the frequency or intensity of reproductive aggression as an effect of T[estosterone] is strongest in situations of social instability, such as during the formation of dominance relationships, the establishment of territorial boundaries, or challenges by a conspecific male for a territory or access to mates" (p. 833). To determine the extension of this hypothesis to mammalian species, we tested predictions of the hypothesis in a nonpaternal, seasonal breeding, prosimian primate (ring-tailed lemurs, Lemur catta). Semi-free-ranging males were studied during periods of social stability (premating period) and instability (mating period). The annual mating season consists of several days during which males fight for access to promiscuous group females as each individually becomes sexually receptive for 1 day. Male rates of aggression were compared to fecal testosterone levels within premating and mating periods. In the premating period male rate of aggression was not significantly correlated with testosterone level. By contrast, during the mating season testosterone and aggression levels were positively and significantly correlated. However, on days just preceding estrus, male rate of aggression was not significantly correlated with testosterone, but on days of estrus, when aggressive challenges peaked sharply, testosterone and aggression were highly positively correlated. These results suggest that the challenge hypothesis applies to mammals as well as to birds, reptiles, and fish. In addition, elevations in testosterone were tightly circumscribed around days of estrus, suggesting a compromise between costs and benefits of elevated testosterone levels.     

Male Social Behavior and Dominance Hierarchy in the Sulawesi Crested Black Macaque (Macaca nigra)

In a 6-week study of the social behavior of wild Sulawesi crested black macaques (Macaca nigra), we found a linear and transitive dominance hierarchy among the six adult males in one social group. Dominance rank, as determined by the direction of supplantations, correlated strongly with percentage of time near more than four neighbors, frequency of grooming received from adult females, and percentage of time with an adult female as nearest neighbor. These results suggest that high-ranking males are socially attractive. Adult females sexually solicited high-ranking males more often than low-ranking males, but frequency of copulation was not correlated with dominance rank. Frequency and intensity of aggression between males are strongly correlated with rank distance, but aggression toward females was greatest for mid-ranking males. Males of all rank displayed significantly more aggression toward sexually receptive females than toward females in other estrous states. These data indicate that male Sulawesi crested black macaques display a social organization similar to that reported for multimale groups in other macaque species rather than the egalitarian social organization described for female Sulawesi macaques.     

Sexual behavior of the female porcupine Hystrix africaeaustralis

Porcupines are sexually active throughout the estrous cycle, and sexual behavior is not affected by the reproductive status and hormonal milieu of females. Increased female-male interactions during estrus are the only indications of behavioral changes during estrus. The lack of aggression shown by females to known males as opposed to aggression shown to strange males, the greater interest shown by males toward certain females, and the superior breeding success of these females suggest a pair-bonding mating system. Limited changes in female receptivity throughout the cycle might be of importance in maintaining the pair-bond.     

Effects of the distribution of female primates on the number of males

The spatiotemporal distribution of females is thought to drive variation in mating systems, and hence plays a central role in understanding animal behavior, ecology and evolution. Previous research has focused on investigating the links between female spatiotemporal distribution and the number of males in haplorhine primates. However, important questions remain concerning the importance of spatial cohesion, the generality of the pattern across haplorhine and strepsirrhine primates, and the consistency of previous findings given phylogenetic uncertainty. To address these issues, we examined how the spatiotemporal distribution of females influences the number of males in primate groups using an expanded comparative dataset and recent advances in bayesian phylogenetic and statistical methods. Specifically, we investigated the effect of female distributional factors (female number, spatial cohesion, estrous synchrony, breeding season duration and breeding seasonality) on the number of males in primate groups. Using bayesian approaches to control for uncertainty in phylogeny and the model of trait evolution, we found that the number of females exerted a strong influence on the number of males in primate groups. In a multiple regression model that controlled for female number, we found support for temporal effects, particularly involving female estrous synchrony: the number of males increases when females are more synchronously receptive. Similarly, the number of males increases in species with shorter birth seasons, suggesting that greater breeding seasonality makes defense of females more difficult for male primates. When comparing primate suborders, we found only weak evidence for differences in traits between haplorhines and strepsirrhines, and including suborder in the statistical models did not affect our conclusions or give compelling evidence for different effects in haplorhines and strepsirrhines. Collectively, these results demonstrate that male monopolization is driven primarily by the number of females in groups, and secondarily by synchrony of female reproduction within groups.     

Alpha male chimpanzee grooming patterns: implications for dominance “style”

In social primates, individuals use various tactics to compete for dominance rank. Grooming, displays and contact aggression are common components of a male chimpanzee's dominance repertoire. The optimal combination of these behaviors is likely to differ among males with individuals exhibiting a dominance “style” that reflects their tendency to use cooperative and/or agonistic dominance tactics. Here, we examine the grooming behavior of three alpha male chimpanzees at Gombe National Park, Tanzania. We found that (1) these males differed significantly in their tendency to groom with other males; (2) each male's grooming patterns remained consistent before, during and after his tenure as alpha, and (3) the three males tended to groom with high‐ middle‐ and low‐ranking partners equally. We suggest that body mass may be one possible determinant of differences in grooming behavior. The largest male exhibited the lowest overall grooming rates, whereas the smallest male spent the most time grooming others. This is probably because large males are more effective at physically intimidating subordinates. To achieve alpha status, a small male may need to compensate for reduced size by investing more time and energy in grooming, thereby ensuring coalitionary support from others. Rates of contact aggression and charging displays conformed to this prediction, suggesting that each male exhibited a different dominance “style.” Am. J. Primatol. 71:136–144, 2009. © 2008 Wiley‐Liss, Inc.     

Concealed fertility and extended female sexuality in a non-human primate (Macaca assamensis)

In numerous primates living in mixed-sex groups, females display probabilistic cues of fertility to simultaneously concentrate paternity to dominant males while diluting it amongst others as a means to reduce the risk of infanticide and to increase male care for offspring. A few species, however, lack these cues and potentially conceal fertility from males; yet, to date, little is known about mating patterns and their underlying proximate mechanisms in such species. Here, we investigated mating activity and sexual consortships relative to female reproductive state in wild Assamese macaques (Macaca assamensis), a species where females lack prominent anogenital swellings and copulation calls. During two mating seasons (2837 contact hours) we recorded sexual and social behaviors, sexual consortships, and collected 1178 fecal samples (n = 15 females) which were analyzed for progestogen concentrations to assess female reproductive state and to determine the timing of ovulation and conception. Although mostly conceiving in their first ovarian cycle, females were sexually receptive throughout the entire 4-month mating season, and within-cycle mating frequencies were not increased during fertile phases. Dominant males did not monopolize fertile matings, and consortships by high-ranking males lasted for long periods, which were not exclusively linked to female fertile phases. Furthermore, females copulated promiscuously but not randomly, i.e. for almost every female, matings were concentrated to a certain male, irrespective of male rank. Collectively, we demonstrate that fertility is undisclosed to males. The extreme extended female sexuality facilitated by concealed fertility may allow females to create differentiated mating relationships within a promiscuous mating system. Our study provides important new insight into the plasticity of female sexuality in non-human primates.     

Special relationships instead of female dominance for redfronted lemurs,Eulemur fulvus rufus

Most lemurs yet studied in detail exhibit some mode of adult female social dominance over males. The known exception, a brown lemur subspecies known as rufous or redfronted lemurs (Eulemur fulvus rufus), forms multimale–multifemale social groups within which unambiguous dominance relations are not observed among adults. Resting groups of redfronted lemurs consistently include huddling adult male–female pairs whose males selectively scentmark and rub their heads in the scentmarks of their female huddling partners. Quantitative observations confirmed that some of these male–female pairs maintain special relationships satisfying all criteria originally developed in research on cercopithecine monkeys. Observations before, during, and after mating season, intergroup encounters, male transfers, and changes in male–female affiliations illuminated developmental and functional aspects of male–female partnerships. Each adult female in two semi-free-ranging study groups shared high rates of association, grooming, and agonistic support and low rates of agonistic interaction with one unrelated or distantly related adult male partner. Such affinity characterized small proportions of adult male–female relationships. Several males directed not only support but also aggression toward adult females with whom they sought to affiliate. All bonded males sought to copulate with their partners, and some appeared to ignore estrus in nonpartners. All females accepted copulation attempts from partners and some seemed to prefer their partners as mates. Partial synchronization of brief estrus periods together with concealed ovulation appeared to minimize chances for polygynous mating. Results support the view that the male–female pair is the fundamental social unit of E. fulvus and suggest that female partnership with individual males obviates dominance behavior, including female dominance, in this lemurid primate. Am. J. Primatol. 43:239–258, 1997. © 1997 Wiley-Liss, Inc.     

Female bonobos use copulation calls as social signals

During mating events, females of many primate species produce loud and distinct vocalizations known as 'copulation calls'. The adaptive significance of these signals is considered to be in promoting the caller's direct reproductive success. Here, we investigated copulation calling in bonobos (Pan paniscus), a species in which females produce these vocalizations during sexual interactions with partners of both sexes. Females were more likely to call when mating with males than with females. We also observed a positive relationship between the likelihood of calling and partner rank, regardless of partner sex. Sexual activity generally increased with swelling size (an indicator of reproductive state) and, during their peak swelling, females called more with male than with female partners. Female bonobos are unusual among the non-human primates in terms of their heightened socio-sexuality. Our results suggest that in this species, copulation calls have undergone an evolutionary transition from a purely reproductive to a more general social function, reflecting the intrinsic evolutionary links between vocal behaviour and social cognition.     

Female parity, male aggression, and the Challenge Hypothesis in wild chimpanzees

The Challenge Hypothesis proposes that testosterone mediates aggression during periods of heightened conflict between males, especially episodes that have important fitness consequences. Considerable evidence from seasonally breeding species provides support for this hypothesis, but few data exist in animals that mate year-round. We tested predictions generated by the Challenge Hypothesis in chimpanzees, a non-seasonally breeding primate, through a study of individuals living in an exceptionally large community at Ngogo, Kibale National Park, Uganda. Results indicated that dominance rank had no influence on testosterone levels. Instead of rank influencing testosterone production, additional analyses revealed an important role for reproductive competition. Male chimpanzees displayed more aggression when they were in the same party as parous estrous females than when reproductively active females were unavailable. Male chimpanzees competed more intensely for mating opportunities with parous females than with nulliparas, and as a consequence, males displayed more aggression around the former than the latter. When males accompanied parous estrous females, their urinary testosterone concentrations were significantly higher than baseline concentrations. In contrast, urinary testosterone concentrations did not exceed baseline when males associated with nulliparous estrous females. These differences in testosterone levels could not be attributed to mating per se because males copulated equally often with parous and nulliparous females. Furthermore, variation in testosterone concentrations were not due to males gathering together in large parties, as their levels in these situations did not exceed baseline. Taken together, these findings, derived from a relatively large sample of males and estrous females, replicate those from a prior study and furnish additional support for the Challenge Hypothesis. Our results suggest that the Challenge Hypothesis is likely to be broadly applicable to chimpanzees and increase our understanding of the physiological costs to males who compete for estrous females.     

Variation in fecal testosterone levels, inter-male aggression, dominance rank and age during mating and post-mating periods in wild adult male ring-tailed lemurs (Lemur catta)

In primate species exhibiting seasonal reproduction, patterns of testosterone excretion in adult males are variable: in some species, peaks correlate with female receptivity periods and heightened male-male aggression over access to estrous females, in others, neither heightened aggression nor marked elevations in testosterone have been noted. In this study, we examined mean fecal testosterone ( f T) levels and intermale aggression in wild adult male ring-tailed lemurs residing in three groups at Beza Mahafaly Reserve, Madagascar. Results obtained from mating and post-mating season 2003 were compared to test Wingfield et al. [1990. Am Nat 136:829-846] "challenge hypothesis", which predicts a strong positive relationship between male testosterone levels and male-male competition for access to receptive females during breeding season. f T levels and rates of intermale aggression were significantly higher during mating season compared to the post-mating period. Mean f T levels and aggression rates were also higher in the first half of the mating season compared with the second half. Number of males in a group affected rates of intermale agonism, but not mean f T levels. The highest-ranking males in two of the groups exhibited higher mean f T levels than did lower-ranking males, and young males exhibited lower f T levels compared to prime-aged and old males. In the post-mating period, mean male f T levels did not differ between groups, nor were there rank or age effects. Thus, although male testosterone levels rose in relation to mating and heightened male-male aggression, f T levels fell to baseline breeding levels shortly after the early mating period, and to baseline non-breeding levels immediately after mating season had ended, offsetting the high cost of maintaining both high testosterone and high levels of male-male aggression in the early breeding period.