Lifetime individual plasticity in body condition of a migratory bird

Body condition is an important trait that reflects the capacity of individuals to acquire food or resist disease, eventually allowing successful reproduction and survival. We first quantified the effects of condition on life history and a secondary sexual trait using long‐term lifetime data on condition in a migratory bird species, the barn swallow, Hirundo rustica. Second, we quantified sources of individual variation in condition by separating the within‐individual from the between‐individual components of variation of environmental condition and age on body condition. Therefore, we were able to partition variation as a result of selection and phenotypic plasticity. Within‐individual variation in body condition increased in early life until middle age (i.e. 3–4 years of age) in the two sexes followed by only a slight decrease in body condition during senescence in males but not in females. After accounting for age‐dependent variation, condition could be partitioned into a within‐individual plastic response to environmental conditions during migration and a nonplastic response (i.e. a between‐individual difference) to environmental conditions experienced in the African winter quarters. Specifically, there was a within‐individual increase in body condition as environmental conditions during migration improved in both males and females, independent of age. There was a between‐individual effect of condition found in the winter quarter in body condition of females, but not in males, which was attributed to the disappearance of females in poor body condition from the study population as a result of the higher natal dispersal of low‐quality females compared to high‐quality ones during years with favourable environmental conditions in the African winter quarters. Males and females also tended to be in better body condition during the warmer springs upon arrival at the breeding grounds. There was a temporal decline in female body condition during 1991–2007, whereas no significant trend was detected in males. Therefore, both intrinsic (e.g. age and sex) and extrinsic factors (e.g. climate) affected body condition. © 2011 The Linnean Society of London, Biological Journal of the Linnean Society, 2012, 105 , 420–434.     

Cold tolerance,and not earlier arrival on breeding grounds,explains why males winter further north in an Arctic‐breeding songbird

Sex biases in distributions of migratory birds during the non‐breeding season are widespread; however, the proximate mechanisms contributing to broad‐scale sex‐ratio variation are not well understood. We analyzed a long‐term winter‐banding dataset in combination with spring migration data from individuals tracked by using geolocators to test three hypotheses for observed variation in sex‐ratios in wintering flocks of snow buntings Plectrophenax nivalis. We quantified relevant weather conditions in winter (temperature, snowfall and snow depth) at each banding site each year and measured body size and condition (fat scores) of individual birds (n > 5500). We also directly measured spring migration distance for 17 individuals by using light‐level geolocators. If the distribution pattern of birds in winter is related to interactions between individual body size and thermoregulation, then larger bodied birds (males) should be found in colder sites (body size hypothesis). Males may also winter closer to breeding grounds to reduce migration distance for early arrival at breeding sites (arrival timing hypothesis). Finally, males may be socially dominant over females, and thus exclude females from high‐quality wintering sites (social dominance hypothesis). We found support for the body size hypothesis, in that colder and snowier weather predicted both larger body size and higher proportions of males banded. Direct tracking revealed that males did not winter significantly closer to their breeding site, despite being slightly further north on average than females from the same breeding population. We found some evidence for social dominance, in that females tended to carry more fat than males, potentially indicating lower habitat quality for females. Global climatic warming may reduce temperature constraints on females and smaller‐bodied males, resulting in broad‐scale changes in distributional patterns. Whether this has repercussions for individual fitness, and therefore population demography, is an important area of future research.     

Winter body condition in relation to age,sex and plumage ornamentation in a migratory songbird

Winter body condition may play important roles in the life history of migratory birds, but it is difficult to estimate. We used the growth rate of winter‐grown tail feathers of Collared Flycatchers Ficedula albicollis as an indicator of winter body condition, comparing this trait between age classes and sexes and relating it to plumage ornamentation (forehead and wing patch sizes). Adults and males were in better nutritional condition during winter, as indicated by their faster tail feather growth rates, than were yearlings and females, respectively, which could indicate differences in individual quality and foraging ability with age, or age‐ and sex‐related winter habitat segregation. However, feather growth rate was related neither to the size of the winter‐grown forehead patch nor to the size of the summer‐grown wing patch, suggesting weak condition‐dependence for the winter‐grown ornament and complex life‐history consequences for the summer‐grown ornament.     

Carry‐over effects of winter habitat quality on en route timing and condition of a migratory passerine during spring migration

We examined how conditions prior to migration influenced migration performance of two breeding populations of black‐and‐white warblers Mniotilta varia by linking information on the migrant's winter habitat quality, measured via stable carbon isotopes, with information on their breeding destination, measured via stable hydrogen isotopes. The quality of winter habitat strongly influenced the timing of migration when we accounted for differential timing of migration between breeding populations. Among birds migrating to the same breeding destination, males and females arriving early to the stopover site originated from more mesic habitat than later arriving birds, suggesting that the benefits of occupying high‐quality mesic habitat during the winter positively influence the timing of migration. However, male warblers arriving early to the stopover site were not in better migratory condition than later arriving conspecifics that originated from poor‐quality xeric winter habitat, regardless of breeding destination. The two breeding populations stopover at the study site during different time periods, suggesting that the lower migratory condition of early birds is not a function of the time of season, but potentially a migrant's migration strategy. Strong selection pressures to arrive early on the breeding grounds to secure high‐quality breeding territories may drive males from high‐quality winter habitat to minimize time at the expense of energy. This migration strategy would result in a smaller margin of safety to buffer the effects of adverse weather or scarcity of food, increasing the risk of mortality. The migratory condition of females was the same regardless of the timing of migration or breeding destination, suggesting that females adopt a strategy that conserves energy during migration. This study fills an important gap in our understanding of the linkages between winter habitat quality and factors that influence the performance of migration, the phase of the annual cycle thought to be limiting most migratory bird populations.     

Female butterflies modulate investment in reproduction and flight in response to monsoon‐driven migrations

Migratory species may display striking phenotypic plasticity during individual lifetimes. This may include differential investment in body parts and functions, differential resource use and allocation, and behavioural changes between migratory and non‐migratory phases. While migration‐related phenotypic changes are well‐reported, their underlying mechanisms are usually poorly understood. Here we compare individuals from migratory (reproductive diapause) and non‐migratory (reproductive) phases of closely related aposematic butterfly species to study how sexual dimorphism and migratory behaviour underlie significant morphological tradeoffs, and propose a plausible scenario to explain the migration‐related phenotypic plasticity observed in females of migratory species. We found that female butterflies invested significantly more in their abdominal mass compared to males irrespective of their migratory phase, and underwent a clear shift in their body mass allocation after the switch from the reproductive diapause phase to the reproductive phase. In reproductive phase, females invested much more in reproductive tissue. This switch occurred as a result of increased abdominal mass (i.e. reproductive tissue mass) without significant reduction in the thoracic mass (i.e. flight muscle mass). Migratory males, however, were not significantly different from non‐migratory males in terms of relative investment in flight and reproductive tissues. These patterns were consistent between migratory and non‐migratory aposematic species within and across clades. While migratory habits may influence the physiology and behaviour of both sexes, long‐distance migration affected female morphology much more markedly compared to that of males. These results show the sex‐specific nature of adaptations to migratory behaviour, and suggest that seemingly disparate life‐history traits such as aposematism and migration may have similar influences on the lifetime energetic investments of insects.     

Tracking Post-Hibernation Behavior and Early Migration Does Not Reveal the Expected Sex-Differences in a “Female-Migrating” Bat

Long-distance migration is a rare phenomenon in European bats. Genetic analyses and banding studies show that females can cover distances of up to 1,600 km, whereas males are sedentary or migrate only short distances. The onset of this sex-biased migration is supposed to occur shortly after rousing from hibernation and when the females are already pregnant. We therefore predicted that the sexes are exposed to different energetic pressures in early spring, and this should be reflected in their behavior and physiology. We investigated this in one of the three Central European long-distance migrants, the common noctule (Nyctalus noctula) in Southern Germany recording the first individual partial migration tracks of this species. In contrast to our predictions, we found no difference between male and female home range size, activity, habitat use or diet. Males and females emerged from hibernation in similar body condition and mass increase rate was the same in males and females. We followed the first migration steps, up to 475 km, of radio-tagged individuals from an airplane. All females, as well as some of the males, migrated away from the wintering area in the same northeasterly direction. Sex differences in long-distance migratory behavior were confirmed through stable isotope analysis of hair, which showed greater variation in females than in males. We hypothesize that both sexes faced similarly good conditions after hibernation and fattened at maximum rates, thus showing no differences in their local behavior. Interesting results that warrant further investigation are the better initial condition of the females and the highly consistent direction of the first migratory step in this population as summering habitats of the common noctule occur at a broad range in Northern Europe. Only research focused on individual strategies will allow us to fully understand the migratory behavior of European bats.     

Liking the good guys: amplifying local adaptation via the evolution of condition‐dependent mate choice

Local adaptation can be strengthened through a diversity of mechanisms that reduce gene flow between contrasting environments. Recent work revealed that mate choice could enhance local adaptation when females preferentially mate with locally adapted males and that such female preferences readily evolve, but the opposing effects of recombination, migration and costs of female preferences remain relatively unexplored. To investigate these effects, we develop a two‐patch model with two genes, one influencing an ecological trait and one influencing female preferences, where both male signals and female preferences are allowed to depend on the match between an individual's ecological trait and the local environment (condition). Because trait variation is limited when migration is rare and the benefits of preferential mating are short‐lived when migration is frequent, we find that female preferences for males in high condition spread most rapidly with intermediate levels of migration. Surprisingly, we find that preferences for locally adapted males spread fastest with higher recombination rates, which contrasts with earlier studies. This is because a stronger preference allele for locally adapted males can only get uncoupled from maladapted ecological alleles following migration through recombination. The effects of migration and recombination depend strongly on the condition of the males being chosen by females, but only weakly on the condition of the females doing the choosing, except when it comes to the costs of preference. Although costs always impede the spread of female preferences for locally adapted males, the impact is substantially lessened if costs are borne primarily by females in poor condition. The abundance of empirical examples of condition‐dependent mate choice combined with our theoretical results suggests that the evolution of mate choice could commonly facilitate local adaptation in nature.     

Highly dynamic wintering strategies in migratory geese: Coping with environmental change

When and where to move is a fundamental decision to migratory birds, and the fitness‐related costs and benefits of migratory choices make them subject to strong selective forces. Site use and migration routes are outcomes of opportunities in the surrounding landscape, and the optimal migration strategy may be conservative or explorative depending on the variability in the environment occupied by the species. This study applies 25 years of resighting data to examine development in winter migration strategy of pink‐footed geese divided among Denmark, the Netherlands and Belgium, and analyse potential drivers of strategy change as well as individuals’ likelihood to break with migratory tradition. Contrary with the general notion that geese are highly traditional in their winter site use, our results reveal that winter migration strategy is highly dynamic in this species, with an average annual probability of changing strategy of 54%. Strategy was not related to hunting pressure or winter temperature, but could be partly explained by a tracking of food resources in a landscape of rapid land use changes. The probability of individuals changing strategy from year to year varied considerably between birds, and was partly related to sex and age, with young males being the most likely to change. The annual probability of changing wintering strategy increased substantially from ≈40% to ≈60% during the study period, indicating an increasingly explorative behaviour. Our findings demonstrate that individual winter strategies are very flexible and able to change over time, suggesting that phenotypic plasticity and cultural transmission are important drivers of strategy choice in this species. Growing benefits from exploratory behaviours, including the ability to track rapid land use changes, may ultimately result in increased resilience to global change.     

Non‐Conceptive Sexual Behavior in Spiders: A Form of Play Associated with Body Condition,Personality Type,and Male Intrasexual Selection

In the socially polymorphic spider Anelosimus studiosus, males mature early in the reproductive season and recruit to the webs of juvenile females and guard them until they mature. During the period before females mature, males and females engage in repeated bouts of non‐conceptive (play) sexual behavior, where the pair courts and engages in mock copulation; both males and females gain performance‐enhancing experience via these encounters. In this study, we examined the factors that underlie individual variation in the tendency to engage in non‐conceptive mating and determine whether it impacts male–male competition for females. We found that docile females, being less resistant to mating in general, are more likely to accept male courtship and non‐conceptive copulation as juveniles. Personality type influenced the exhibition of non‐conceptive sexual behavior in males as well. High body condition males of the aggressive phenotype were more likely to engage in non‐conceptive sexual behavior than males with lower body condition. Body condition did not influence docile males’ propensity to engage in non‐conceptive sexual behavior, but female size did. Docile males engaged in more non‐conceptive sexual displays with larger females. Engaging in non‐conceptive sexual displays negatively impacted male performance in staged male–male contests for access to females. This cost was greatest for males of the aggressive phenotype, which are otherwise favored in male–male contests. Our findings indicate expression of non‐conceptive sexual displays is linked to personality and results in reproductive performance trade‐offs for male A. studiosus.     

The cost of migratory prey: seasonal changes in semi‐domestic reindeer distribution influences breeding success of Eurasian lynx in northern Norway

Migratory prey is a widespread phenomenon that has implications for predator–prey interactions. By creating large temporal variation in resource availability between seasons it becomes challenging for carnivores to secure a regular year‐round supply of food. Some predators may respond by following their migratory prey, however, most predators are sedentary and experience strong seasonal variation in resource availability. Increased predation on alternative prey may dampen such seasonal resource fluctuations, but reduced reproduction rates in predators is a predicted consequence of migratory primary prey behavior that has received little empirical attention. We used data from 23 GPS collared Eurasian lynx Lynx lynx monitored during 2007–2013 in northern Norway, to examine how spatio‐temporal variation in the migratory behavior of semi‐domestic reindeer Rangifer tarandus influences lynx spatial organization and reproductive success using estimates of seasonal home range overlap and breeding success. We found that lynx of both sexes maintained seasonally stable home ranges and exhibited site fidelity across years, independent of whether they had access to reindeer throughout the year or experienced a scarcity of reindeer in winter due to migration. However, lynx without access to reindeer in winter showed a decreased probability of reproducing and a tendency for lowered kitten survival into their first winter, when compared to female lynx with reindeer available year around. This supports the hypothesis that sedentary predators experience demographic costs in systems with migratory primary prey. Changes in the migratory behavior of ungulates, including disrupted migrations, is therefore likely to have bottom–up effects on the population dynamics of sedentary predators as well as the previously documented consequences for ungulate population dynamics.     

Migratory decisions in birds: extent of genetic versus environmental control

Migration is one of the most spectacular of animal behaviors and is prevalent across a broad array of taxa. In birds, we know much about the physiological basis of how birds migrate, but less about the relative contribution of genetic versus environmental factors in controlling migratory tendency. To evaluate the extent to which migratory decisions are genetically determined, we examined whether individual western burrowing owls (Athene cunicularia hypugaea) change their migratory tendency from one year to the next at two sites in southern Arizona. We also evaluated the heritability of migratory decisions by using logistic regression to examine the association between the migratory tendency of burrowing owl parents and their offspring. The probability of migrating decreased with age in both sexes and adult males were less migratory than females. Individual owls sometimes changed their migratory tendency from one year to the next, but changes were one-directional: adults that were residents during winter 2004–2005 remained residents the following winter, but 47% of adults that were migrants in winter 2004–2005 became residents the following winter. We found no evidence for an association between the migratory tendency of hatch-year owls and their male or female parents. Migratory tendency of hatch-year owls did not differ between years, study sites or sexes or vary by hatching date. Experimental provision of supplemental food did not affect these relationships. All of our results suggest that heritability of migratory tendency in burrowing owls is low, and that intraspecific variation in migratory tendency is likely due to: (1) environmental factors, or (2) a combination of environmental factors and non-additive genetic variation. The fact that an individual’s migratory tendency can change across years implies that widespread anthropogenic changes (i.e., climate change or changes in land use) could potentially cause widespread changes in the migratory tendency of birds.     

Gulls can change their migratory behavior during lifetime

Migration is a widespread phenomenon among birds and is likely to be subject to strong selective pressures. Birds' annual routines and behaviors might be expected to change during their different life history stages, resulting in different, age‐related migration patterns. However, although migration has been the subject of many publications, age‐related differences in migration have received little attention. The present study examined age‐related changes in individual migration habits in lesser black‐backed gulls, Larus fuscus. We analyzed data from 10‐year (1998–2007) color‐ringing project in NW England, comprising more than 10 000 ringed individuals. Our results showed a latitudinal cline in age structure across the wintering range, with adults and gulls in their first breeding year wintering closer to the breeding grounds. Supporting this result we observed that individuals, as they get older, changed the migration behavior and winter closer to the breeding areas. Interestingly, we found no differences in survival rates across the wintering grounds. Thus differences in survival rates can not account for the latitudinal cline in age structure, and the observed findings seem to be best explained by the arrival time hypothesis, based on a mechanism whereby individuals are able to change their migratory behavior as result of the onset of sexual maturity and associated mating pressures.     

Kinship and social bonds in female chimpanzees (Pan troglodytes)

A large body of theoretical and empirical research suggests that kinship influences the development and maintenance of social bonds among group‐living female mammals, and that human females may be unusual in the extent to which individuals form differentiated social relationships with nonrelatives. Here we combine behavioral observations of party association, spatial proximity, grooming, and space use with extensive molecular genetic analyses to determine whether female chimpanzees form strong social bonds with unrelated individuals of the same sex. We compare our results with those obtained from male chimpanzees who live in the same community and have been shown to form strong social bonds with each other. We demonstrate that party association is as good a predictor of spatial proximity and grooming in females as it is in males, that the highest party association indices are consistently found between female dyads, that the sexes do not differ in the long‐term stability of their party association patterns, and that these results cannot be explained as a by‐product of the tendency of females to selectively range in particular areas of the territory. We also show that close kin (i.e. mother–daughter and sibling dyads) are very rare, indicating that the vast majority of female dyads that form strong social bonds are not closely related. Additional analyses reveal that “subgroups” of females, consisting of individuals who frequently associate with one another in similar areas of the territory, do not consist of relatives. This suggests that a passive form of kin‐biased dispersal, involving the differential migration of females from neighboring communities into subgroups, was also unlikely to be occurring. These results show that, as in males, kinship plays a limited role in structuring the intrasexual social relationships of female chimpanzees. Am. J. Primatol. 71:840–851, 2009. © 2009 Wiley‐Liss, Inc.     

Correlates of alternative migratory strategies in western bluebirds

Partial migration occurs when only some animals in a population migrate. While evidence suggests that migratory strategies are partially controlled by genes, individual and environmental conditions which alter the cost‐benefit trade‐off of migration among individuals are also likely to play a role. Three hypotheses have been advanced to explain condition‐dependent partial migration: the arrival time, dominance and body size hypotheses. In this study, we asked whether these hypotheses explained differences in migratory strategy among individuals in a partially migratory population of western bluebirds Sialia mexicana breeding in southern British Columbia, Canada. We used stable hydrogen isotope signatures in claw tissue to determine migratory strategy of individual bluebirds, and examined patterns of migration at both individual and population levels. The proportion of resident bluebirds varied significantly over the three years of the study, and across study sites. Several migrants switched to the resident strategy between years; however, we found no evidence of strategy switching in the opposite direction. Young birds were significantly more likely to be resident than older birds, a pattern which could arise if early arrival is particularly important for birds obtaining a territory for the first time. Furthermore, young females were the most likely of all sex–age classes to be resident, which may reflect a survival advantage of residency for young females. Finally, birds mated assortatively by migratory strategy and isotopic evidence suggests that members of a pair often wintered in the same place. Our results provided no support for the dominance or body size hypotheses, and only limited support for the arrival time hypothesis in bluebirds. However, taken together, we suggest that our findings indicate that social factors may influence migratory strategies in this system.     

Effects of body size on sex‐related migration vary between two closely related gull species with similar size dimorphism

Studies of migration have revealed multiple trade‐offs with other life‐history traits that may underlie observed variation in migratory properties among ages and sexes. To assess whether, and to what extent, body size and/or sex‐specific differences in competition for resources (e.g. breeding territories or winter food) may shape variation in migration distance and timing of arrival in ecologically and phylogenetically related species, we combined over 30 000 sightings of individually marked, sexually mature males and females of Herring Gulls Larus argentatus and Lesser Black‐Backed Gulls Larus fuscus with biometric measurements and phenological observations at a mixed breeding colony. In L. argentatus, larger males migrated further from the breeding colony, whereas migration distance was independent of body size in adult females. In L. fuscus, no relationship between body size and migration distance was apparent in either sex. Mean arrival dates at the breeding colony did not vary with migration distances but differed between males and females of L. argentatus (but not L. fuscus). As allometry at least partly explains sexual segregation in migration behaviour in L. argentatus, but not in L. fuscus, we conclude that the effect of body size on sex‐related migratory strategies may vary between closely related, sympatric species despite similar size dimorphism.     

Differential timing of spring passage of Ruby‐throated Hummingbirds along the northern coast of the Gulf of Mexico

ABSTRACT Hummingbird migration has long fascinated researchers due to the limitations of small body size and high metabolic rate on migratory performance. Yet, few data are available concerning hummingbird migration strategies, especially for species that must negotiate major geographic barriers. To address this problem, we investigated the migration ecology of Ruby‐throated Hummingbirds (Archilochus colubris) passing through a coastal banding station in southwest Louisiana following flights across the Gulf of Mexico. Our aims were to describe the phenology of spring migration and explore potential differences in the migration ecology of males and females. During our 10‐yr study (1998–2007), we found that peak hummingbird passage generally occurred in the second half of April and that males preceded females by about three days. However, females arrived in significantly better energetic condition as measured by fat and muscle stores as well as size‐corrected body mass. Most birds did not stay at our study site to refuel, only 2% of individually marked birds were recaptured more than a day after initial capture (range = 1–5 d). Our results suggest that Ruby‐throated Hummingbirds exhibit protandrous migration (i.e., males migrate earlier) and that en route body condition may be a consequence of sexual dimorphism in wing morphology (i.e., lower wing loading in females) that allows females to expend less energy during migration across the Gulf of Mexico.     

What triggers facultative winter migration of Great Bustard (Otis tarda) in Central Europe?

The Great Bustard is on the brink of extinction in Central Europe. Its population is known to suffer high mortality during hard winters, particularly when severe weather conditions cause migration. Long-term winter food management in two populations in Germany did not prevent migration events. To identify migration-triggering factors we tested the potential influence of snow, temperature, phase of winter and development of a tradition of migration. Comparing migratory behaviour with long-term local weather records, we found that snow cover is a much stronger trigger for migration than frost and low temperatures. We conclude that snow heavily affects the Great Bustard’s energy balance mediated not only by limited food access but also by the particular properties of its plumage. This could explain migration events despite food availability and is consistent with our results concerning a tendency for females to undertake facultative winter migration more than males. Available data are currently insufficient to confirm or reject the idea that Great Bustard populations develop a tradition of migratory behaviour following a previous winter migration, and we found no evidence for a decrease in the disposition of the Great Bustard to migrate during the course of winter.     

Migration phenology and winter habitat quality are related to circulating androgen in a long‐distance migratory bird

In migratory birds, the timing of departure from wintering grounds is often dependant on the quality of habitat on an individual's territory and may influence individual fitness, resulting in an interaction of life history stages across large geographical distances. American redstart Setophaga ruticilla males who overwinter in high quality habitats arrive early to breed and subsequently produce more offspring than late arrivers. Since many migratory species overlap vernal migration with the physiological transition to breeding, we examined if breeding preparation plays a role in this seasonal interaction. We tested the hypothesis that early arriving male redstarts from high quality winter habitats are in superior breeding condition by simultaneously measuring winter habitat quality (stable‐carbon isotopes) and breeding preparation (circulating androgen, cloacal protuberance (CP) diameter) upon arrival at breeding grounds. Compared with late arrivers, early arriving males were from higher quality winter habitats and had higher androgen, but smaller CPs. Males arriving with higher androgen were in more advanced physiological migratory condition, as measured by haematocrit. Early arrivers were more likely to successfully breed, but there was no significant relationship between androgen upon arrival and breeding success. One possible explanation for these relationships is that androgen measured during arrival is most relevant in a migratory context, such that birds with high androgen may benefit from effects on migratory condition, positively influencing fitness through earlier arrival.     

Social organization of white‐headed langurs (Trachypithecus leucocephalus) in the Nongguan Karst Hills,Guangxi, China

The number of males per group is the most variable aspect of primate social organization and is often related to the monopolizability of females, which is mainly determined by the number of females per group and their reproductive synchrony. Colobines show both inter‐specific and intra‐specific variations in the number of males per group. Compared with other colobine species, little is known about the social organization of white‐headed langur (Trachypithecus leucocephalus), despite its endangered status and unusual limestone habitat. As a part of a long‐term study of the white‐headed langurs in the Nongguan Karst Hills, Guangxi, China, we quantitatively investigated their social organization by analyzing census data from 1998 to 2003. The population censuses revealed that the predominant social organization of bisexual groups was the one‐male group, similar to a previous report on this species and many other Asian colobines. In such groups, one adult male associated with 5.1 adult females, 0.1 sub‐adult males, 2.6 juveniles and 2.9 infants on average, with a mean group size of 11.7 individuals. In addition, three multi‐male groups were recorded, consisting of 2–3 adult males, 1–5 adult females, 0–2 sub‐adult males, 0–7 juveniles and 0–2 infants. They did not contain more adult females than the one‐male groups and were unstable in group membership. The langurs outside bisexual groups were organized into small nonreproductive groups or lived as solitaries. The nonreproductive groups averaged 1.3 adult males, 1.3 sub‐adult males and 2.6 juveniles. Juvenile females were present in such groups on 52.4% of all occasions. As predicted by the monopolization model, the prevalence of the one‐male pattern in this species may mainly be attributed to the small number of females in the group. The possible reasons for the occurrence of multi‐male groups and the presence of juvenile females in nonreproductive groups are also discussed. Am. J. Primatol. 71:206–213, 2009. © 2008 Wiley‐Liss, Inc.     

Mate‐choice copying: A fitness‐enhancing behavior that evolves by indirect selection

A spatially explicit, individual‐based simulation model is used to study the spread of an allele for mate‐choice copying (MCC) through horizontal cultural transmission when female innate preferences do or do not coevolve with a male viability‐increasing trait. Evolution of MCC is unlikely when innate female preferences coevolve with the trait, as copier females cannot express a higher preference than noncopier females for high‐fitness males. However, if a genetic polymorphism for innate preference persists in the population, MCC can evolve by indirect selection through hitchhiking: the copying allele hitchhikes on the male trait. MCC can be an adaptive behavior—that is, a behavior that increases a population's average fitness relative to populations without MCC—even though the copying allele itself may be neutral or mildly deleterious.