Sex, Rank and Age Differences in the Japanese Macaque (Macaca fuscata yakui) Participation in Inter-Group Encounters

In many species interactions among group are often characterized by agonistic behaviour. Although animals may participate in inter‐group encounters in different ways, depending on their energetic requirements, reproductive tactics, and/or developmental stage, the proximate causes affecting an animal's participation in inter‐group encounters are still poorly understood. Indeed, many studies have analysed the behaviour of males and females during inter‐group encounters without considering the importance of additional factors (e.g. rank). This study focuses on wild non‐provisioned Japanese macaques (Macaca fuscata yakui) living on Yakushima Island, Japan. It aims to determine how monkeys of different sex, age, and rank behave during inter‐group encounters and it discusses the implications and consequences of their behaviour on group composition and male dispersal. Males participated significantly more than females in inter‐group encounters, by displaying more aggressive or affiliative behaviour. High‐ranking and/or adult males were more aggressive than low‐ranking and/or subadult males during encounters occurring in the mating season and they also showed more herding behaviour. This trend was not found in inter‐group encounters occurring during the non‐mating season. Finally, males which then emigrated to new groups were low‐ranking and/or subadult individuals. Those males displayed more affiliative behaviour towards foreign males than males which did emigrate. These data indicate that in non‐territorial species with male dominance over female and high competition for mating partners males play an active, and often aggressive, role during inter‐group encounter while female participation is scarce. Factors such as age, rank and period of the year (in seasonally breeding species) have to be taken into considerations when analysing interactions between groups and their effects on group composition and social behaviour.     

Inter-male aggression in relation to female availability and residence status in corn mice <Emphasis Type="Italic">Calomys musculinus</Emphasis>

We conducted an experimental study to test the hypothesis that, at low female availability, males show intrasexual aggressive behaviour and home range owners are more aggressive than home range intruders. Using field dyadic arena test, we carried out 35 male–male trials in four 0.25 ha enclosures, two male-biased (experimental enclosures) and two unbiased (control enclosures). Dyadic encounters were conducted between unrelated and sexually mature males of similar weight and age which established home ranges in the same enclosure at the same trapping session. Each inter-male encounter was performed in the home range of one of the opponents between the home range owner and a home range intruder. When sex ratios were male-biased, inter-male amicable behaviour was absent and we found significant rates of inter-male aggressiveness, being home range owners much more aggressive than intruders. In the unbiased enclosures, inter-male encounters resulted mainly in noninteractive or amicable interactions. We found that inter-male aggression varied in relation to female availability being more evident in home range owners.     

Structural complexity of territories: preference, use of space and defence in commensal house mice, Mus domesticus

Previous studies suggest the physical structure of a habitat has profound effects on intraspecific competition and spacing behaviour among small mammals. We compared habitat preferences and the exploratory behaviour and aggressive territorial defence of male house mice in three types of enclosure differing only in their degree of structural complexity. Each enclosure contained a nestbox placed in one corner, a central food hopper and 10 house bricks. The bricks were either placed around the outer walls (open enclosures), lined up across the middle (wall enclosures) or scattered separately across the floor (complex enclosures). In pairwise choice tests, mice showed a strong preference for wall or complex enclosures over open enclosures but no preference between wall and complex enclosures. They were more active throughout the enclosure with complex structuring and stayed near the side walls in open enclosures. Residents in open enclosures initially showed a lower rate of attack and duration of pursuit when faced with an intruder but not when faced with a second intruder. In complex enclosures, nearly all encounters ended because the residents continued pursuit but lost track of the intruder. This occurred in only half of intruder pursuits in open and wall enclosures. Our results suggest that mice prefer areas containing physical structure because this provides a degree of protection from predators but territories with complex physical structuring appear to be much more difficult to defend. Complex areas may thus support a higher density of mice than open areas or those with more simply aligned physical structuring. Copyright 2000 The Association for the Study of Animal Behaviour.     

Social Dominance among Male Meadow Voles is Inversely Related to Reproductive Success

Intrasexual selection can occur through direct aggressive interactions between males for access to females. We tested the relationship between social dominance and male reproductive success among meadow voles, Microtus pennsylvanicus. Dominance ranks of wild‐caught males were determined using neutral arena trials, with the winner of two of three trials considered dominant. These males were then released into field enclosures and allowed to visit females housed in nestboxes for 8 wk, and males’ home range sizes were determined using weekly grid trapping. Male reproductive success was determined using molecular paternity analysis (six microsatellite primers) for all pups born during the field experiment. Males with higher dominance ranks had larger home ranges. However, male dominance rank was not predictive of the number of total visits to females’ nestboxes or the number of visits to each male's most frequently visited nestbox. Males that made more visits to nestboxes sired more litters. Males that had higher dominance ranks sired fewer litters. These results suggest that there is a reproductive disadvantage to having higher dominance rank among male meadow voles.     

The significance of chelae in the agonistic behaviour of the white‐clawed crayfish,a Ustropotamobius pallipes

As in other benthic decapods, crayfish have chelae that are important for intra‐specific agonistic encounters. In Austropotamobius pallipes, scars and mutilations are present mostly on the chelae, these being the main targets of agonistic contacts. Because males participate in more aggressive interactions than females do and compete with other males for acquiring females in escalating contests, selection for large chelae should be stronger in males. Thus, in A. pallipes (i) chelae are longer, wider and higher in males than in females; (ii) chelar size in males increases allometrically with cephalothorax length; (iii) male specimens are more often deprived of at least one cheliped and (iv) large males have the highest frequency of scars. Males with one regenerated cheliped, when opposed to a competitor with both large chelipeds, display the same motivation to fight, but perform less chelae threat displays than normal crayfish and immediately get a lower hierarchical rank. In these contests, Resource Holding Potential (= chelar size) is highly different between the crayfish and the information of this asymmetry is correctly transferred between the two opponents.     

Alloparental Responsiveness to Newborns by Nonreproductive,Adult Male,Common Marmosets (Callithrix jacchus)

Parental care in mammals is influenced by sensory stimuli from infants, and by changes in the hormone levels of caretakers. To determine the responsiveness to infant cues in nonreproductive adult male common marmosets (Callithrix jacchus) with and without previous experience in caretaking, we exposed 12 males to newborn marmosets and assessed their cortisol plasma levels and behavioral response. Newborn marmosets housed in transparent enclosures were placed inside the cages of the adult male subjects. Males were exposed four times to two different experimental conditions: (a) newborn enclosures remained closed during the observation period and (b) newborn enclosures were opened during the observation period to allow direct social interaction by the adult males. Blood samples from adult males were collected after each behavioral observation trial to measure the levels of cortisol. The behavioral responses of adult males exposed to the closed and open newborn enclosures showed a significant difference only with respect to the frequency of displacements, where males moved among the quadrants of their own cages with greater frequency when the newborn enclosure was sealed. Experienced males approached newborn enclosures more frequently, spent more time in close proximity, and carried and recovered newborns more quickly than inexperienced males. The successive exposure to newborns increased the responsiveness in inexperienced males. The highest levels of plasma cortisol in adult males were recorded following periods of exposure to the sealed newborn enclosures. This suggests that successive exposure to newborns and previous alloparental caregiving experience while living in family groups influences the responsiveness of male marmosets to the sensory cues of newborns. Am. J. Primatol. 75:145‐152, 2013. © 2012 Wiley Periodicals, Inc.     

The Function of the Four Types of Waving Display in Uca lactea: Effects of Audience,Sand Structure,and Body Size

Multiple signals that convey different messages have been reported in many taxa, but relatively few studies have been made on such signals in invertebrates. In the present study, I investigated four types of claw‐waving display used in the fiddler crab Uca lactea to test whether the displays have different functions. Three males with a sand structure beside their burrows (which can attract females) and three males without a sand structure were fenced in an opaque enclosure, and I videotaped their waving displays after releasing two burrowless males or two burrowless females to test the effects of audiences. (a) Lateral‐circular waving tended to occur in enclosures with burrowless females and was performed frequently by males that had sand structures. (b) Lateral‐flick waving was performed frequently by males without sand structures, and its frequency was positively correlated with the signaler’s body size. (c) Rapid‐vertical waving was observed frequently in enclosures with burrowless males, and its frequency was negatively correlated with the signaler’s body size. (d) Circular waving tended to occur in enclosures with burrowless females and was performed frequently by males that had sand structures, and its frequency was positively correlated with the signaler’s body size. In my previous study, lateral‐circular waving was often seen in the breeding season and was mostly performed to female audiences, lateral‐flick waving was frequently performed to neighboring resident males, rapid‐vertical waving was performed mainly to intruding burrowless males, and circular waving did not have apparent audiences in most cases. Finally, I concluded that lateral‐circular waving was used as a courtship display, lateral‐flick waving was related to border disputes, rapid‐vertical waving was used for burrow guarding, and circular waving was used to broadcast the signaler’s general quality.     

The Effects of Predation Risk, Food Abundance, and Population Size on Group Size of Brown-Headed Cowbirds (Molothrus ater)

Social and ecological conditions can influence flock formation (e.g. number of flocks, flock size, etc.) depending on the degree of social attraction of a species. We studied group formation in brown‐headed cowbirds (Molothrus ater) over short time periods (30 min) in two semi‐natural experiments conducted under controlled conditions. First, we determined the shape of the relationship between intake rate and flock size by manipulating group size in a single enclosure. Second, we assessed the role of population size, food abundance, and predation risk, and their interactions, in flock size formation in a system of four enclosures (two with and two without food) connected to a central refuge patch. In the first experiment, we found that pecking rates peaked at intermediate flock sizes (three to six individuals), which was influenced by greater availability of foraging time and more aggressive interactions in large groups. In the second experiment, flock sizes in the patches with food increased with population size likely due to the benefits of patch exploitation in groups. Flock size decreased after predator attack probably because refuge availability reduced perceived predation risk more than flocking in larger groups. Food abundance had minor effects, varying flock sizes between the two patches with food, under high food availability conditions when population size was high, probably due to social cohesion effects. Our results suggest that: (1) this species has an inverted‐U food intake–group size relationship with a range of intake‐maximizing flock sizes rather than a single peak, (2) the presence of a near refuge modifies the expected benefits of group patch exploitation under high predation risk, and (3) an increase in population size would more likely be translated into rapid increases in the size of the flocks rather than in more new flocks.     

Male Reproductive Success in a Social Group of Urban Feral Cats (Felis catus L.)

Dominance rank, morphological characteristics and reproductive success of adult males were measured in a multi‐male multi‐female group of urban feral cats (Felis catus L.). Paternity of nine litters (34 kittens) of the domestic cat from six females was determined through microsatellites analyses at nine loci. The percentage of multiple paternities in this social group was as high as 78%. A positive correlation was found between male size/body weight and dominance. The males who sired the highest number of kittens were the dominant ones. Additionally, dominant males were more likely to be infected by the feline immunodeficiency virus, a virus transmitted by bites through aggressive interactions. Thus this study demonstrates that rank and body weight were both important in predicting the annual reproductive success. However, it shows that the reproductive benefit associated to rank may be balanced by cost due to at‐risk aggressive behaviour of dominant males.     

Social rank and body size as determinants of positional behavior inPan troglodytes

A yearlong study of the positional behavior ofPan troglodytes at the Mahale Mountains National Park yielded 571 hr of observation.Cant (1987) articulated four predictions concerning the relationship between body weight/branch diameter and positional behavior based on the classic suspensory-ape paradigm. He noted that only two were supported by orangutan data. Three of these four hypothesis were not supported by chimpanzee data, as follows: there was no significant difference between the three largest males and the four smallest males in (1) branch diameters (5.8 cm vs 5.2 cm) nor (2) in the percentage of arm-hanging (13.6% vs 12.1%); and (3) large males did not arm-hang significantly more often than small males in any of three support diameter categories. The fourth hypothesis, that arm-hanging should be more common among smaller branches, was supported: arm-hanging as a percentage of all posture rose from 2.5% to 8.3% to 24% as stratum size decreased from >10 cm to <3 cm. The possibility that the first three hypotheses failed because of confounding effects of a correlation between body size and social rank was examined. Multiple regressions were done on 6600 2-min instantaneous observations on focal individuals. With social rank effects factored out, larger individuals preferentially utilized smaller, rather than larger supports. When positional mode frequencies were compared between large and small males matched for social rank, large males exhibited a lower frequency of arm-hanging than small males. An unexpected result was that social rank more consistently predicted branch diameter choice than body size. The most profound trend was for high ranking males to use larger supports, even though they spent more time in the terminal branches. These results suggest that (1) suspensory behavior is functionally related to small branch diameters; (2) chimpanzees do not prefer smaller branches, rather they are forced into them by food choice limitations; and (3) social rank more profoundly affects chimpanzee behavior than body weight.     

Ontogenie und Funktion der Rangordnung innerhalb einer Geschwisterschar von Graugänsen (Anser anser L.)

Between the siblings of a family of greylag geese (Anser anser L.) a rank order is established by fighting during the first days after hatching, and also by other, more complex interactions. The position of each goose in the rank order can be defined by three groups of behaviour patterns (aggressive behaviour, “greetings”, escape responses). A clear-cut ranking relation between two individuals is a prerequisite for their close cohesion. The survival function of rank order lies in diminishing the intensity and frequency of agonistic interactions, in diminishing social stress situations and in guaranteeing the close family cohesion.     

Homogeneously sized groups increase aggressive interaction and affect social stress in Thai strain Nile tilapia (Oreochromis niloticus)

Social fish raised in farms are usually kept in groups of similar-sized individuals. However, social animals of similar size typically have similar fighting ability, which increases aggressive interaction for social rank establishment, as well as social stress. We compared Thai strain Nile tilapia fish, Oreochromis niloticus (L.), held under two treatments: (1) The Homogeneous one, with five adult male fish of similar size and (2) the Heterogeneous treatment with five adult males of different sizes. We recorded the frequency of aggressive interactions and checked social stability and stress levels (cortisol) after five days in the groups. Grouping similar sized Thai Nile tilapia increased the aggressive interactions and delayed rank stability with increased body injuries as a consequence. Homogeneous-sized individuals showed a similar level of stress while heterogeneous-sized individuals showed different stress levels with dominants being more stressed than subordinates. The data indicate that the practice of selecting fish of similar size in aquaculture management could reduce the welfare of social fish and that the effect is observed in different lineages.     

Mating dominance amongst male Himalayan tahr: Blonds do better

In ungulates, rank order is determined by differences in weight, body size, weapon size and age. In the Caprini tribe (Bovidae: Caprinae), adult male Himalayan tahr are unique to show different coat colours, but no sexual dimorphism in weapons. A highly significant correlation between hair colour and rank order was found during the rut: males with a lighter coloured ruff dominated over darker ruffed ones, in both aggressive interactions and access to oestrus females. We studied colour-based dominance in relation to weight, age and testosterone levels, which establish the social rank in most ungulates. No differences in weight and testosterone concentrations were found between adult male colour classes, but males with paler ruffs were significantly younger than darker adult males. The distribution of physical traumas from fights confirmed that younger, lighter-coloured males had a higher rank than older, darker males, a pattern which is unusual amongst ungulates. Coat colour seems to work as a signal of rank in male-male aggressive interactions and it changes according to age, whereas the relevant physiological determinants deserve further research. Intrasexual male competition has not changed weapon size or shape in the Himalayan tahr, but ruff colours are apparently used to signal rank and dominance. Colour patterns of adult males may then be homologous to ritualised weapons, apparently being a unique feature of male tahr amongst mammals.     

Benefits and Costs of Dominance in the Angelfish Centropyge bicolor

Social groups are often structured by dominance hierarchies in which subordinates consistently defer to dominants. High‐ranking individuals benefit by gaining inequitable access to resources, and often achieve higher reproductive success; but may also suffer costs associated with maintaining dominance. We used a large‐scale field study to investigate the benefits and costs of dominance in the angelfish Centropyge bicolor, a sequential hermaphrodite. Each haremic group contains a single linear body size‐based hierarchy with the male being most dominant, followed by several females in descending size order. Compared to their subordinate females, dominant males clearly benefited from disproportionately high spawning frequencies, but bore costs in lower foraging rates and greater aggressive defence of their large territories. Within the female hierarchy, more dominant individuals benefited from higher spawning frequencies and larger home ranges, but displayed neither higher foraging rates nor spawn order priority. However, dominance in females was also linked to aggressiveness, particularly towards immediate subordinates, suggesting that females were using energetically costly aggression to maintain their high rank. We further showed by experimentally removing dominant females that the linear hierarchy was also a social queue, with subordinates growing to inherit higher rank with its attendant benefits and costs when dominants disappeared. We suggest that in C. bicolor, the primary benefit of high rank is increased reproductive success in terms of current spawning frequency and the prospect of inheriting the male position in the near future, which may be traded off against the cost of aggressively defending rank and territory.     

Individual variation in habitat use and growth of male and female brown trout

We examined variation in growth and habitat use of individually PIT‐tagged brown trout Salmo trutta in three stream enclosures, each divided into a fine substrate, deep pool habitat and a coarse substrate, shallow habitat. Habitat use and movements of individual fish were monitored continually by placing PIT detectors between habitats. All fish were measured and weighed biweekly over a three month period. There was no significant relationship between habitat use and initial body size, nor was there a consistent relationship between habitat use and densities of benthic macroinvertebrates or abundance of drifting invertebrates in the two habitats. Most habitat changes occurred at night, with activity peaks just prior to sunrise and after sunset. Trout used pools more at night than during the day. Within any given day, diurnal and nocturnal habitat use of individual fish varied little, with variation greater at night than during the day. Partial habitat segregation by sex was observed; only males used pools extensively during daytime, whereas males and females used riffles.
Growth rate was positively related to use of pools during daytime but not at night. Growth rate was also affected by enclosure, with growth rates being highest in the most downstream enclosure, which had the deepest pool (mean of 42 cm) and lowest in the most upstream enclosure, which had the shallowest pool (mean of 28 cm). A complete exchange of trout between the most upstream and downstream enclosure indicated that the enclosure effect was due to physical differences and not to individual fish differences between enclosures. The effect appears to have been caused by differences in depth as daytime use of pools was correlated with the area of the pool ≥35 cm deep, and production of trout biomass per enclosure was directly related to mean pool depth. Our results suggest that there is a relationship between habitat use and growth of individuals that is independent of body size, but that this relationship is influenced by sex of the fish and by the physical characteristics of the environment. Further, the data indicate that short‐term behavioral decisions on habitat use by brown trout have a potential effect on longer‐term individual fitness through growth rates.     

Dominance hierarchies among communally held juvenile lobsters,Homarus americanus

An investigation was conducted to determine the time for establishment of dominance hierarchies, their stability, and their relationship to molting and death of cultured juvenile lobsters, Homarus americanus. Agonistic displays between communally held animals were monitored daily. Interactions between all possible pairs of animals within each group were used to determine formation of a dominance hierarchy. A decrease in the frequency of agonistic interactions was recorded after the first day of the experiment. A stable four‐rank hierarchy was established within 2–3 days. When the dominant animal was molting, the subordinates displayed aggressively toward all members of the group but remained submissive to the dominant. When the dominant animal died, stability was lost and aggressive interactions among subordinates established a new ranking. Molting subordinates were highly susceptible to injury and death. Loss of subordinates did not affect the ranking of individuals.     

Agonistic Encounters Among Male Elephant Seals: Frequency, Context, and the Role of Female Preference

SYNOPSIS. Aggressive interactions between male northern elephantseals, Mirounga angustirostris, observed during the course ofthree breeding seasons are analyzed from the perspective ofcosts and benefits to individuals. Males spend less than onepercent of their time in aggressive activities and the overwhelmingmajority of agonistic interactions consist only of visual andvocal threats rather than physical combat. Males are most likelyto threaten other males when the likelihood that they will besuccessful in displacing the opponent is high. Males who aremounting females, or who are in close proximity to females,are threatened more frequently than males who are otherwiseoccupied. However, high ranking bulls do regularly issue threatswhich are not provoked by the location or behavior of the recipient.Despite the obvious costs of such threats, this behavior maybe favored as a result of female choice. Estrous females aremore receptive when mounted by a male who has just dominatedanother than when mounted by a male of similar rank who hasbeen resting or recently displaced by a stillmore dominant male. A general argument is made that in species where social statusof males is correlated with their genetic fitness, female choiceis likely to be based on social signals which are used incompetitionbetween males.     

A Young Manakin Knows His Place: Evidence for an Age‐Graded Dominance Hierarchy Among Long‐Tailed Manakins

In lek‐breeding systems where many males gather at display sites, males benefit from the establishment of dominance hierarchies to reduce intrasexual aggression and the associated risk of injuries. Long‐tailed manakins (Chiroxiphia linearis) exhibit an exploded lek‐breeding system wherein the two top‐ranking males at each display site team up to perform elaborate coordinated courtship displays for females. Young males undergo delayed plumage maturation whereby they acquire distinct pre‐definitive plumage patterns each year until they attain definitive plumage in their fifth year. This unique characteristic is thought to have evolved as a status‐signalling mechanism to aid in the establishment of an age‐graded dominance hierarchy in which older males are dominant to younger males. Previous research has shown evidence for such a dominance hierarchy among alpha and beta males; however, the presence of this hierarchy among males of other age classes has never been quantified. In this study, we investigated the presence of an age‐graded dominance hierarchy by determining whether older males direct more aggressive behaviours towards younger males. We also investigated whether status signalling is less clear within age classes than between age classes, by determining whether males within the same age class exhibit more aggression towards each other. We found that older males performed aggressive behaviours towards younger males much more frequently than younger males performed aggressive behaviours towards older males. We also found that some aggressive interactions occurred between males within the same age class more frequently than between males from different age classes. Our study provides some evidence for an age‐graded dominance hierarchy among male long‐tailed manakins of all age classes and also provides some support for the status‐signalling hypothesis. However, further research is needed to conclusively establish the presence of a linear dominance hierarchy among younger male manakins. This research may help us better understand the evolution of complex hierarchical systems in animals.     

Single Aggressive Interactions Increase Urinary Glucocorticoid Levels in Wild Male Chimpanzees

A basic premise in behavioural ecology is the cost-benefit arithmetic, which determines both behavioural decisions and evolutionary processes. Aggressive interactions can be costly on an energetic level, demanding increased energy or causing injuries, and on a psychological level, in the form of increased anxiety and damaged relationships between opponents. Here we used urinary glucocorticoid (uGC) levels to assess the costs of aggression in wild chimpanzees of Budongo Forest, Uganda. We collected 169 urine samples from nine adult male chimpanzees following 14 aggressive interactions (test condition) and 10 resting events (control condition). Subjects showed significantly higher uGC levels after single aggressive interactions compared to control conditions, likely for aggressors as well as victims. Higher ranking males had greater increases of uGC levels after aggression than lower ranking males. In contrast, uGC levels showed no significant change in relation to aggression length or intensity, indicating that psychological factors might have played a larger role than mere energetic expenditure. We concluded that aggressive behaviour is costly for both aggressors and victims and that costs seem poorly explained by energetic demands of the interaction. Our findings are relevant for studies of post-conflict interactions, since we provide evidence that both aggressors and victims experience a stress response to conflict.     

Individual success in mating balls of the grass snake, Natrix natrix: size is important

Natricine colubrid snakes, including the grass snake, Natrix natrix , are frequently involved in complex social behaviour during the reproductive season. During these social behaviours, several males may simultaneously court a single female, resulting in a 'ball'of mating snakes in which each male 'combats'with rival males by 'tail wrestling'(see Madsen & Shine, 1993). I performed some experiments in outdoor enclosures for testing the male-male competition and the determinants of mating success in male grass snakes involved in such 'ball'aggregations. I demonstrated that competition between males occurred both when a single female was available to multiple males and when two females were simultaneously available to males. The larger males achieved more copulations than the smaller ones, thus demonstrating that body size is a crucial determinant of the individual mating success. It was not clear which aspect of male body size is the most important in determining success in these mating 'balls', but it was evident that the age of the 'fighting'male was not correlated with mating success. Larger females attracted more males than smaller ones, both in the field and in the enclosure. Furthermore, when the size difference between available females in the cage was high, only the largest female was courted and coupled.