Sexual Segregation in Roosevelt Elk: Cropping Rates and Aggression in Mixed-Sex Groups

Weckerly, Floyd W.; Ricca, M. A.; Meyer, K. P.

doi:10.1093/jmammal/82.3.825

Cited by 26 publications

(43 citation statements)

References 23 publications

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“…The longer time spent feeding in mixed-sex groups may be related to a lower bite rate. The similar bite rate between sexes in mixed-sex groups is in accordance with the results found in the Roosevelt elk Cervus elaphus roosevelti (Weckerly et al 2001). However, male deer had lower cropping rates in single-sex than in mixed-sex groups while we found the opposite for merino males.…”

Section: Discussionsupporting

confidence: 89%

Sexual dimorphism, activity budget and synchrony in groups of sheep

et al. 2006

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The activity budget hypothesis has been proposed to explain the social segregation commonly observed in ungulate populations. This hypothesis suggests that differences in body size--i.e. between dimorphic males and females--may account for differences in activity budget. In particular, if females spend more time grazing and less time resting than males, activity synchrony would be reduced. Increased costs of maintaining synchrony despite differences in activity budget would facilitate group fragmentation and instability of mixed-sex groups. In this paper two prerequisites of the activity budget hypothesis were tested: (1) that males should spend less time feeding and more time resting than females in single-sex groups and (2) that lower activity synchrony should be observed in mixed-sex compared to single-sex groups. The activity budget and synchrony in mixed and single-sex groups of merino sheep (Ovis aries) of different sizes (2, 4, 6, 8 individuals) were measured in three contiguous 491-m2 arenas located in a natural pasture. Three same-size groups, one of each category, were observed simultaneously. We found no sexual differences in the time spent inactive and active (i.e. grazing, standing, moving, interacting). Males spent significantly more time grazing and less time standing than females. These differences disappeared when yearling males were omitted from the group. Males and females had similar bite and step rates. Sheep of both sexes spent less time resting and more time grazing and moving and had lower bite rates when in mixed-sex groups than when in single-sex groups. The synchrony among visually isolated groups was near zero, indicating that they changed activities independently. On the contrary, within-group synchrony was high; however it was higher in single-sex groups, in particular for males, than in mixed-sex groups. Our results suggest that differences in activity budget and synchrony alone are insufficient to explain social segregation.

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Section: Discussionsupporting

confidence: 89%

Sexual dimorphism, activity budget and synchrony in groups of sheep

et al. 2006

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“…Even during late gestation and especially lactation, when females might require as much food as males, they still require higher quality food because of their smaller body size. (3) The "social factors hypothesis", which postulates that social behaviour leads to sexual segregation, such as interactions with same-sex peers that facilitate the development of fighting skills, evaluation of potential rivals, and establishment of dominance relationships (Villaret and Bon 1995;Bon and Campan 1996;Cransac et al 1998;Le Pendu et al 2000;Bon et al 2001;Weckerly et al 2001). (4) The "activitybudget hypothesis", derived from the sexual dimorphismbody size hypothesis, which suggests that sexual segregation may be driven purely by differences in the activity budgets of adults of the two sexes because they differ in body size (Conradt 1998a(Conradt , 1998bRuckstuhl 1998Ruckstuhl , 1999Ruckstuhl and Neuhaus 2000, 2002 and not by sex differences in habitat requirements (Conradt 1999).…”

Section: Introductionmentioning

confidence: 99%

Relationship between predation-risk factors and sexual segregation in Dall's sheep (Ovis dalli dalli)

Corti¹,

Shackleton²

2002

Can. J. Zool.

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Using a population of Dall's sheep (Ovis dalli dalli), we examined two of the four main sexual-segregation hypotheses proposed: (1) the reproductive-strategy hypothesis, which proposes that males feed in the best foraging areas to enhance their reproductive fitness and females use areas with lower predation risk to raise offspring; and (2) the sexual dimorphism -body size hypothesis, which proposes that females use the areas with best forage to satisfy the nutritional demands of gestation and lactation, and that males, owing to their larger body size, have greater absolute metabolic requirements and therefore have to feed on forages which are more abundant but of lower quality. In our study, males were found farther from cover, in gentle terrain, and at lower altitude than were female groups, which were near cliffs or talus at higher altitudes. Female groups without lambs left cover, but were always active (feeding or moving). Forage density index values were higher in areas used by males than in areas used by female groups. Nutritional components were generally similar, but fibre content was higher in male areas. Signs of wolves (Canis lupus) and predation on Dall's sheep were recorded only at male areas. The results support the reproductivestrategy hypothesis, indicating that predation plays a key role in the development of sexual segregation in Dall's sheep.Résumé : Nous avons examiné, chez une population de mouflons de Dall (Ovis dalli dalli), deux des quatre principales hypothèses proposées pour expliquer la ségrégation sexuelle : (1) l'hypothèse de la stratégie reproductive qui veut que les mâles utilisent les meilleurs sites de recherche de nourriture pour augmenter leur fitness reproducteur, alors que les femelles choisissent des régions avec un plus faible risque de prédation pour l'élevage de leurs petits et (2) l'hypothèse du dimorphisme sexuel et de la taille du corps, selon laquelle les femelles utilisent les meilleurs sites de recherche de nourriture pour rencontrer les besoins nutritionnels imposés par la gestation et l'allaitement, alors que les mâles, qui ont des exigences métaboliques plus grandes à cause de leur taille plus importante, doivent se contenter de sources de nourriture qui sont plus abondantes, mais de qualité inférieure. Dans notre étude, les mâles se retrouvaient plus loin des zones de refuge, sur des terrains peu accidentés et à des altitudes plus basses que les groupes de femelles qui se tenaient près des falaises ou des talus à des altitudes plus élevées. Les groupes de femelles sans agneaux s'éloignaient des zones de refuge, mais elles étaient constamment actives (à manger ou à se déplacer). Les indices de densité du brout étaient plus élevés dans les zones utilisées par les mâles que dans les zones fréquentées par les groupes maternels. La composition nutritionnelle était en général semblable dans les deux zones, mais le contenu en fibres était plus grand dans les zones utilisées par les mâles. Les indications de la présence de loups (Canis lupus) et les incidents de prédatio...

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“…For example, group fusion could be dependent upon the capacity of individuals to discriminate the activity or the phenotype of conspecifics at a distance. Weckerly et al (2001) observed that Roosevelt elk Cervus elaphus roosevelti females avoid male groups exceeding six individuals. Bon and Campan (1996) proposed that social segregation between adults could result from social ontogeny -juvenile males being more motivated to interact than females using pseudo-sexual and agonistic-like interactions.…”

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confidence: 96%

An experimental study of social attraction and spacing between the sexes in sheep

Michelena

Henric

Angibault

et al. 2005

Journal of Experimental Biology

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Most ungulates are gregarious species and outside the mating season are typically observed in single-sex groups. However little is known about the mechanisms underlying social segregation between sexes. We investigated the effect of conspecific attraction on individual spacing between unrestrained merino sheep Ovis aries and confined conspecifics. We considered differences between males and females and whether attractiveness of the confined conspecifics depends on their sex. A series of binary choice experiments was conducted in a large outdoor arena, located in pastures. One or two stimulus animals were placed in small individual cages (1.5·mϫ ϫ1·m) on opposite sides of the arena. Sheep were tested with one fixed peer of the same or opposite sex vs an empty cage, and with two fixed peers of either the same sex as themselves, or one male and one female. Sheep in a control condition were exposed to two empty cages. In all of the test conditions, confined sheep were highly attractive. Males were more attracted by single stimulus peers of the same than the opposite sex, whereas females did not display such a preference. Sheep confronted with two restrained conspecifics tended to remain between the stimuli. This also occurred when the stimuli were of opposite sex, although the males tended to be located nearer the same-sex peer. Our findings can explain the strong aggregative behaviour of merino sheep, but also the social segregation previously observed in a mixed-sex group through higher attraction for same-sex than opposite-sex peers in males.

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Sexual Segregation in Roosevelt Elk: Cropping Rates and Aggression in Mixed-Sex Groups

Cited by 26 publications

References 23 publications

Sexual dimorphism, activity budget and synchrony in groups of sheep

Sexual dimorphism, activity budget and synchrony in groups of sheep

Relationship between predation-risk factors and sexual segregation in Dall's sheep (Ovis dalli dalli)

An experimental study of social attraction and spacing between the sexes in sheep

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