An experimental test of hypotheses explaining social segregation in dimorphic ungulates

Michelena, Pablo; Bouquet, Pierre Marie; Dissac, Agnes; Fourcassié, Vincent; Lauga, J.; Gérard, Jean‐François; Bon, Richard

doi:10.1016/j.anbehav.2004.04.008

Cited by 52 publications

(35 citation statements)

References 39 publications

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“…We previously observed a group containing 15 adults of both sexes for 7 weeks. While grazing, merinos congregated in a very small surface area, which may reflect strong inter-individual attraction of sheep, limiting spreading of the group (Michelena et al, 2004). With respect to that study, we also note that individual distances were close to the individual distance measured in the present experiment (see also Michelena, 2001).…”

Section: Discussionsupporting

confidence: 83%

“…The stability of the mixed-sex groups might be explained by a similar level of attraction of both sexes for females. However, we also found that pairs of sheep of the same sex were more frequent than expected (Michelena et al, 2004). Social discrimination of males, as reflected by inter-individual distance, is one factor that may have played a role in this social segregation on a small scale.…”

Section: Discussionsupporting

confidence: 53%

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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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Section: Discussionsupporting

confidence: 83%

Section: Discussionsupporting

confidence: 53%

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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“…Our study was not designed to assess the effect of asynchrony on group splitting. However, the difference in synchrony between female and mixed-sex groups is moderate, and it seems to be insufficient to induce splitting in mixed-sex groups of merino sheep (see Michelena et al 2004). This does not mean that the activity budget hypothesis, or at least the assumption that increasing dimorphism in body mass is correlated with differences in activity budget, is unfounded.…”

Section: Discussionmentioning

confidence: 99%

“…They display a relatively high level of sexual dimorphism, are easier to manage than wild sheep and groups of same-sex and mixed-sex groups can easily be formed and observed under controlled conditions. In a previous experiment, Michelena et al (2004) found that 15 males and 15 females of dimorphic sheep (body mass ratio: 1.5) introduced simultaneously into 1-ha paddocks remained spontaneously in a single mixed-sex group. Rams and ewes within this group did not differ in time spent inactive.…”

Section: Introductionmentioning

confidence: 95%

“…Although experimental studies cannot account for all of the components observed in free-ranging populations (Bowyer 2004), they nonetheless enable different hypotheses to be tested. Studies of sexual differences in activity budget and synchrony according to age-sex categories and their relationship to group cohesion under controlled conditions are scarce (Pe´rez-Barberı´a and Gordon 1999a; Michelena et al 2004).…”

Section: Introductionmentioning

confidence: 99%

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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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The effects of castration, sex ratio and population density on social segregation and habitat use in Soay sheep

Ruckstuhl

Manica

MacColl

et al. 2005

Behav Ecol Sociobiol

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An experimental test of hypotheses explaining social segregation in dimorphic ungulates

Cited by 52 publications

References 39 publications

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

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

Sexual dimorphism, activity budget and synchrony in groups of sheep

The effects of castration, sex ratio and population density on social segregation and habitat use in Soay sheep

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