Grazing and vigilance by Soay sheep on Lundy island: Influence of group size, terrain and the distribution of vegetation

Hopewell, Lucy; Rossiter, RC; Blower, E.; Leaver, Lisa A.; Goto, Kazuhiro

doi:10.1016/j.beproc.2005.04.009

Cited by 39 publications

(23 citation statements)

References 28 publications

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“…Vigilance is a good indication of an animal's risk of predation and varies accordingly with body size, reproductive status, group size, and habitat characteristics (Mooring et al 2004). Vigilance is generally defined as time spent with the head raised during feeding periods (Whittingham et al 2004;Lung and Childress 2007) and plays a major role in the detection of predators (Hopewell et al 2005). This antipredator behaviour is widely used (Elgar 1989), potentially increasing fitness by decreasing the risk of mortality (Lima 1998;Watson et al 2007).…”

Section: Introductionmentioning

confidence: 99%

Vigilance and fright behaviour in the insular Svalbard reindeer (Rangifer tarandus platyrhynchus)

2011

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The insular Svalbard reindeer (Rangifer tarandus platyrhynchus Vrolik, 1829) provide an opportunity to study vigilance behaviour in the absence of predators and parasitizing insects. We measured vigilance and fright and flight response during summer 2006 in the Svalbard archipelago; in four areas on Nordenskiöld Land on the island Spitzbergen and in one area on the island Edgeøya. Vigilance was higher in reindeer on Edgeøya than in the four Spitzbergen areas. Males were less vigilant than lactating and barren females and vigilance decreased with increasing group size. The relaxed vigilance behaviour in Svalbard reindeer compared with wild reindeer in southern Norway demonstrates a vigilance threshold in the absence of traditional predators of Rangifer Hamilton Smith, 1827. Alert, flight initiation, and escape distances were all shorter in Adventdalen, with Longyearbyen and its considerably higher amounts of human activities and infrastructure than in the other study areas, supporting evidence of habituation towards humans. There were no systematic vigilance or differences in fright and flight responses between reindeer in Colesdalen, Reindalen, and Sassendalen, indicating that a combination of low level of human activities including hunting, recreation, and scientific activities affected the animals differently. Lower probability of assessing before fleeing in Edgeøya (63% vs. 94% in the Nordenskiöld Land areas), along with their higher vigilance, may indicate more frequent interactions with polar bears (Ursus maritimus Phipps, 1774) in Edgeøya.

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Section: Introductionmentioning

confidence: 99%

Vigilance and fright behaviour in the insular Svalbard reindeer (Rangifer tarandus platyrhynchus)

2011

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“…red deer Cervus elaphus ). Indeed, the Rum goats were often vigilant in the vicinity of red deer, highland cattle and ponies, a reaction also documented in the Soay sheep ( Ovis aries ) on Lundy Island (Hopewell et al. 2005).…”

Section: Discussionmentioning

confidence: 87%

“…Nonetheless, variation in vigilance with habitats might reflect the distribution of the forage and the particular characteristics of the vegetation in the four habitats. Forage distribution in the wet heath is more clumped than in the others (Gordon 1989), and thus individual goats might spend more time in a head up posture in order to locate food (Hopewell et al 2005). A more plausible alternative, however, is that competition among goats might vary among habitats (Shi & Dunbar 2006), and thus indirectly influence vigilance.…”

Section: Discussionmentioning

confidence: 99%

Group‐Size Effect on Vigilance and Foraging in a Predator‐Free Population of Feral Goats (Capra hircus) on the Isle of Rum, NW Scotland

2010

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Many previous studies have found that as group size increases, individual vigilance levels decrease and forage intake increases (group‐size effect), but few such studies have considered the impact of within‐group interactions and other confounding factors on the direction of group‐size effects. A free‐ranging population of feral goats (Capra hircus), with little predation threat, was studied on the Isle of Rum (northwest Scotland), from Jun. to Nov. 2000, to investigate the effects of group size on individual vigilance levels and foraging efficiency after taking into account the effect of confounding factors (e.g. sex, season, time of day, habitat, predation risk) and within‐group interactions (via changes in movement rates while feeding). Our results show that, while group size exerted a negative influence on individual vigilance levels and a positive effect on movement rate, foraging efficiency never increased with group size and even decreased at certain times of day. There was no sex difference in individual vigilance in feral goats, but foraging efficiency was higher in females than in males. Goats were more vigilant in fall than in summer. The results imply that the benefits for foraging obtained from the reduced vigilance level in larger groups may be constrained or offset by increased interaction (or competition) within larger groups even in a population that faces negligible predation risk.

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“…Sheep are gregarious animals and their grouping instinct is a protective mechanism as they are not equipped with the anatomical tools that allow them to fight predators effectively. Thus, increasing the number of individuals in the group increases also the opportunity for early detection and successful escape from a possible attack (Hopewell, Rossiter, Blower, Leaver, & Goto, ). Although in our study, sheep were not exposed to predation risk as the experimental area was wire‐fenced, they may have perceived themselves that they were under greater threat when they were grazing the grasses alone and not in a group.…”

Section: Discussionmentioning

confidence: 99%

Social network analysis of sheep grazing different plant functional groups

Yiakoulaki

Hasanagas

Michelaki

et al. 2018

Grass and Forage Science

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Social Network Analysis (SNA) is used for the first time to investigate the relations between plant functional groups and social structure of grazing sheep. The research was conducted on a grassland in Crete's island Lefka Ori, Greece during 2016. A flock of 20 sheep of Sfakion race was analysed as a network and the sheep as nodes. The focal sampling technique was applied during four experimental periods of four consecutive days × eight hours/day. The plant species selected by sheep during grazing were categorized into four functional groups (grasses, broad‐leaved forbs, shrubs and trees), and the proximity and conflict relations that were developed among the flock members were recorded. The tools of SNA were defined and interpreted in the sheep flock, and the Visone software is used to calculate the network variables of proximity and conflicts relations of nodes. Correlations between the plant functional groups and network variables were examined by Spearman's bivariate correlation test. Sheep collectivity was enhanced while grazing grasses and simultaneously, a tendency for hierarchization within the flock was identified. Similarly, the proximity of sheep increased during forbs’ grazing while their individualism was strengthened. When grazing shrubs, the proximity of sheep was only in part maintained while the grazing of trees seems as the most deconstructive forage option of sheep proximity relations. In general, the grazing of all plant functional groups decreases conflicts among sheep except that of trees, which was insignificant for developing such relations.

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Grazing and vigilance by Soay sheep on Lundy island: Influence of group size, terrain and the distribution of vegetation

Cited by 39 publications

References 28 publications

Vigilance and fright behaviour in the insular Svalbard reindeer (Rangifer tarandus platyrhynchus)

Vigilance and fright behaviour in the insular Svalbard reindeer (Rangifer tarandus platyrhynchus)

Group‐Size Effect on Vigilance and Foraging in a Predator‐Free Population of Feral Goats (Capra hircus) on the Isle of Rum, NW Scotland

Social network analysis of sheep grazing different plant functional groups

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