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1

Influences of sex, group size, and spatial position on vigilance behavior of Przewalski’s gazelles

100%
Shi J., Li D., Xiao W.
Acta Theriologica
|
2011
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tom 56
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nr 1
Group-living animals may need to spend less time being vigilant, consequently, having more time for other important activities such as foraging (i.e., group size effect). Przewalski’s gazelle (Procapra przewalskii) is a group-living social animal, and a study was conducted in Qinghai Province of China during June–August 2006 by using a continuous focal sampling method to investigate the influences of group size, sex, within-group spatial position, and nearest-neighbor distance on individual vigilance level (defined as scanning frequency per minute). Male gazelles were more vigilant than females. The gazelle’s vigilance level decreased with group size (group size effect), but only for females. The individuals at the central positions within a group were less vigilant than those at the peripheral positions, but the nearest-neighbor distance did not have any significant influence on the individual vigilance level. Our results support the hypotheses of group size effect and edge effects, but the sexual difference in vigilance level and in the response to group size effect on vigilance suggests that there may be sexual difference in the function and targets of vigilance behavior of Przewalski’s gazelles, which warrants more investigation, with incorporation of within-group spatial position, to better understand the mechanism underlying the group size effect and edge effect.
2

Grouping in roe deer: an effect of habitat openness or cover distribution?

100%
San J. C., Lovari S., Ferrari N.
Acta Theriologica
|
1997
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tom 42
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nr 2
Counts of roe deer Capreolus capreolus (Linnaeus, 1758) were conducted in the open fields of two reserves in Siena county (central Italy). Area A and area B were characterized by different indices of wood dispersion (0.8 and 1.6 respectively). Solitary roe deer were seen significantly more often in area B (open fields: 80%) than in area A (open fields: 48%). Males were significantly more solitary than females in both areas. Group size varied throughout the year, showing similar tendencies in both sexes and areas. The differences in deer concentration between areas appeared to depend on the distribution pattern of woodland more than proportion of open habitat.
3

Seasonal variation in group size of Cantabrian chamois in relation to escape terrain and food

84%
Perez-Barberia F. J., Nores C.
Acta Theriologica
|
1994
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tom 39
|
nr 3
The herd size of Cantabrian chamois Rupicapra pyrenaica parva (Cabrera, 1910) varied seasonally in relation to escape terrain and food availability in our study area (Asturias, north of Spain). The median group size of females without kids was 1 (mean ± SD = 1.62 ± 1.00), females with kids was 4 (5.59 ± 5.42), males was 1 (1.73 ± 1.78), and mixed group size was 7 (8.91 ± 7.91). The female-kid group size depended more on escape terrain availability than on food quality. Throughout the early weeks of the life of kids, the mothers remained in difficult access areas (cliffs and steep slopes), and showed a weak tendency to aggregate. These areas provided a wide visual range and hiding places for offspring and their use may be an anti-predation strategy. When the kids were able to run quickly, the mothers used subalpine meadows. These areas were very open and exposed kids to predation and human disturbance, however the forage has high nutritive value, and may compensate for the cost of breeding and suckling by the mothers. Aggregation may be selected as an anti-predation strategy in subalpine meadows, allowing a reduction in time spent vigilant by each individual in the group, and increased time available for other activities. The largest male groups were located in pastures with abundant but poor quality forage. Our results suggest that group size in Cantabrian chamois is very flexible, changing seasonally and in response to resource availability.
4

Predation risk, cover type, and group size in European rabbits in Donana [SW Spain]

84%
Villafuerte R., Moreno S.
Acta Theriologica
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1997
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tom 42
|
nr 2
As European rabbits Oryctolagus cuniculus (Linnaeus, 1758) in SW Spain face high prédation pressure, some antipredator tactics are expected. We examined rabbit group size in relation to the safety of the cover (sparse or dense), and the proximity to shrub cover. Stem density influenced the distance rabbits ventured from shrub; rabbits ventured greater distances when stem density in cover was higher. Rabbit group size was related to the distance to cover; solitary animals remained closer to protective cover, whereas rabbits in groups (> 3 animals) foraged further from cover. These results are consistent with the hypothesis that the formation of rabbit groups is related to defense against prédation, and that group size is influenced by risk of perception.
5

Composition, group size, and spatial distribution of European bison bulls in Bialowieza Forest

84%
Krasinska M., Krasinski Z. A.
Acta Theriologica
|
1995
|
tom 40
|
nr 1
European bison Bison bonasus (Linnaeus, 1758) bulls were observed in the Biało­wieża Primeval Forest between 1976 and 1990. During snow-free periods mean (± SD) group size was 1.63 ± 1.05. Mean group size in pre-rut was 1.83 ± 1.19 and was significantly (p < 0.001) larger than mean bull group size in rut 1.27 ± 0.63. Most often bulls were solitary (62.0%), small groups of up to 3 bulls were accounted in 32.2% of observations, and groups of 4-9 individuals in 5.8% of observations. In pre-rut period bulls active in reproduction (6-11 years old) secluded themselves from mixed groups; they lived solitary or in bull groups. Mean summer home range size of bulls over 4 yrs old was 2288.0 ± 696 ha. Mean monthly home range in pre-rut period was 963.3 ± 406.4 ha, i.e. significantly (p < 0.001) smaller than in rut (1662.0 ± 510.6 ha). In the snow-free season bulls mostly used fresh and moist deciduous forests (48.8% of encounters), and secondly mixed coniferous and mixed deciduous forests (28.9 and 19.1%). Bulls used tree stands more than 20 yrs old (54.3% of observations), but also open areas, i.e. young plantations up to 10 yrs of age, clearcuts and meadows (allto- gether 37.3% of observations). In winter, on an average 35% of adult bulls entered large mixed aggregations gathering near two supplementary feeding sites. The re­maining bulls took advantage of other feeding racks or enter farmland. Mean winter home range size of bulls was 426.1 ± 307 ha, and is significantly positively correlated to the animal age.
6

The effect of past and present group size on responses to prey in the ant Formica polyctena Forst

84%
Szczuka A., Godzinska E. J.
Acta Neurobiologiae Experimentalis
|
1997
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tom 57
|
nr 2
7

Group size: an important factor controlling the expression of predatory behaviour in workers of the wood ant Formica polyctena Forst.

84%
Szczuka A., Godzinska E. J.
Biological Bulletin of Poznań
|
2000
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tom 37
|
nr 1
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