Vigilance and fitness in grey partridges Perdix perdix: the effects of group size and foraging-vigilance trade-offs on predation mortality

1. Vigilance increases fitness by improving predator detection but at the expense of increasing starvation risk. We related variation in vigilance among 122 radio-tagged overwintering grey partridges Perdix perdix (L.) across 20 independent farmland sites in England to predation risk (sparrowhawk Accipiter nisus L., kill rate), use of alternative antipredation behaviours (grouping and use of cover) and survival. 2. Vigilance was significantly higher when individuals fed in smaller groups and in taller vegetation. In the covey period (in early winter when partridges are in flocks), vigilance and use of taller vegetation was significantly higher at sites with higher sparrowhawk predation risk, but tall vegetation was used less by larger groups. Individuals were constrained in reducing individual vigilance by group size and habitat choice because maximum group size was determined by overall density in the area during the covey period and by the formation of pairs at the end of the winter (pair period), when there was also a significant twofold increase in the use of tall cover. 3. Over the whole winter individual survival was higher in larger groups and was lower in the pair period. However, when controlling for group size, mean survival decreased as vigilance increased in the covey period. This result, along with vigilance being higher at sites with increasing with raptor risk, suggests individual vigilance increases arose to reduce short-term predation risk from raptors but led to long-term fitness decreases probably because high individual vigilance increased starvation risk or indicated longer exposure to predation. The effect of raptors on survival was less when there were large groups in open habitats, where individual partridges can probably both detect predators and feed efficiently. 4. Our study suggests that increasing partridge density and modifying habitat to remove the need for high individual vigilance may decrease partridge mortality. It demonstrates the general principle that antipredation behaviours may reduce fitness long-term via their effects on the starvation-predation risk trade-off, even though they decrease predation risk short-term, and that it may be ecological constraints, such as poor habitat (that lead to an antipredation behaviour compromising foraging), that cause mortality, rather than the proximate effect of an antipredation behaviour such as vigilance.     

普氏原羚的分布和种群数量调查

2003 年8 ～9 月,对青海省境内普氏原羚的分布和种群数量进行了专项调查。调查结果表明,普氏原羚现存7 个种群,累计数量为602 只;其中塔勒旋果种群属首次报道。与以往报道相比,目前元者和鸟岛种群数量呈下降趋势;海晏—刚察种群数量增长明显;湖东—克图种群数量有所回升,但仍没有达到20 世纪80 年代中期时的种群数量。普氏原羚种群数量变化与栖息地质量及人为干扰程度有密切相关。本次调查显示,普氏原羚现存栖息地呈不连续的间断分布,随着区域经济开发力度的加大,其栖息地在不断缩减、生存环境质量仍在继续恶化。     

Impact of increased predation risk on vigilance behaviour in a gregarious waterfowl,the Egyptian goose Alopochen aegyptiaca

Vigilance is amongst the most universal of anti‐predator strategies and commonly declines with increasing group size. We experimentally manipulated predation risk in a system with a known relationship between group size and vigilance levels to explore whether this relationship changes in response to elevated predation risk. We investigated the vigilance levels of Egyptian geese Alopochen aegyptiaca at eight golf courses in the western Cape, South Africa, to assess the perception of and reaction to predation risk. We manipulated predation risk by introducing trained Harris's hawks Parabuteo unicintus where avian predation was otherwise low or absent. The study confirmed the typical reduction in vigilance with group size on control sites, where the risk of predation is low. However, at experimental sites with elevated predation risk, a positive relationship between vigilance and group size was observed. We hypothesize that the mechanism for this relationship might be linked to social information transfer via copying behaviour and manipulation to induce vigilance. Thus, larger groups will have a higher probability of containing individuals with experience of elevated predation risk and their increased vigilance behaviour is copied by naïve individuals. This prediction is based on the intended outcome of introducing avian predation to make the geese feel less safe and to eventually leave the site as a management tool for controlling nuisance geese.     

On how risk and group size interact to influence vigilance

Vigilance allows animals to monitor their surroundings for signs of danger associated with predators or rivals. As vigilance is costly, models predict that it should increase when the risk posed by predators or rivals increases. In addition, vigilance is expected to decrease in larger groups that provide more safety against predators. Risk and group size are thus two key determinants of vigilance. Together, they could have additive or interactive effects. If risk and group size interacted, the magnitude of the group‐size effect on vigilance would vary depending on the level of risk experienced, implying that the benefits of sociality in terms of vigilance vary with risk. Depending on the model, vigilance is predicted to decrease more rapidly with group size at low risk or at high risk. Little work has focused directly on the interaction between risk and group size, making it difficult to understand under which conditions particular interactive effects arise and whether interactive effects are common in natural systems. I review the vast literature on vigilance in birds and mammals to assess whether interactive effects between risk and group size are common, and if present, which pattern occurs more frequently. In studies involving predation risk, the greatest proportion reported no statistically significant interactive effects. In other cases, vigilance decreased with group size more rapidly at low or high risk in a similar proportion of studies. In studies involving risk posed by rivals (social risk), most documented a more rapid decrease in vigilance with group size at low than at high risk, as predicted if the need to monitor rivals increases in larger groups. Low statistical power to detect interactive effects might have been an issue in several studies. The absence of interactive effects, on the other hand, might suggest constraints or limits on the ability of animals to adjust vigilance to current risk or group sizes. Interactive effects on vigilance have implications for the evolution of sociality and for our understanding of the phenotypic plasticity of predator‐ and competitor‐induced defences and deserve more attention in future studies.     

Effects of reproductive status, social rank, sex and group size on vigilance patterns in Przewalski's gazelle

Background

Quantifying vigilance and exploring the underlying mechanisms has been the subject of numerous studies. Less attention has focused on the complex interplay between contributing factors such as reproductive status, social rank, sex and group size. Reproductive status and social rank are of particular interest due to their association with mating behavior. Mating activities in rutting season may interfere with typical patterns of vigilance and possibly interact with social rank. In addition, balancing the tradeoff between vigilance and life maintenance may represent a challenge for gregarious ungulate species rutting under harsh winter conditions. We studied vigilance patterns in the endangered Przewalski''s gazelle (Procapra przewalskii) during both the rutting and non-rutting seasons to examine these issues.

Methodology/Principal Findings

Field observations were carried out with focal sampling during rutting and non-rutting season in 2008–2009. Results indicated a complex interplay between reproductive status, social rank, sex and group size in determining vigilance in this species. Vigilance decreased with group size in female but not in male gazelles. Males scanned more frequently and thus spent more time vigilant than females. Compared to non-rutting season, gazelles increased time spent scanning at the expense of bedding in rutting season. During the rutting season, territorial males spent a large proportion of time on rutting activities and were less vigilant than non-territorial males. Although territorial males may share collective risk detection with harem females, we suggest that they are probably more vulnerable to predation because they seemed reluctant to leave rut stands under threats.

Conclusions/Significance

Vigilance behavior in Przewalski''s gazelle was significantly affected by reproductive status, social rank, sex, group size and their complex interactions. These findings shed light on the mechanisms underlying vigilance patterns and the tradeoff between vigilance and other crucial activities.     

青海湖草原围栏对植物群落的影响兼论濒危动物普氏原羚的保护

青海省海晏县克图地区是我国特有动物普氏原羚 (Procapraprzewalskii)的主要分布地之一。我们于 2 0 0 1年 6月、7月和 8月在该地区开展了围栏内外植物群落的比较研究。围栏内无家畜放牧 ,主要草食野生动物为普氏原羚 ;围栏外为草食家畜放牧区。我们发现 ,自从 1999年建立草原围栏以后 ,围栏内外植物群落产生了明显差异 :(1)地上生物量。 6月份围栏外植物地上生物量显著低于围栏内 (df =39,p <0 .0 5 ) ;7、8月份围栏外植物地上生物量显著高于围栏内 (df=39,p <0 .0 5 )。 (2 )植物高度。 6月份围栏外的植物高度显著低于围栏内 (df =39,p <0 .0 5 ) ;7、8月份围栏外的植物高度与围栏内植物高度差异不显著 (df=39,p >0 .0 5 )。 (3)植物盖度。 6、7月份围栏外植物盖度显著低于围栏内 (df =19,p <0 .0 5 ) ;8月份围栏内外的植物盖度差异不显著 (df =19,p >0 .0 5 )。(4)牧草的比例。围栏外明显低于围栏内 (df =6 ,p <0 .0 5 ) ;围栏外非牧草的比例明显高于围栏内 (df =6 ,p <0 .0 5 )。 (5 )生物多样性。植物生长季节围栏外植物群落的生物多样性显著高于围栏内 (df =6 ,p <0 .0 5 )。在草原生态系统围栏内外植物群落研究结果比较的基础上 ,讨论了草食动物采食强度对草原生态系统植物群落影响和围栏与野生     

Dietary Overlap of Przewalski's Gazelle,Tibetan Gazelle,and Tibetan Sheep on the Qinghai-Tibet Plateau

Abstract: We studied food composition and overlap among sympatric Przewalski's gazelle (Procapra przewalskii), Tibetan gazelle (P. picticaudata), and Tibetan domestic sheep (Ovis aries) in the Upper Buha River, Qinghai-Tibet Plateau, using microscopic fecal analysis. The 2 gazelles forage mainly on plants from Leguminosae and Compositae families and domestic sheep feed mainly on Gramineae and Cyperaceae. The dietary overlap index between the 2 gazelles and Tibetan domestic sheep increased from 0.43 to 0.58 during the plant-growing period to 0.76–0.77 during the plant-withering period, which indicated competition for foods intensified during the food-limited season. Although the 2 gazelle ate similar diets, they might avoid food competition by occupying different foraging areas. We suggest reducing numbers of overwintering Tibetan domestic sheep on pastures to lessen survival pressure on the endangered gazelles during winters.     

Group size effect on vigilance: evidence from Tibetan gazelle in Upper Buha River, Qinghai-Tibet Plateau

Tibetan gazelle Procapra picticaudata is a threatened and endemic species to the Qinghai-Tibet Plateau. With the method of group scan sampling, we observed the behaviours of males and females of the gazelle in the two summers of 2005 and 2006, in order to test the group size effect on group vigilance. We found that male gazelles were significantly more vigilant than the females at both group scan level (percentage of individuals scanning during a session) and group scan frequency (percentage of intervals with at least one individual scanning). We also found a negative correlation between group scan level and group size and a positive correlation between group scan frequency and group size, showing the group size effect on vigilance was testified in Tibetan gazelle. The predation factor might be the main driving force for the group size effect.     

Relaxed predation theory: size,sex and brains matter

Australia's wildlife is being considerably impacted by introduced mammalian predators such as cats (Felis catus), dogs (Canis lupus familiaris), and foxes (Vulpes vulpes). This is often attributed to native wildlife being naïve to these introduced predators. A systematic review of the literature reveals that native metatherians (body mass range 0.02–25 kg) do not recognise, and show relaxed antipredator behaviours towards, native and some introduced mammalian predators. Native eutherians (all with body mass < 2 kg), however, do appear to recognise and exhibit antipredator behaviours towards both native and introduced predators. Based on our findings, we propose a novel theory, the ‘Relaxed Predation Theory’. Our new theory is based on the absence of large mammalian predators leading to reduced predation pressure in Australia during the past 40000–50000 years, and on three key differences between Australian metatherians and eutherians: size, sex, and brains. In light of this Relaxed Predation Theory, we make a number of recommendations for the conservation of Australian wildlife: (i) predator avoidance training of suitable species; (ii) exclusion fencing to exclude some, but not all, predators to facilitate the development of antipredator behaviours; (iii) captive breeding programs to prevent the extinction of some species; and (iv) reintroduction of Australia's larger predators, potentially to compete with and displace introduced predators. A more detailed understanding of the responses of Australian mammals to predators will hopefully contribute to the improved conservation of susceptible species.     

Sexual segregation in Tibetan gazelle: a test of the activity budget hypothesis

Tibetan gazelle Procapra picticaudata , a threatened endemic species on the Qinghai-Tibet Plateau, is a sexually dimorphic ungulate. Males are larger than females and both sexes live in different groups, except during the rutting season. In order to test the activity budget hypothesis, which was proposed to explain social segregation in ungulates, we studied the activity budget of male and female Tibetan gazelles during the summers of 2005 and 2006. The activity budget hypothesis predicts that females spend more time feeding and group members synchronize their activities more in the same-sex groups than in the mixed-sex groups. We found that females and males of Tibetan gazelle had different activity budgets; females spent significantly longer time feeding and comparably less time on other activities. Activity synchronization indexes between female groups and male groups were similar (female groups: 0.81±0.17, male groups: 0.80±0.19), whereas both of them were significantly higher than that of mixed-sex groups (0.58±0.29). These results suggest that although sexual segregation might be caused by multiple mechanisms, the activity budget hypothesis about sexual segregation is supported by our studies of Tibetan gazelle on the Qinghai-Tibet Plateau.     

Predator detection and avoidance by starlings under differing scenarios of predation risk

Practically all animals must find food while avoiding predators.An individual's perception of predation risk may depend on manyfactors, such as distance to refuge and group size, but it isunclear whether individuals respond to different factors ina similar manner. We tested whether flocks of foraging starlingsresponded in the same way to an increased perception of predationrisk by assessing three factors: (1) neighbor distances, (2)habitat obstruction, and (3) recent exposure to a predator.We found that in all three scenarios of increased risk, starlingsreduced their interscan intervals (food-searching bouts), whichincreased the frequency of their vigilance periods. We thenexamined how one of these factors, habitat obstruction, affectedescape speed by simulating an attack with a model predator.Starlings were slower to respond in visually obstructed habitats(long grass swards) and slower when they had their head downin obstructed habitats than when they had their head down inopen habitats. In addition, reaction times were quicker whenstarlings could employ their peripheral fields of vision. Ourresults demonstrate that different sources of increased riskcan generate similar behavioral responses within a species.The degree of visibility in the physical and social environmentaffects both the actual and perceived risk of predation.     

Egg-brooding, body size and predation risk in planktonic marine copepods

We investigated the interacting effects of copepod body size and the presence or absence of egg masses on the risk of predation by a visual predator. We conducted selection experiments involving three-spined sticklebacks (Gasterosteus aculeatus) and copepods ranging in body mass from 0.5 to 740 μg C: Oithona similis, Corycaeus anglicus, Pseudocalanus newmani, P. moultoni, Pseudodiaptomus marinus, and Paraeuchaeta elongata. We found that sticklebacks selected ovigerous females of the two smallest-bodied species of copepods (Oithona similis and Corycaeus anglicus). In contrast, the fish showed no significant selection for ovigerous females of the remaining, larger-bodied species. Unexpectedly, egg mass position (i.e., in a ventral, dorsal or lateral location on the urosome) appeared to influence predation risk more than did body size, resulting in higher predation risk for the cyclopoid and poecilostomatoid species than for the calanoid species we tested. Although the sticklebacks showed no statistically significant preference for ovigerous females of any of the four calanoid species, for each species the overall proportion of ovigerous females ingested was slightly greater than 0.50. Thus, whether body size influences the susceptibility of egg-brooding calanoid copepods to predation remains an open question. Received: 24 August 1998 / Accepted: 6 July 1999     

The effects of group size and reproductive status on vigilance in captive Callithrix jacchus

Previous work on mammals and birds has often demonstrated a negative relationship between group size and individual vigilance. However, this relationship has received only weak support in nonhuman primates. This result may be due to the failure to distinguish different forms of vigilance such as antipredatory vigilance and social monitoring. Here, we tested the effects of group size, reproductive status (breeding vs. nonbreeding), and sex on antipredatory vigilance and social monitoring in captive common marmosets (Callithrix jacchus). Behavioral observations using one-zero sampling were conducted on adult members of three captive groups of small, medium, and large size. Data were analyzed using a series of general linear models (GLMs) analyses of covariance (ANCOVAs). We found an overall negative group size effect on antipredatory vigilance and that breeders, especially breeding males, were significantly more vigilant than nonbreeders. Conversely, we found that social monitoring increased with group size. Unlike the results for antipredatory vigilance, neither breeders and nonbreeders nor males and females differed in their amounts of social monitoring. However, the effect of group size appeared to differ for nonbreeding males compared to all other adults. Our results generally support the idea that individuals in larger groups are safer with breeding males likely playing a prominent role in protection from predation. The increase in social monitoring may be related to increased reproductive competition with the presence of adult offspring, but future studies need to clarify the target of social monitoring in both breeders and nonbreeders. Overall, the study underlines the importance of distinguishing different forms of vigilance and other factors as they may confound the effects of group size on antipredatory vigilance.     

Disturbance and predation risk influence vigilance synchrony of black‐necked cranes Grus nigricollis,but not as strongly as expected

Animals monitor surrounding dangers independently or cooperatively (synchronized and coordinated vigilance), with independent and synchronized scanning being prevalent. Coordinated vigilance, including unique sentinel behavior, is rare in nature, since it is time‐consuming and limited in terms of benefits. No evidence showed animals adopt alternative vigilance strategies during antipredation scanning yet. Considering the nonindependent nature of both synchronization and coordination, we assessed whether group members could keep alert synchronously or in a coordinated fashion under different circumstance. We studied how human behavior and species‐specific variables impacted individual and collective vigilance of globally threatened black‐necked cranes (Grus nigricollis) and explored behavior‐based wildlife management. We tested both predation risk (number of juveniles in group) and human disturbance (level and distance) effects on individual and collective antipredation vigilance of black‐necked crane families. Adults spent significantly more time (proportion and duration) on scanning than juveniles, and parents with juveniles behaved more vigilant. Both adults and juveniles increased time allocation and duration on vigilance with observer proximity. Deviation between observed and expected collective vigilance varied with disturbance and predation risk from zero, but not significantly so, indicating that an independent vigilance strategy was adopted by black‐necked crane couples. The birds showed synchronized vigilance in low disturbance areas, with fewer juveniles and far from observers; otherwise, they scanned in coordinated fashion. The collective vigilance, from synchronized to coordinated pattern, varied as a function of observer distance that helped us determine a safe distance of 403.75 m for the most vulnerable family groups with two juveniles. We argue that vigilance could constitute a prime indicator in behavior‐based species conservation, and we suggesting a safe distance of at least 400 m should be considered in future tourist management.     

Patch use, apprehension, and vigilance behavior of Nubian Ibex under perceived risk of predation

Foraging theory predicts that animals will sacrifice feedingeffort in order to reduce predation risk. Once a forager choosesa habitat, it must decide how to allocate its foraging effort.Nubian Ibex are diurnal, social, cliff-dwelling herbivores.Many of their characteristics seem to have evolved as responsesto predation risk. In order to assess the effects that perceivedrisk of predation might have on foraging behavior of free-rangingNubian Ibex in the Negev Desert, Israel, we measured giving-updensities (GUDs) in artificial food patches and used them togauge apprehension level. (Apprehension can be defined as areduction in attention devoted to performing an activity asa consequence of reallocating attention to detecting or respondingto predation risk. A forager can also be vigilant. Vigilanceis often defined as time spent scanning the surroundings withthe head up.) We also quantified time budgeting using focalobservation of individual Nubian Ibex. Habitat preferences andpatch selectivity as a measure of apprehension were considered.In particular, we tested the effect of distance from refugeon GUDs, the effect of micropatch structure on selectivity,and the effect of distance from the refuge and group size onNubian Ibex vigilance level and apprehension. Nubian Ibex allocatetheir foraging effort more toward patches closer to the escapeterrain. At the same time, Nubian Ibex are more apprehensiveat intermediate distances from the cliff edge than nearer thecliff, and their use of vigilance increases with distance fromthe cliff edge. These results suggest that Nubian Ibex may switchfrom apprehension to a more extreme behavior of vigilance atgreater distances from the refuge. This study demonstrated theuse of antipredatory behaviors, apprehension, and vigilanceby a forager. Estimating apprehension and vigilance levels ofa forager simultaneously gives a more complete and accuratepicture of how the habitat is perceived by them and combinedwith measurements of GUD allow a more accurate assessment ofhabitat quality.     

季节、性别和群体大小对鹅喉羚警戒行为的影响

动物通过集群降低个体警戒时间,从而增加采食等行为时间,这种现象被称为" 群体效应" 。除群体大小
外,社会及环境因子如季节与性别也可能影响个体警戒水平。本文于2007 年至2009 年在新疆卡拉麦里山有蹄类
野生动物保护区采用焦点动物取样法,通过测定鹅喉羚警戒行为比例、平均每次警戒持续时间及10 min内警戒频
率,研究了季节、性别及群体大小对鹅喉羚个体警戒水平的影响,并验证群体效应。结果表明:由于季节更替
而产生的生物量的变化对鹅喉羚个体警戒水平无显著影响;在秋冬季除雄性外,鹅喉羚个体警戒水平均有随群
体增大而降低的趋势,但这种趋势并不十分明显。性别则显著影响其警戒水平,夏季由于雌性羚羊处于哺乳期,
因而其警戒水平显著高于雄性(P < 0.05);受繁殖行为影响,冬季雄性比雌性警觉性更高(P > 0. 05);春秋季
两性间警戒水平没有差异(P >0.05)。不同生理周期是导致鹅喉羚育幼期雌性及繁殖期雄性个体警戒水平发生
显著变化的重要因子。