Anthrax outbreak among Grevy's zebra (Equus grevyi) in Samburu, Kenya

An anthrax outbreak occurred in the Wamba area of southern Samburu, Kenya, between December 2005 and March 2006. The outbreak affected equids including the endangered Grevy's zebras (Equus grevyi), plain zebras (Equis Burchelli) and donkeys (Equus asinus). Most of the deaths were localized in Nkaroni area just west of Wamba town. The diagnosis of anthrax was rapidly confirmed by bacteriological methods. The relevant government departments, including the Kenya Wildlife Service and Veterinary Department, and other stakeholders were promptly informed. Fifty‐three Grevy's zebra and 26 plains zebras died from anthrax. An equal number (eighteen) of adult male and female Grevy's zebras succumbed to the disease. The outbreak affected immature and mature individuals equally. The dead plain zebras included fifteen adult females, two adult males and nine immature individuals. The Veterinary Department responded by vaccinating livestock while Kenya Wildlife Service vaccinated 620 Grevy's zebras within southern Samburu. Examination of sites at which carcasses of animals which succumbed to the disease were burnt, revealed that unsupervised burning did not eliminate anthrax spores in 42% of the cases (n = 14). There is an urgent need to incorporate strategic wildlife disease monitoring in the struggle to save Grevy's zebras and other endangered species.     

Divergent water requirements partition exposure risk to parasites in wild equids

For grazing herbivores, dung density in feeding areas is an important determinant of exposure risk to fecal‐orally transmitted parasites. When host species share the same parasite species, a nonrandom distribution of their cumulative dung density and/or nonrandom ranging and feeding behavior may skew exposure risk and the relative selection pressure parasites impose on each host. The arid‐adapted Grevy''s zebra (Equus grevyi) can range more widely than the water‐dependent plains zebra (Equus quagga), with which it shares the same species of gastrointestinal nematodes. We studied how the spatial distribution of zebra dung relates to ranging and feeding behavior to assess parasite exposure risk in Grevy''s and plains zebras at a site inhabited by both zebra species. We found that zebra dung density declined with distance from water, Grevy''s zebra home ranges (excluding those of territorial males) were farther from water than those of plains zebras, and plains zebra grazing areas had higher dung density than random points while Grevy''s zebra grazing areas did not, suggesting a greater exposure risk in plains zebras associated with their water dependence. Fecal egg counts increased with home range proximity to water for both species, but the response was stronger in plains zebras, indicating that this host species may be particularly vulnerable to the elevated exposure risk close to water. We further ran experiments on microclimatic effects on dung infectivity and showed that fewer nematode eggs embryonated in dung in the sun than in the shade. However, only 5% of the zebra dung on the landscape was in shade, indicating that the microclimatic effects of shade on the density of infective larvae is not a major influence on exposure risk dynamics. Ranging constraints based on water requirements appear to be key mediators of nematode parasite exposure in free‐ranging equids.     

Effects of lions on behaviour and endocrine stress in plains zebras

Living under predation risk may alter both behaviour and physiology of potential prey. In extreme cases, such alterations may have serious demographic consequences, and recent studies support that non‐lethal effects of predation may have broad ecological consequences. However, behavioural and physiological responses to predation risk may be related to trade‐offs associated with resource acquisition and direct predation risk. We validated an enzyme‐linked immunoassay (EIA) for non‐invasive monitoring of stress in plains zebras (Equus quagga) from faecal material. We used this assay in combination with behavioural data to assess if plains zebras living with and without lions (Panthera leo) in a mountain savannah in southern Africa differed in behaviour and physiology, and if such differences were influenced by seasons with contrasting resource availability. Zebra group sizes did not differ between areas with and without lions, but zebra groups had more juveniles in an area with lions than groups in an area without lions, but only during the wet season. Similarly, we observed differences in individual vigilance, foraging behaviour and stress hormone concentrations, but all these differences were influenced by seasons. Despite these seasonal influences, our study did not suggest that zebras in an area with lions spent a higher proportion of time being vigilant, a lower proportion of time foraging, or had higher stress hormone levels. Our results instead suggest that zebras' responses to lion presence were highly context dependent and the result of complex interactions between resource abundance and cues about predation risk. Because of the obvious ecological and evolutionary ramifications of such findings, we argue that further research is needed to define the spatial and temporal scales over which predators impose indirect effects on their prey.     

Collective Vigilance in the Wintering Hooded Crane: The Role of Flock Size and Anthropogenic Disturbances in a Human‐Dominated Landscape

Vigilance achieved at the group level, known as collective vigilance, can enhance the ability to assess threats and confer benefits to gregarious prey species. Examining the factors that influence collective vigilance and exploring how individual vigilance is organized at the group level can help to understand how prey groups respond to potential threats. We quantified collective vigilance and determined its temporal pattern in a natural wintering population of the hooded crane Grus monacha in the Shengjin Lake reserve in China. We examined the role of flock size and anthropogenic disturbances in the human‐dominated landscape on collective vigilance and level of synchronization. The proportion of time during which at least one individual scanned the surroundings (collective vigilance) increased with flock size and was higher in the more disturbed buffer zone of the lake. Synchronization of vigilance occurred more frequently in the smaller flocks but was not related to the risk of disturbance. Synchronization implies that individuals tend to monitor and copy the vigilance of neighbors. In the degraded wetlands, the wintering hooded crane benefits from foraging in groups and synchronizing their vigilance in response to human disturbances.     

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

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.     

印度喜马拉雅山区西藏盘羊的警戒行为

在几个动物类群中开展的许多行为研究中发现,个体的警觉水平与群体大小存在着负相关关系。一般认为,这种关系是由于个体在一个较大的群体中被捕杀的概率小。在本研究中,我研究了濒危的印度喜马拉雅地区西藏盘羊(Ovis ammon hodgsoni)的警戒行为与群体大小和逃逸地形的关系。我假设小群体中的、位于悬崖旁的盘羊比那些大群体中的、开阔地带(逃逸地形)中的盘羊的警戒水平高。结果发现随着群体增大,盘羊的警戒水平下降,但是,逃逸地形与盘羊的警戒水平没有关系。盘羊的不同性别、年龄组之间的时间预算存在显著差异。与雄性和亚成年个体比较,雌性用于警觉的时间多,它们比雄性采食时间长,移动少。因此,警戒行为是是盘羊的一种重要反捕食行为     

Human Disturbances,Habitat Characteristics and Social Environment Generate Sex-Specific Responses in Vigilance of Mediterranean Mouflon

In prey species, vigilance is an important part of the decision making process related to predation risk effects. Therefore, understanding the mechanisms shaping vigilance behavior provides relevant insights on factors influencing individual fitness. We investigated the role of extrinsic and intrinsic factors on vigilance behavior in Mediterranean mouflon (Ovis gmelini musimon×Ovis sp.) in a study site spatially and temporally contrasted in human pressures. Both sexes were less vigilant in the wildlife reserve compared to surrounding unprotected areas, except for males during the hunting period. During this period, males tended to be less strictly restricted to the reserve than females what might lead to a pervasive effect of hunting within the protected area, resulting in an increase in male vigilance. It might also be a rutting effect that did not occur in unprotected areas because males vigilance was already maximal in response to human disturbances. In both sexes, yearlings were less vigilant than adults, probably because they traded off vigilance for learning and energy acquisition and/or because they relied on adult experience present in the group. Similarly, non-reproductive females benefited of the vigilance effort provided by reproductive females when belonging to the same group. However, in the absence of reproductive females, non-reproductive females were as vigilant as reproductive females. Increasing group size was only found to reduce vigilance in females (up to 17.5%), not in males. We also showed sex-specific responses to habitat characteristics. Females increased their vigilance when habitat visibility decreased (up to 13.8%) whereas males increased their vigilance when feeding on low quality sites, i.e., when concomitant increase in chewing time can be devoted to vigilance with limited costs. Our global approach was able to disentangle the sex-specific sources of variation in mouflon vigilance and stressed the importance of reserves in managing and conserving wild sheep populations.     

Stability and Dynamics of Group Composition in a Herd of Captive Plains Zebras

Although the social structure in a safari park population of plains zebras is similar to that observed in the wild, a number of behavioural differences between the two situations were found. Unlike in the wild situation, stallions expelled their own offspring, generally directly after the birth of a sibling. Other individuals frequently joined the stallion in expulsion behaviour. Harems remained intact in spite of the absence of the stallion. Stallions did not abduct young females, as in the wild, but they did abduct adult females when these were in estrus. Stallions further expelled adult mares which hindered them. The prominent role of the stallion in regulating group size could mean that the competition experienced in the safari park is harder for stallions than it is for mares. Young females not expelled from their natal harem go through a “wandering phase”, visiting other groups. After that they exert female choice when they eventually join a group or an individual.     

Habitat use and movements of plains zebra (Equus burchelli) in response to predation danger from lions

Prey species must adapt their behavior to avoid predation. Asa key prey item for lions (Panthera leo), plains zebras (Equusburchelli) were expected to respond to immediate threats posedby lions in their area. In addition, zebras were predicted toexhibit behavior tuned to reduce the potential for encounterswith lions, by modifying their movement patterns in the timesof day and habitats of greatest lion danger. We studied a populationof approximately 600 plains zebra living in Ol Pejeta Conservancy,Kenya. We found that zebra abundance on or near a grasslandpatch was lower if lions had also been observed on that patchduring the same day. Predation danger was highest in grasslandhabitat during the night, when lions were more active. Zebrasightings and global positioning system radio collar data indicatedthat zebras also reduced their use of grassland at night, insteadusing more woodland habitat. Zebras moved faster and took sharperturns in grassland at night. It is hypothesized that these moreerratic movements assist zebras in avoiding detection or captureby lions.     

Clinical and Pathologic Features of a Suspected Selenium Deficiency in Captive Plains Zebras

Previous studies have shown that selenium (Se) deficiency is associated with nutritional myopathy, known as white muscle disease (WMD), in horses. However, correlations between Se deficiency and clinical findings, such as hematologic biochemical values and pathological features, have not been evaluated in captive plains zebras. The purpose of the present study was to investigate the clinical and pathologic features that may be caused by a Se deficiency in the captive plains zebra. Clinical findings, feed analyses, hematologic biochemical analyses, response to treatment, and pathologic examination were assessed in six affected plains zebras. The dietary concentration of Se in feed was also tested. Sudden death occurred in two cases during the first day of the onset of symptoms. Two zebras died at 4 days and two zebras survived after treatment. The clinical signs in affected animals were characterized by general weakness, astasia, and abnormal postural positions. The Se concentration in hay from the breeding stable was low, based on the reference value. Glutathione peroxidase (GSH-Px) activity was lower compared with the equine reference value. Multiple areas of subcutaneous steatitis and pale skeletal muscle and myocardium were revealed at gross necropsy. Degeneration and necrosis of myocardial and skeletal muscles, as well as congestion of the liver, lung, and kidney were found via histopathological examination. No suspected bacterial infections were found. Feed analyses, response to treatment, serum GSH-Px activity, and pathological features suggest that Se deficiency may have caused the disease in the six affected captive plains zebra.     

Long‐Term Population Survey of the Sulawesi Black Macaques (Macaca nigra) at Tangkoko Nature Reserve,North Sulawesi,Indonesia

The Sulawesi black macaque (Macaca nigra) population at Tangkoko Nature Reserve in North Sulawesi, Indonesia has been the focus of periodic study for over 30 years. The population has shown considerable decline during much of that time. Here we present the results of a long‐term population survey of the Tangkoko M. nigra, conducted over the past decade, to provide updated information and on‐going assessment of the population. Line‐transect sampling was conducted annually from 1999 to 2002 and 2005 to 2011 along the same transect during a 2‐ to 3‐week survey period. Although further decline in the population was observed at the outset of the survey, over the subsequent 12‐year period we have seen stability in the population parameters with evidence of modest increases in both group and population density. During the 1999–2002 survey periods, there was a mean group density of 3.6 groups/km² and a mean population density of 39.8 individuals/km². During 2005–2011, mean group density increased to 3.8 groups/km² and mean population density was 51.4 individuals/km². The 2011 survey data indicated an estimated group density of 4.3 groups/km² and a population density of 61.5 individuals/km². Given that our transect was located in the core of the Tangkoko reserve, our density estimates should be limited to that area of the reserve. One explanation for the apparent stabilization of the population may be tied to the increasing and sustained number of training and research programs being conducted at the reserve. This collective effort by local and international groups may be helping to reduce illegal activity in the reserve (i.e., hunting and habitat destruction) and generate greater awareness of this critically endangered species. Without the continued vigilance afforded by the existing research and training programs and the support and involvement of the local people, the M. nigra at the Tangkoko Nature Reserve will likely face further decline. Am. J. Primatol. 75:88‐94, 2013. © 2012 Wiley Periodicals, Inc.     

Ethological investigations on a herd of plains zebra in a safari park: Time-budgets,reproduction and food competition

The social organization of a herd of 25 plains zebras under safari park conditions and the time-budgets of 18 individuals from this herd were investigated. The zebras had organized themselves in harem groups. Stallions appeared to spend more time acting socially than did other sex-age classes and they spent less time feeding. Social behaviours were mainly directed against other stallions. Stallions were also more on the alert. The time-budget of safari park zebras largely agrees with that of their wild counterparts. From data on time budgets and from differences in the reproductive output of adults of different ranks it is concluded that differential access to food plays an important role in the safari park.     

半散放条件下普通斑马的种群特征

<正>普通斑马又称平原斑马(Equus burchelli),隶属于奇蹄目马科,是一种极具观赏价值的大型哺乳动物。广泛分布于非洲,喜欢栖息在平原和草原,随季节和食物迁徙。普通斑马是社会性动物,习惯群体生活,规模较小的群体由1只雄性和2-6只雌性以及它们未成年的子女组成;或是由十几只未成年的雄性普通斑马组成;较大的群体则有几百只,它们通常是由若干个小规模的群体组成。雄性     

On the Advantages of Mixed‐Species Groups: Impalas Adjust Their Vigilance When Associated With Larger Prey Herbivores

Prey can obtain valuable benefits from associating with other species if heterospecifics help to detect predators or locate good food patches. In mixed‐species groups, how species respond to the presence of other species remains a poorly explored question although it might give crucial insights into mechanisms underlying the interspecific coexistence. We studied temporary mixed‐species groups of large herbivores in Hwange National Park (Zimbabwe) between the common impala (Aepyceros melampus), the focal species here, and bigger species including the plains zebra (Equus quagga), the greater kudu (Tragelaphus strepsiceros) or the blue wildebeest (Connochaetes taurinus). In the Hwange savanna, the focal and smaller species are exposed to a larger range of predators than the associated species. In this context, we investigated how impalas adjusted their vigilance with group size comparing impala‐only and mixed‐species groups and whether the identity of heterospecifics affected vigilance of impalas. Our study showed that the time impalas spent in vigilance significantly decreased with group size when they formed impala‐only groups, whereas it did not significantly vary with group size in mixed‐species groups. Moreover, in mixed‐species groups, impalas did not adjust their time spent in vigilance with the proportion of conspecifics and the identity of the associated species. Thus, the mechanism underlying the difference of impalas' behavioural adjustment of vigilance with group size between single‐ and mixed‐species groups seemed to be related to the presence but not to the number and the identity of heteropecifics. Finally, we discuss the concept that larger and dominant heterospecifics were likely to increase competition for food access, thereby forcing higher vigilance of impalas, outweighing any reduction from collective vigilance.     

Vigilance in a Cooperatively Breeding Primate

Collective vigilance is considered a major advantage of group living in animals. We investigated vigilance behavior in wild mustached tamarins (Saguinus mystax), small, arboreal, cooperatively breeding New World primates that form stable mixed-species groups with saddleback tamarins (Saguinus fuscicollis). We aimed 1) to investigate whether vigilance patterns change according to individual activity and 2) to examine whether there is a social component of vigilance in their cooperative and nonaggressive society. We studied 11 factors that may influence vigilance and used this data to interpret the possible functions of vigilance. We observed 44 individuals in 3 mixed-species and 2 single-species groups of 2 populations that differed in population density and home range sizes. Vigilance changed greatly when individuals were engaged in different activities and individual vigilance was affected by different sets of factors depending on the activity. As vigilance decreased in proximity of conspecifics and heterospecifics when feeding, and in larger mixed-species groups when resting, we conclude that the predominant function of vigilance in mustached tamarins is predator related. However, the absence of the group size effect in very large single-species groups suggests that it may also function to maintain group cohesion. In the population with higher density and smaller home ranges individuals also increased their vigilance in home range overlap areas. We found no evidence that mustached tamarins monitor group mates to avoid food stealing or aggression. The effect of heterospecifics on individual vigilance suggests that collective vigilance might have been an important incentive in the evolution of tamarin mixed-species groups.     

Vocal identification of individual African Wood Owls Strix woodfordii: a technique to monitor long-term adult turnover and residency

The hoot-calls of Wood Owls Strix woodfordii , recorded in the Kruger National Park, South Africa, from 1986 to 1998, are sufficiently different to distinguish individuals. Thirteen hoot-call variables, measured from recordings over this period, show that male and female Wood Owls have such temporal stability that these calls can be used reliably as a long-term census technique. manova , based on ordinations from principal component analysis, was used to identify individuals statistically between sampling periods. A forward stepwise discriminant function analysis achieved 100% classification success of individual male ( n  = 3) and female ( n  = 4) owls from a single sampling period. For all the individuals recorded over the whole study period we achieved a classification success of 80.9% ( n  = 9) for male hoot calls and of 96.3% ( n  = 13) for female calls. We found mean occupation periods of 82.25 and 65 months and annual turnover rates of 19.3% and 13.65% for males and females, respectively. Our survey, using vocalizations, is unique since we use data collected over a 12-year period to derive estimates of population turnover in Wood Owls, and consider what questions can be addressed in similar studies.     

Population Survey and Demographic Features of a Coastal Island Population of <Emphasis Type="Italic">Alouatta clamitans</Emphasis> in Atlantic Forest,Southeastern Brazil

Brown howlers (Alouatta clamitans) are endemic to the Atlantic Forest. Because only 7.5% of this fragmented forest remains in Brazil, there is an urgent need for studies of its ecology. Understanding island populations, still poorly researched in the relatively well-studied Alouatta, can provide important information for understanding habitat fragmentation and conservation. We studied brown howlers on the northern portion of the coastal and protected island, Ilha do Cardoso State Park. We used distance sampling methods on 5 transects to estimate population density of the howlers. Estimated howler density on the island is 10.6 individuals/km², with a total of 36 (21–62) individuals in a 3.4 km² area. The density is low, but similar to that of other large and preserved areas. By triangulating on vocalization and following groups, we estimate that there are 10 groups with an average of 4.5 individuals per group. Groups comprise 42% adult females, 27% adult males, 20% juveniles, 7% infants, and the remaining 4% subadult males. Howlers apparently use all appropriate habitats, including Atlantic Forest of plains and slopes. We believe that the howler population is maintaining a typical replacement on the island, with low birth rates and high survival rates, but long-term studies are required to test this. Small group size and associated social structure may be due to the particular environmental conditions on Ilha do Cardoso State Park.     

Investigating Differences in Vigilance Tactic Use within and between the Sexes in Eastern Grey Kangaroos

Aggregation is thought to enhance an animal’s security through effective predator detection and the dilution of risk. A decline in individual vigilance as group size increases is commonly reported in the literature and called the group size effect. However, to date, most of the research has only been directed toward examining whether this effect occurs at the population level. Few studies have explored the specific contributions of predator detection and risk dilution and the basis of individual differences in the use of vigilance tactics. We tested whether male and female (non-reproductive or with young) eastern grey kangaroos (Macropus giganteus) adopted different vigilance tactics when in mixed-sex groups and varied in their reliance on predator detection and/or risk dilution as group size changed. This species exhibits pronounced sexual dimorphism with females being much smaller than males, making them differentially vulnerable toward predators. We combined field observations with vigilance models describing the effects of detection and dilution on scanning rates as group size increased. We found that females with and without juveniles relied on predator detection and risk dilution, but the latter adjusted their vigilance to the proportion of females with juveniles within their group. Two models appeared to equally support the data for males suggesting that males, similarly to females, relied on predator detection and risk dilution but may also have adjusted their vigilance according to the proportion of mothers within their group. Differential vulnerability may cause sex differences in vigilance tactic use in this species. The presence of males within a group that do not, or only partially, contribute to predator detection and are less at risk may cause additional security costs to females. Our results call for reexamination of the classical view of the safety advantages of grouping to provide a more detailed functional interpretation of gregariousness.     

Number of neighbors instead of group size significantly affects individual vigilance levels in large animal aggregations

The group size effect states that animals living in groups gain anti‐predator benefits through reducing vigilance levels as group size increases. A basic assumption of group size effect is that all individuals are equally important for a focal individual, who may adjust its vigilance levels according to social information acquired from them. However, some studies have indicated that neighbors pose greater influences on an individual's vigilance decisions than other group members, especially in large aggregations. Vigilance has also been found to be directed to both predators (anti‐predation vigilance) and conspecifics (social vigilance). Central individuals might rely more on social vigilance than peripheral individuals. To test these hypotheses, we examined the effects of flock size, number of neighbors and position within a flock on vigilance and competition of greater white‐fronted goose Anser albifrons that form large foraging flocks in winter, controlling the effects of other variables (group identity, winter period and site). We found that individual vigilance levels were significantly affected by number of neighbors and position within a flock, whereas flock size showed no effect. Individuals devoted a large component of vigilance to nearby flock mates. Central individuals directed a relatively larger proportion of vigilance to monitor neighbors than peripheral ones, indicating that central individuals more relied on social information acquired from neighbors, possibly caused by the more blocked visual field of central individuals. Moreover, some social vigilance may function as conducting or preventing agonistic interactions since competition intensity was positively correlated with number of neighbors. Our study therefore demonstrate that the number of neighbors is more important than group size in determining individual vigilance in large animal groups. Further studies are still needed to unravel which neighbors pose greater influence on individual vigilance, and the factors that influence individuals to acquire information from their neighbors to adjust vigilance behaviors.