高原鼠兔与达乌尔鼠兔的摄食行为及对栖息地适应性的研究

通过对标志高原鼠兔和达乌尔鼠兔直接观察的方法,对它们的摄食行为及栖息地适应性进行了研究。两种鼠兔的摄食行为链存在着明显趋同的行为程序时间系列。在摄食活动中,前者用于防御敌害的时间分配较多。而达乌尔鼠兔则花费更多的时间于采食。对小生境内的高大植株进行刈割,是高原鼠兔保持其防御视野开阔,降低被捕食风险的适应性策略;达乌尔鼠兔则善于利用栖息地内高大植株覆盖物作为它们的临时隐蔽所,以有效地躲避敌害。这表明它们具有反捕食的行为调控能力,也证明捕食风险强化了物种对栖息地的选择。     

相关风险因子对高原鼠兔摄食行为的影响

研究了捕食风险环境中集和洞口距离对高原鼠兔摄食行为的影响。结果表明,集群数量的增加不仅降低了警觉行为,同时也减少了摄食行为,在高风险环境中,集群为1时的取食行为强度最大,低风险环境中,为0时最大,警觉行为主要出现在距洞口2m的范围内,其行为强度与洞口踪影职责负相关,当洞口距离大于3m时,风险处理区的高原鼠兔几乎无警觉行为出现,且该处理区的取食区域几乎压缩的洞口旁,研究结果表明,在捕食风险环境中,高原鼠兔摄食行为与集群和洞口距离之间具有复杂的关系,其行为决策反映了降低风险与摄取食物间的权衡,行为目标是在降低捕食风险的同时尽可能地取食食物。     

捕食风险对高原鼠兔行为的影响

我们在野外条件下利用赤狐的粪尿增加高原鼠兔的捕食风险 ,采用目标动物抽样法对高原鼠兔的 5种行为进行观察 ,分析天敌动物气味增加与天敌动物数量增加对高原鼠兔行为影响的差异 ,探讨高原鼠兔对捕食风险的权衡能力及面对不同风险的行为决策。 2 0 0 1年 ,在捕食风险处理样方中观察雄性成体 1 8只 ,雌性成体2 5只 ,雄性幼体 35只和雌性幼体 4 2只 ,在对照样方中观察雄性成体 1 4只 ,雌性成体 1 5只 ,雄性幼体 2 2只和雌性幼体 1 1只 ;2 0 0 2年 ,在捕食风险处理样方中观察雄性成体 7只 ,雌性成体 1 2只 ,在对照样方中观察雄性成体 8只 ,雌性成体 1 5只。研究结果表明 :增加赤狐的气味后 ,高原鼠兔通过改变行为策略以适应捕食风险的增加。当气味源刚放入后 ,与对照样方比较 ,高原鼠兔明显增加了观察和鸣叫的频次 ,相应减少了取食的频次 ,且随着时间的推移 ,高原鼠兔并未对气味产生适应性。当天敌动物的数量增加后 ,赤狐气味的增加对高原鼠兔行为的影响较小 ,在捕食风险超出高原鼠兔的耐受范围时 ,高原鼠兔扩散。同时 ,高原鼠兔的行为在雌雄之间、成体与幼体之间没有明显的不同 ,雌雄个体、成幼体均采用相同的行为策略减小捕食风险。以上结果表明 :捕食风险明显影响高原鼠兔的行为 ,高原鼠兔能够权衡捕食     

赤狐气味对高原鼠兔繁殖的影响

在野外条件下,利用赤狐的粪尿气味增加高原鼠兔的捕食风险,研究捕食风险对高原鼠兔繁殖的影响。结果表明,作为衡量高原鼠兔繁殖投入大小的定量指标,成体高原鼠兔的体重变化在捕食风险处理样方与对照样方之间没有明显的不同,随着繁殖期的延长,两样方内雌雄个体的体重均显减少,说明捕食风险对高原鼠兔的繁殖投入无明显影响,因此,捕食风险对幼体的生长、发育也无明显的作用。捕食风险增加后,高原鼠兔平均每个雌性成体拥有的后代数目、性比和居留率与对照样方比较均无明显不同,但是由于扩散等原因使每个雄性成体拥有的后代数、繁殖期结束后幼体的性比有明显的差异。以上结果并未显示出捕食气味作为捕食风险对高原鼠兔的繁殖产生抑制作用,其主要原因是捕食风险的类型不同和研究期间高原鼠兔本身承受的捕食风险较大,高原鼠兔可能通过行为变化调节捕食风险增加对其产生的不利影响。     

高寒草甸生态系统中高原鼠兔和高原鼢鼠的捕食风险及生存对策

调查青藏高原高寒草甸生态系统中两种主要啮齿动物及其天敌动物的种群密度,分析天敌动物对两种啮齿类的捕食方式、捕食强度,探讨啮齿类动物的捕食风险及生存对策。研究结果表明,高原鼠兔和高原鼢鼠的种群密度分别为4．97只／hm^2和10．6只／hm^2,而它们的主要天敌赤狐、艾虎和香鼬的种群密度分别为0．16只／100hm^2、0．37只／100hm^2、3只／100hm^2。艾虎和香鼬在取食过程中主要搜寻啮齿类的洞道系统,全部食物几乎都来源于洞道系统内;赤狐或取食地面活动的鼠兔,或挖掘洞口待高原鼢鼠封闭洞口时取食猎物。高原鼠兔在赤狐、艾虎和香鼬的食物中所出现的频次分别为100％、96．1％、100％,高原鼢鼠在3种天敌动物的食物中所出现的频次分别为87．5％、73．2％、0％。3种天敌动物对高原鼠兔和高原鼢鼠的捕食强度分别为0．703％和0．038％,高原鼠兔和高原鼢鼠所承受的捕食风险分别为0．780和0．393。高原鼠兔在高的捕食风险下通过行为对策和繁殖对策增加其适合度,而承受捕食风险较小的高原鼢鼠主要通过封闭的洞道系统和高的存活率增加其适合度。     

捕食风险对高原鼠兔食物大小选择的影响

文章报道了捕食风险条件下高原鼠兔对食物大小选择的格局。在实验箱中放置艾虎以改变捕食风险水平, 食物按体积大小分为4种食物项目, 并测定各项目摄入率和取食单个食物项目的进食时间, 结果表明, 摄入率与进食时间依食物项目体积的增大而增加。将大食物与小食物项目配对并供高原鼠兔选择时, 食物项目的利用率视环境状况而不同。捕食风险处理中, 小食物利用率依其进食时间的减少而增加, 其程度与所配对的食物项目的摄入率和进食时间有关。在捕食风险的作用下, 高原鼠兔的食物选择格局反映了能量摄取与风险避免间的权衡。     

不同海拔地区高原鼠兔探究性和静止代谢率的差异

环境的差异影响动物种群生活史对策的进化。对地理分布范围广的物种而言,栖息地环境差异大,不同种群的生活史对策亦存在显著差异。个性特征作为生活史的一部分,反映了动物对环境的适应模式。前期研究表明,不同海拔区域的高原鼠兔的生活史对策存在显著差异,然而,其个性特征及与能量代谢的关联性是否也存在差异,目前尚不清楚。2018年9-10月,分别在海拔3268 m的贵南县和3980 m的玛沁县测定当地高原鼠兔的探究性与静止代谢率。结果发现,高海拔雄性高原鼠兔的探究性显著低于低海拔雄性个体;高海拔雌性高原鼠兔体重矫正静止代谢率显著高于低海拔雌性个体。高海拔地区,雌性高原鼠兔的探究性和体重矫正静止代谢率呈显著正相关,雄性高原鼠兔的探究性和体重呈显著负相关;低海拔地区,高原鼠兔的探究性和体重矫正静止代谢率或体重之间均无显著相关性。该结果 表明,调整个性特征和能量代谢及其两者的关联性也是高原鼠兔适应不同海拔栖息地环境差异的生活史对策之一。     

植物生长季节不同栖息地高原鼠兔的食物选择

本文采用胃内容物镜检分析法,对栖息于青藏高原矮嵩草草甸、垂穗披碱草草甸和杂类草草甸中的高原鼠兔的主要食物组成进行了比较分析,旨在探讨栖息地变化对高原鼠兔食物组成的影响,揭示高原鼠兔对栖息地变化的生存对策和适应性.研究结果表明:在矮嵩草草甸,高原鼠兔主要取食垂穗披碱草、早熟禾、蓝花棘豆和甘肃棘豆;在垂穗披碱草草甸,主要选择垂穗披碱草、甘肃棘豆、蓝花棘豆、矮嵩草和二柱头蔗草;在杂类草草甸,喜食植物种类为垂穗披碱草、蓝花棘豆、甘肃棘豆、早熟禾、弱小火绒草、长茎藁本、兰石草和红花岩生忍冬.在整个植物生长季节,高原鼠兔在3种栖息地共取食27种植物,其中垂穗披碱草、甘肃棘豆和蓝花棘豆在不同栖息地中选择指数较高,为高原鼠兔优先选择的食物;在不同栖息地,高原鼠兔取食植物有差别,垂穗披碱草草甸为16种、矮嵩草草甸为22种,杂类草草甸为24种;喜食食物比例也存在着明显差别,在垂穗披碱草草甸,垂穗披碱草比例高达40.5%,在矮嵩草草甸,甘肃棘豆比例也达到23.7%,而在杂类草草甸,选食比例最高的兰石草仅为14.6%,说明在该草甸高原鼠兔食物选择呈现泛化趋势.相似性指数分析结果也表明,杂类草草甸中高原鼠兔主要食物组成与其它两种栖息地有较大的区别.从而说明当栖息地植物群落种类组成发生变化后,高原鼠兔可以通过改变其食物组成而适应新的栖息地.     

高原鼠兔在不同植被覆盖的立地占据、局部灭绝和建群率研究

青藏高原的草地生态系统被野生动物和家畜广泛地利用。大型有蹄类动物的放牧和小型哺乳类动物的挖掘行为,会改变其栖息地的植物群落。基于拉萨市墨竹工卡县日多镇年村牦牛(Bos grunniens)放牧的实践,我们发现高原鼠兔(Ochotona curzoniae)立地占域率、建群和区域灭绝率与栖息地变量之间存在一定的格局关系。为了了解高原鼠兔立地占域率、建群和区域灭绝率与栖息地之间的关系,我们采用多季节性立地占据模型,利用Presence软件对相关数据进行分析。结果表明,高原鼠兔局部灭绝率与植被覆盖度之间存在正相关性,而与建群率之间则呈负相关性。     

植被覆盖度和土地利用对高原鼠兔觅食与警戒行为的影响

野生动物的自然行为受当地家畜影响。作为与家畜共享一个栖息地、并具有挖掘行为的兔形目高原鼠兔,其行为也受当地高原家畜影响。本文采用了Poisson回归分析方法,确定牦牛、不同土地利用对高原鼠兔行为频次的影响。结果显示觅食、移动频次是高原鼠兔的主要行为频次。在冬季牦牛觅食地高原鼠兔觅食行为频次高于警戒行为频次。相反,在夏季,无论是在牦牛觅食地还是在其夜宿地,高原鼠兔警戒行为的频次高于觅食行为频次。高原鼠兔行为也受不同土地利用、植被覆盖度以及季节因素的影响。植被覆盖度与觅食频次成反比,植被覆盖度高的生境高原鼠兔觅食较少,相反,植被覆盖度较低生境觅食行为频繁。另外当前牧民的定居化趋势造成局域放牧过度,加速了土地荒漠化。因此本文也认为,季节性传统游牧模式对于草地可持续发展具有重要意义。     

Foraging Patch Selection in Winter: A Balance between Predation Risk and Thermoregulation Benefit

In winter, foraging activity is intended to optimize food search while minimizing both thermoregulation costs and predation risk. Here we quantify the relative importance of thermoregulation and predation in foraging patch selection of woodland birds wintering in a Mediterranean montane forest. Specifically, we account for thermoregulation benefits related to temperature, and predation risk associated with both illumination of the feeding patch and distance to the nearest refuge provided by vegetation. We measured the amount of time that 38 marked individual birds belonging to five small passerine species spent foraging at artificial feeders. Feeders were located in forest patches that vary in distance to protective cover and exposure to sun radiation; temperature and illumination were registered locally by data loggers. Our results support the influence of both thermoregulation benefits and predation costs on feeding patch choice. The influence of distance to refuge (negative relationship) was nearly three times higher than that of temperature (positive relationship) in determining total foraging time spent at a patch. Light intensity had a negligible and no significant effect. This pattern was generalizable among species and individuals within species, and highlights the preponderance of latent predation risk over thermoregulation benefits on foraging decisions of birds wintering in temperate Mediterranean forests.     

Mammalian predator scent, vegetation cover and tree seedling predation by meadow voles

Herbivores are thought to respond to the increased risk of attack by predators during foraging activities by concentrating feeding in safe habitats and by reducing feeding in the presence of predators. We tested these hypotheses by comparing tree seedling predation by meadow voles within large outdoor enclosures treated either with scent of large mammalian predators (red fox, bobcat, coyote) or a control scent (vinegar). In addition, we compared the distribution of voles in relation to naturally occurring variation in vegetation cover and the tendency of voles to attack tree seedlings planted in small patches with cover manipulation (intact, reduced or removed cover). Predator scent did not affect the rate or spatial distribution of tree seedling predation by voles, nor did it affect giving up densities (a surrogate of patch quitting harvest rate), survival rates, body size or habitat distribution of voles. In both predator scent and vinegar treatments voles preferred abundant vegetation providing good cover, which was also the site of almost all tree seedling predation. We conclude that large mammalian predator scent does not influence the perception by voles of the general safety of habitat, which is more strongly affected by the presence of cover.     

The influence of habitat on travel speed, intermittent locomotion, and vigilance in a diurnal rodent

We studied effects of habitat structure on routine travel velocities, intermittent locomotion, and vigilance by the degu (Octodondegus), a diurnal rodent of central Chile. We predicted thattravel speed, pauses during locomotion, and vigilance wouldbe greater in open (riskier) than in shrub (safer) habitats.Video recordings of marked individuals in the wild were used to measure speed and other variables of spontaneous locomotionnot triggered by predatory attack or any other noticeable stimulusduring nonforaging periods. Time spent vigilant while foragingwas also measured. Because degus use bare-ground runways fordistant movements (e.g., between burrow openings and/or foodpatches), data on locomotion decisions were not confounded by effects of obstructive vegetation cover and/or resource abundance.When moving across the habitat between different feeding places,degus showed an intermittent pattern of locomotion, interruptingrunning events with short pauses. As predicted, travel speedand the duration of pauses between locomotion bursts were significantlygreater in open habitats. Further, the duration of locomotionbursts between feeding sites or between feeding sites and burrowswas significantly longer in open habitats. Our assumption that pauses and velocities are independent decisions was supportedby the lack of correlation between pauses and speeds duringlocomotion events. During foraging, degus devoted more timeto vigilance in open than in shrub habitats. The static positionadopted by degus during pauses, the speeds attained during movements, and the concordance between pausing behavior andvigilance across habitats suggest that pausing has an antipredatoryrole and is not limited to orientation and/or physiologicalrecovery. Our results support the view that degus perceivehigher predation risk in open areas and that flexible movement behavior reflects an adaptive antipredator response.     

Nest and foraging‐site selection in Yellowhammers Emberiza citrinella: implications for chick provisioning

Capsule Vegetation structure and invertebrate abundance interact to influence both foraging sites and nestling provisioning rate; when invertebrate availability is low, adults may take greater risks to provide food for their young.

Aims To investigate nesting and foraging ecology in a declining farmland bird whose fledging success is influenced by the availability of invertebrate prey suitable for feeding to offspring, and where perceived predation risk during foraging can be mediated by vegetation structure.

Methods Provisioning rates of adult Yellowhammers feeding nestlings were measured at nests on arable farmland. Foraging sites were compared with control sites of both the same and different microhabitats; provisioning rate was related to habitat features of foraging‐sites.

Results Foraging sites had low vegetation density, probably enhancing detection of predators, or high invertebrate abundance at high vegetation density. Parental provisioning rate decreased with increasing vegetation cover at foraging sites with high invertebrate abundance; conversely, where invertebrate abundance was low, provisioning rate increased with increasing vegetation cover.

Conclusions Vegetation structure at foraging sites suggests that a trade‐off between predator detection and prey availability influences foraging site selection in Yellowhammers. Associations between parental provisioning rate and vegetation variables suggest that where invertebrate abundance is high birds increase time spent scanning for predators at higher vegetation densities; however, when prey are scarce, adults may take more risks to provide food for their young.     

Foraging behavior of golden hamsters (<Emphasis Type="Italic">Mesocricetus auratus</Emphasis>) in the wild

Foraging theory posits that animals should maximize energy gains while minimizing risks, the largest of which is usually predation. For small burrowing mammals the best measure of risk avoidance may be the time spent in the burrow, although this measure is rarely examined. During the spring of 2005 and 2006 we recorded the foraging behavior of female golden hamsters in their natural habitat in southern Turkey. Data were collected with a data logger and by direct observations. Female golden hamsters averaged 64 min per day above ground in a series of foraging trips with a mean duration of 5.5 min. Two nursing females increased their time out of the burrow by a factor of 6–8 times over the course of 16 days by increasing both the number of trips and the length of each trip. These results show that hamsters spend little time out of the burrow, thus minimizing risk, but they also show that time spent out of the burrow is related to the energy needs of the hamsters; lactating females with high energy needs exposed themselves to much greater risk than did non-lactating females.     

Maximizing feeding efficiency and minimizing time exposed to predators: a trade-off in the black-capped chickadee

Summary Animals often must feed away from protective cover, sometimes at a considerable risk of being preyed upon. Feeding at the maximum rate while away from cover may simultaneously minimize the time spent exposed to predators, but this is not always the case. Under some circumstances, carrying prey items to protective cover before they are consumed will minimize the time spent exposed to predators, whereas feeding at maximum efficiency (staying to eat prey where they are found) will actually increase the time spent exposed to predators. Whether or not there is a conflict between maximizing foraging efficiency and minimizing exposure time, depends upon the travel time to cover relative to the handling time of a prey item; short handling times and/or long travel times are associated with the no-conflict situation, whereas the conflict situation is associated with long handling times and/or short travel times to cover. Free-ranging chickadees foraging at an artificial patch at various distances from cover can distinguish between these two foraging situations. When there is no conflict, they stay and eat at the patch. Their behavior in the conflict situation indicates that they are tradingoff foraging considerations against the risk of predation. When the cost of carrying is low and the benefit gained is high, the chickadees elect to carry items to cover; they tend to stay and eat at the patch when the relative magnitudes of costs and benefits are reversed.     

Is Foraging Time Limited During Winter? – A Feeding Experiment with Tree Sparrows Under Different Predation Risk

Small passerines are faced with a trade‐off when foraging during winter. Increasing energy reserves makes them more vulnerable to predators, while a low level of reserves exposes them to a high risk of starvation. Whether small birds under these circumstances are allowed to reduce their foraging activity under increased predation risk, for example in feeding sites more exposed to predators, remains controversial in former behavioural and ecological researches. In this study, we investigated the foraging activity of free‐living Tree Sparrow Passer montanus flocks feeding on an artificial feeding platform. The predation risk perceived by the sparrows was manipulated by placing the platform either close to or far from a bushy shelter. Foraging activity, assessed as cumulative activity of sparrows per unit time on the platform, did not differ between the low‐risk and the high‐risk conditions and did not significantly change during the day. Feeding efficiency, assessed as pecking rate, was not either reduced under the high‐risk condition. Our results suggest that sparrows were forced to feed almost continuously during the day in order to maintain their preferred level of energy reserves. However, several behavioural changes helped sparrows to adopt a safer foraging policy when feeding far from cover, as we found in another study. Altogether, sparrow flocks feeding far from cover decreased the overall foraging time (the time when any sparrow stayed on the platform) by approximately 20% as compared to the near cover condition. A possible way to maintain the same level of foraging activity despite of the reduction in overall foraging time is discussed.     

Foraging behaviour of Lesser Sheathbills Chionis minor exploiting invertebrates on a sub-Antarctic island

Summary During winter (May through October) many Lesser Sheathbills Chionis minor at Marion Island in the sub-Antarctic were obliged to leave their preferred foraging habitat in penguin colonies to forage for invertebrates on the island's coastal plain. The study describes factors affecting feeding success, time budgets and predation risk of the sheathbills which exploited these small, patchily dispersed prey. The birds appeared to select prey 1 mm in diameter, and ignore smaller, common invertebrates.Sheathbills were highly selective of foraging habitat. During 17 censuses made through the winter, 97% of the 1,504 birdsightings were at only eight of the 19 available vegetation types. Multiple regression analysis revealed that prey density was the most important criterion in habitat preference, followed by plant canopy height and distance of the habitat from the sea. These variables accounted for 78% of the variance of habitat use. Focal-animal observations in a sample of habitats showed that feeding success was correlated with prey density and distance from the sea. Tall vegetation impeded the locomotion and foraging of sheathbills. The sheathbills reduced predation risk from skuas Catharacta lonnbergi and travelling time by foraging near the shore. The spatial distribution of prey within vegetation types was apparently unimportant in habitat selection.During winter 83% of the sheathbills in the study foraged communally and 98% roosted communally. Flocks occurred only on good quality habitat and flocking probably facilitated habitat selection. Feeding success increased initially with increasing flock size but decreased in flocks greater than 15 birds, which was attributed to localized prey deletions. The sheathbills spent 88% of the daytime foraging; and feeding, looking around and walking comprised 99% of foraging time. Feeding time increased with increasing flock size, looking around decreased but walking was unaffected. Aggression was rare, was unaffected by flock size and did not significantly affect feeding. A probability model showed that sheathbills could greatly reduce predation risk by flocking but the benefits would not improve much in flocks greater than eight birds.The habitat selection, time budgets and feeding success of adults, subadults and juveniles were very similar.The exploitation of terrestrial invertebrates by sheathbills was interpreted as an expansion of the population's trophic niche to tap an underexploited resource on a species-poor island.     

Foraging strategies of an insectivorous marsupial,Sminthopsis youngsoni (Marsupialia: Dasyuridae), in Australian sandridge desert

This study investigated the effects of predation risk, dune position and microhabitat on foraging of the Lesser Hairy‐footed Dunnart Sminthopsis youngsoni, a small insectivorous marsupial, in the Simpson Desert of western Queensland. The intensity of foraging was assessed by establishing feeding stations (dishes containing mealworms) in open and bush microhabitats at three levels on sand dunes, and recording the numbers of prey taken by dunnarts from the stations after nightly bouts of foraging. Risk of predation was manipulated by provision of artificial illumination at alternate feeding stations on each of five occasions when trials were run. The numbers of mealworms left after feeding bouts varied inconsistently across trials, providing little evidence that dunnarts respond to habitat or predation risk while foraging. These results contrast sharply with studies of arid zone rodents, where foraging is usually sensitive to both predation risk and resource distribution. We suggest that S. youngsoni forages equally in all habitats of its sandridge environment, and experiences relatively low risk of predation whilst doing so.