Assessment of scale-dependent foraging behaviour in southern elephant seals incorporating the vertical dimension: a development of the First Passage Time method

1. Identifying the spatial scales at which top marine predators forage is important for understanding oceanic ecosystems. Several methods quantify how individuals concentrate their search effort along a given path. Among these, First-Passage Time (FPT) analysis is particularly useful to identify transitions in movement patterns (e.g. between searching and feeding). This method has mainly been applied to terrestrial animals or flying seabirds that have little or no vertical component to their foraging, so we examined the differences between classic FPT and a modification of this approach using the time spent at the bottom of a dive for characterizing the foraging activity of a diving predator: the southern elephant seal. 2. Satellite relayed data loggers were deployed on 20 individuals during three successive summers at the Kerguelen Islands, providing a total of 72 978 dives from eight juvenile males and nine adult females. 3. Spatial scales identified using the time spent at the bottom of a dive ( = 68.2 +/- 42.1 km) were smaller than those obtained by the classic FPT analysis ( = 104.7 +/- 67.3 km). Moreover, foraging areas identified using the new approach clearly overlapped areas where individuals increased their body condition, indicating that it accurately reflected the foraging activity of the seals. 4. These results suggest that incorporating the vertical dimension into FPT provides a different result to the surface path alone. Close to the Antarctic continent, within the pack-ice, sinuosity of the path could be explained by a high sea-ice concentration (restricting elephant seal movements), and was not necessarily related to foraging activity. 5. Our approach distinguished between actual foraging activity and changes in behaviour induced by the physical environment like sea ice, and could be applied to other diving predators. Inclusion of diving parameters appears to be essential to identify the spatial scale of foraging areas of diving animals.     

Submarine foraging behavior of alcids in an artificial environment

We used an artificial environment at Sea World, Inc, San Diego, to study underwater foraging behavior of alcids. Larger birds dove longer and had greater wingbeat frequencies. The pigeon guillemot Cepphus columba was the only species to use both feet and wings for propulsion; all others used just wings. Aggressive interactions underwater were common. Competition among alcids in the wild may occur primarily underwater, and artificial environments may be the best means to study such interactions.     

Marine foraging ecology influences mercury bioaccumulation in deep-diving northern elephant seals

Mercury contamination of oceans is prevalent worldwide and methylmercury concentrations in the mesopelagic zone (200–1000 m) are increasing more rapidly than in surface waters. Yet mercury bioaccumulation in mesopelagic predators has been understudied. Northern elephant seals (Mirounga angustirostris) biannually travel thousands of kilometres to forage within coastal and open-ocean regions of the northeast Pacific Ocean. We coupled satellite telemetry, diving behaviour and stable isotopes (carbon and nitrogen) from 77 adult females, and showed that variability among individuals in foraging location, diving depth and δ¹³C values were correlated with mercury concentrations in blood and muscle. We identified three clusters of foraging strategies, and these resulted in substantially different mercury concentrations: (i) deeper-diving and offshore-foraging seals had the greatest mercury concentrations, (ii) shallower-diving and offshore-foraging seals had intermediate levels, and (iii) coastal and more northerly foraging seals had the lowest mercury concentrations. Additionally, mercury concentrations were lower at the end of the seven-month-long foraging trip (n = 31) than after the two-month- long post-breeding trip (n = 46). Our results indicate that foraging behaviour influences mercury exposure and mesopelagic predators foraging in the northeast Pacific Ocean may be at high risk for mercury bioaccumulation.     

The influence of preceding dive cycles on the foraging decisions of Antarctic fur seals

The foraging strategy of many animals is thought to be determined by their past experiences. However, few empirical studies have investigated whether this is true in diving animals. We recorded three-dimensional movements and mouth-opening events from three Antarctic fur seals during their foraging trips to examine how they adapt their behaviour based on past experience—continuing to search for prey in the same area or moving to search in a different place. Each dive cycle was divided into a transit phase and a feeding phase. The linear horizontal distance travelled after feeding phases in each dive was affected by the mouth-opening rate during the previous 244 s, which typically covered two to three dive cycles. The linear distance travelled tended to be shorter when the mouth-opening rate in the previous 244 s was higher, i.e. seals tended to stay in the same areas with high prey-encounter rates. These results indicate that Antarctic fur seals follow decision-making strategies based on the past foraging experience over time periods longer than the immediately preceding dive.     

蜜蜂采集及其信息传递的行为机制研究进展

蜜蜂的采集行为是蜜蜂众多社会行为中一种较复杂的行为,涉及信息评估、信息传递、学习记忆及能量代谢等不同的行为过程。研究蜜蜂采集及信息交流系统的分子机制,不仅利于蜜蜂的理论研究和蜂产业的发展,还为人类语言及信息交流系统的研究提供借鉴。本文从行为、感觉基础及分子机制等不同研究层面,综述了近年来对蜜蜂采集及信息传递行为的研究进展,并提出了研究设想,以期为深入研究蜜蜂的采集行为及其信息传递行为的分子机制提供参考。     

蜜蜂花粉采集行为的调控机制

蜜蜂Apisspp.是一种社会性昆虫。社会性昆虫在对它们群体自身数量和巢穴环境的调节方面表现出明显的稳态特点,Emerson将这种稳态调节称为社会性稳态。蜂群中花粉的储存量就具有稳态的特点。蜂群的花粉采集行为是由蜂群对花粉的需要决定的。关于蜜蜂花粉采集行为的调控机制,目前的研究主要集中于是哪些信息以及蜂群是如何识别这些信息从而调控其采粉行为,主要形成了直接识别和间接识别2种假说。对这2种假说进行综述。     

Optimal diving behaviour for foraging in relation to body size

Overall, large animals dive longer and deeper than small animals; however, after the difference in body size is taken into account, smaller divers often tend to make relatively longer dives. Neither physiological nor theoretical explanations have been provided for this paradox. This paper develops an optimal foraging diving model to demonstrate the effect of body size on diving behaviour, and discusses optimal diving behaviour in relation to body size. The general features of the results are: (1) smaller divers should rely more heavily on anaerobic respiration, (2) larger divers should not always make longer dives than smaller divers, and (3) an optimal body size exists for each diving depth. These results explain the relatively greater diving ability observed in smaller divers, and suggest that if the vertical distribution of prey in the water column is patchy, there is opportunity for a population of diving animals to occupy habitat niches related to body size.     

Successful foraging zones of southern elephant seals from the Kerguelen Islands in relation to oceanographic conditions

Southern elephant seals, Mirounga leonina, undertake large-scale oceanic movements to access favourable foraging areas. Successful foraging areas of elephant seals from the Kerguelen Islands are investigated here in relation to oceanographic parameters. Movements and diving activity of the seals as well as oceanographic data were collected through a new generation of satellite relayed devices measuring and transmitting locations, pressure, temperature and salinity. For the first time, we have associated foraging behaviour, determined by high increased sinuosity in tracks, and dive density (i.e. number of dives performed per kilometre covered), and changes in body condition, determined by variations in drift rate obtained from drift dives, to identify the oceanographic conditions of successful foraging zones for this species. Two main sectors, one close to the Antarctic continent and the other along the Polar Front (PF), where both foraging activity and body condition increase, seem to be of particular interest for the seals. Within these regions, some seals tended to focus their foraging activity on zones with particular temperature signatures. Along the Antarctic continent, some seals targeted colder waters on the sea bottom during benthic dives, while at the PF the favourable zones tended to be warmer. The possible negative effect of colder waters in Antarctic on the swimming performances of potential fish or squid prey could explain the behaviour of elephant seals in these zones, while warmer waters within the PF could correspond to the optimal conditions for potential myctophid prey of elephant seals.     

Structure and foraging behavior in hypogean crustacean assemblages

Varying assemblages of three crustaceans and their behavioral interactions were studied in Rice Cave during eight visits over a two year period. The assemblages of crustaceans observed were seen to depend primarily on periodic invasions into the cave byGammarus troglophilus, low resource levels, habitat preference, the sensitivity ofCaecidotea stygia to disturbance, and subterranean adaptation by the troglobites.Both the troglophilG. troglophilus and the troglobite,C. stygia preferred mud and gravel bottomed pools. The more active and aggressiveG. troglopholus when at high densities eliminatedC. stygia from preferred habitat and baited food placed in it.Bactrurus brachycaudus, a troglobite, preferred riffles, but was able to compete for baited food withG. troglophilus by virtue of its larger size and similar behaviors. When onlyC. stygia was present at baited sites access to food was size-related with a rotation of large and small individuals on and off the bait occurring.     

Locomotion in diving elephant seals: physical and physiological constraints

To better understand how elephant seals (Mirounga angustirostris) use negative buoyancy to reduce energy metabolism and prolong dive duration, we modelled the energetic cost of transit and deep foraging dives in an elephant seal. A numerical integration technique was used to model the effects of swim speed, descent and ascent angles, and modes of locomotion (i.e. stroking and gliding) on diving metabolic rate, aerobic dive limit, vertical displacement (maximum dive depth) and horizontal displacement (maximum horizontal distance along a straight line between the beginning and end locations of the dive) for aerobic transit and foraging dives. Realistic values of the various parameters were taken from previous experimental data. Our results indicate that there is little energetic advantage to transit dives with gliding descent compared with horizontal swimming beneath the surface. Other factors such as feeding and predator avoidance may favour diving to depth during migration. Gliding descent showed variable energy savings for foraging dives. Deep mid-water foraging dives showed the greatest energy savings (approx. 18%) as a result of gliding during descent. In contrast, flat-bottom foraging dives with horizontal swimming at a depth of 400m showed less of an energetic advantage with gliding descent, primarily because more of the dive involved stroking. Additional data are needed before the advantages of gliding descent can be fully understood for male and female elephant seals of different age and body composition. This type of data will require animal-borne instruments that can record the behaviour, three-dimensional movements and locomotory performance of free-ranging animals at depth.     

A life in the fast lane: energetics and foraging strategies of the great cormorant

Body insulation is critically important for diving marine endotherms. However,cormorants have a wettable plumage, which leads to poor insulation. Despitethis, these birds are apparently highly successful predatorsin most aquatic ecosystems. We studied the theoretical influenceof water temperature, dive depth, foraging techniques, and preyavailability on the energetic costs of diving, prey search time,daily food intake, and survival in foraging, nonbreeding greatcormorants (Phalacrocorax carbo). Our model was based on fieldmeasurements and on data taken from the literature. Water temperatureand dive depth influenced diving costs drastically, with predicted increasesof up to 250% and 258% in males and females, respectively. Changes inwater temperature and depth conditions may lead to an increaseof daily food intake of 500-800 g in males and 440-780 g infemales. However, the model predicts that cormorant foragingparameters are most strongly influenced by prey availability,so that even limited reduction in prey density makes birds unableto balance energy needs and may thus limit their influence onprey stocks. We discuss the ramifications of these results withregard to foraging strategies, dispersal, population dynamics,and intraspecific competition in this avian predator and pointout the importance of this model species for our understandingof foraging energetics in diving endotherms.     

捕食风险及其对动物觅食行为的影响

对捕食风险的涵义及其对猎物动物觅食行为的影响、猎物动物面对捕食风险时的反应进行了论述。捕食风险可以简单地理解为一定时间内猎物动物被杀死的概率。当捕食风险存在时 ,动物会选择相对安全但觅食效益较低的地点觅食 ;由于死亡率和消化方面的限制 ,一般都会产生食谱收缩 ;觅食活动方式的时间格局也会因捕食风险而发生改变 ,如水生动物的昼夜垂直迁移、某些陆生动物昼行性与夜行性活动的转换、月光回避等。在与捕食者发生遭遇时 ,猎物动物的主要反应是 :①发出某些信号以阻止捕食者的追捕 ;②靠近并注视捕食者 ;③逃逸 ;④在一定的时间恢复觅食活动。在以往的研究中 ,对捕食者种类已经有了较多的了解 ,而对猎物如何判断捕食者丰富度信息、估计风险程度等方面则知之甚少 ;同时 ,对捕食风险水平的调控、对多种因素的综合分析也较少涉及。在今后的研究中 ,还应该考虑研究的尺度问题 ,因为在不同尺度的环境条件下 ,猎物动物对于捕食风险的反应可能大相径庭。     

Physiology and behavior influence lactation efficiency in northern elephant seals (Mirounga angustirostris)

The efficiency with which mothers convert acquired energy into milk is a key determinant of the magnitude of parental investment in mammals; however, the mechanisms underlying lactation efficiency are poorly understood. Investigations on northern elephant seals have shown lactation efficiency, measured as the proportion of total energy expenditure that goes to the pup as milk, increases with age. In a cross-sectional study the physiological and behavioral determinants of lactation efficiency were investigated in eight young and seven prime (older) elephant seals by conducting behavioral observations and collecting milk, blood, and tissue on days 3 and 22 of lactation. Milk composition, circulating fatty acid and triglyceride concentrations, and mammary and blubber lipoprotein lipase activity were determined. Prime females had significantly greater percent milk fat and circulating fatty acids on day 3 than did young females, but these differences disappeared by day 22. The ability for prime females to produce higher-energy milk early in lactation may allow them to increase lactation efficiency by increasing the rate of energy transfer. In addition, prime females spent significantly more time resting. A combination of reduced activity and more rapid energy delivery likely explains the increase in lactation efficiency with age found in a previous study.     

Female competition and reproductive success in northern elephant seals

The probability of weaning a healthy pup increases with age in female northern elephant seals, Mirounga angustirostris. On Año Nuevo Island, California, weaning success among ‘prime’ females, those 6 years of age or older, was more than double that of ‘young’ females, those 3 to 5 years old. Prime females were better mothers than young females because of superior size, higher social dominance, and greater maternal experience; they were more likely to mate with high-ranking males and gave birth at an optimal time and place, circumstances that maximized the probability that their pups would survive, develop, and reproduce. The competitive advantage of prime-age mothers over younger ones was greatest when female and pup density was high. Young females improved their chances of reproducing successfully by emigrating from crowded harems and establishing new colonies.     

Species-specific foraging behavior of birds in a riparian forest

In riparian forest, insectivorous birds are largely dependent on aquatic preys. However, the contribution made by aquatic preys to bird diets varies considerably among bird species. In the present study, bird foraging behaviors were observed in order to examine the relationship between bird foraging method and the variation in the contribution of aquatic preys. The great tit, the black-faced bunting, and the wren are largely dependent on aquatic preys by capturing them on the ground. Sallyers, the brown flycatcher, the pale-legged willow warbler, and the narcissus flycatcher are also largely dependent on aquatic preys and capture them mostly during flight. The narcissus flycatcher frequently utilises aquatic invertebrates dwelling on the ground. The leaf and branch gleaner, the crowned willow warbler, does not depend on aquatic prey as much. Although both the pygmy woodpecker and nuthatch are branch and trunk gleaners, the nuthatch utilises aquatic preys frequently by capturing them on the ground as well as during flight, but the pygmy woodpecker does not depend on aquatic preys. The marsh tit also does not depend on aquatic preys but carefully searches terrestrial prey that hide in the vegetation. The differential dependence on aquatic preys among species can lead to the heterogeneous distribution of birds within a riparian forest, suggesting that the indirect effect of aquatic preys on a forest ecosystem via birds can vary within a forest–stream ecotone.     

A variable-response model for parasitoid foraging behavior

An important factor inducing variability in foraging behavior in parasitic wasps is experience gained by the insect. Together with the insect's genetic constitution and physiological state, experience ultimately defines the behavioral repertoire under specified environmental circumstances. We present a conceptual variable-response model based on several major observations of a foraging parasitoid's responses to stimuli involved in the hostfinding process. These major observations are that (1) different stimuli evoke different responses or levels of response, (2) strong responses are less variable than weak ones, (3) learning can change response levels, (4) learning increases originally low responses more than originally high responses, and (5) hostderived stimuli serve as rewards in associative learning of other stimuli. The model specifies how the intrinsic variability of a response will depend on the magnitude of the response and predicts when and how learning will modify the insect's behavior. Additional hypotheses related to the model concern how experience with a stimulus modifies behavioral responses to other stimuli, how animals respond in multistimulus situations, which stimuli act to reinforce behavioral responses to other stimuli in the learning process, and finally, how generalist and specialist species differ in their behavioral plasticity. We postulate that insight into behavioral variability in the foraging behavior of natural enemies may be a help, if not a prerequisite, for the efficient application of parasitoids in pest management.     

Asset protection in juvenile salmon: how adding biological realism changes a dynamic foraging model

The "asset-protection principle" created by Clark is based ona dynamic programming model and states that individuals should(1) become more averse to predation risk as they accumulatefitness assets but (2) generally be more willing to acceptpredation risk later in the foraging season. To test whetherthese predictions hold under biologically meaningful foraging parameters, I constructed a dynamic model of the optimal trade-offbetween foraging and predator avoidance in juvenile salmon.The model incorporates temperature and body-size dependentbio-energetic constraints typical for juvenile fish, whichgrow by orders of magnitude over a season. In its simplestform using seasonally constant growth potential and a linear over-winter survival function, my results equal those of Clark'smodel. Adding a fitness function and environmental data fromfield studies accentuates the asset-protection effect and fundamentallychanges the seasonal pattern of optimal effort. Simulationof typical poor feeding conditions in mid-summer yields theprediction of increased foraging in the spring in anticipationof worsening conditions. Increasing overall predation riskresults in smaller fish at the end of the season with a trade-offbetween summer and winter survival. The model generates testablepredictions for juvenile salmon and provides insights for otherorganisms (particularly poikilotherms) that are subject tosize-dependent or seasonally changing foraging dynamics.