Mortality by moonlight: predation risk and the snowshoe hare

Optimal behavior theory suggests that prey animals will reduceactivity during intermittent periods when elevated predationrisk outweighs the fitness benefits of activity. Specifically,the predation risk allocation hypothesis predicts that preyactivity should decrease dramatically at times of high predationrisk if there is high temporal variation in predation risk butshould remain relatively uniform when temporal variation inpredation risk is low. To test these predictions we examinedthe seasonably variable response of snowshoe hares to moonlightand predation risk. Unlike studies finding uniform avoidanceof moonlight in small mammals, we find that moonlight avoidanceis seasonal and corresponds to seasonal variation in moonlightintensity. We radio-collared 177 wild snowshoe hares to estimatepredation rates as a measure of risk and used movement distancesfrom a sample of those animals as a measure of activity. Inthe snowy season, 5-day periods around full moons had 2.5 timesmore predation than around new moons, but that ratio of theincreased predation rate was only 1.8 in the snow-free season.There was no significant increase in use of habitats with morehiding cover during full moons. Snowshoe hares' nightly movementdistances decreased during high-risk full-moon periods in thesnowy season but did not change according to moon phase in thesnow-free season. These results are consistent with the predationrisk allocation hypothesis.     

Observations on the feeding, growth rate and habits of newly settled Octopus cyanea

This paper records observations on the behaviour of Octopus cyuneu caught in Hawa shortly after settlement from the plankton. The young animals rapidly establish "homes" on the bottom and defend these against their own species. Of a variety of food offered, crabs were most frequently (nearly always) taken; the animals always took the prey home to eat it. Records of diurnal activity show morning and evening peaks as in adults. There was a steady 2–3.5% daily increase in weight over the first six months (July-January) after settlement     

Does prey capture induce area-restricted search? A fine-scale study using GPS in a marine predator, the wandering albatross

In a patchy environment, predators are expected to increase turning rate and start an area-restricted search (ARS) when prey have been encountered, but few empirical data exist for large predators. By using GPS loggers with devices measuring prey capture, we studied how a marine predator adjusts foraging movements at various scales in relation to prey capture. Wandering albatrosses use two tactics, sit and wait and foraging in flight, the former tactic being three times less efficient than the latter. During flight foraging, birds caught large isolated prey and used ARS at scales varying from 5 to 90 km, with large-scale ARS being used only by young animals. Birds did not show strong responses to prey capture at a large scale, few ARS events occurred after prey capture, and birds did not have high rates of prey capture in ARS. Only at small scales did birds increase sinuosity after prey captures for a limited time period, and this occurred only after they had caught a large prey item within an ARS zone. When this species searches over a large scale, the most effective search rule was to follow a nearly straight path. ARS may be used to restrict search to a particular environment where prey capture is more predictable and profitable.     

The feeding behaviour of New Zealand Dolomedes species (Araneae: Pisauridae)

Abstract

The prey spectrum and predatory behaviour of Dolomedes sp. (‘D. III’), D. aquaticus, and D. minor are described from a series of field and laboratory investigations, the former made around Nelson and on Banks Peninsula, Canterbury, during summer months. All species are large, robust spiders that capture prey by directly seizing it in their mouthparts, not using silk at any stage of predation. Adult aquatic insects are their main prey, but these are available only irregularly during their activity period (night-time), and the spiders are opportunistic in their feeding habits. They will eat virtually any available small animal, and at least the largest species, D. III, is able to capture and ingest small fishes. Dead as well as live organisms are taken. Furthermore, the spiders are capable of feeding infrequently; when feeding on small prey organisms they may capture several sequentially, to increase the size of the meal. Live prey is caught while it is in flight, or on the ground, or at the water surface (rarely submerged), and is detected primarily by touch and airborne sound; vision is unnecessary for normal predation. Prey is captured very rapidly, even though this may initially involve a dash of up to 40 cm across the water surface to locate the organism. Stages in the behaviour of an active spider, from waiting for prey to grooming after ingestion, are described.     

Predation by domestic cats in an English village

We studied predation by approximately 70 domestic cats ( Felis catus L.) in the Bedfordshire village of Felmersham over a one-year period. All the prey items brought home by virtually all the cats in the village were recorded and, where possible, identified. A total of 1090 prey items (535 mammals, 297 birds and 258 unidentified animals) were taken, an average of about 14 per cat per year. Twenty two species of birds and 15 species of mammals were identified. The most important items were woodmice (17%), house sparrows (16%) and bank voles (14%).
Old cats of both sexes caught fewer prey over the year than young cats. Female cats on the edge of the village also caught more prey than female cats in intermediate or central areas of the village; male cats showed no such effect. The type of prey caught also varied with position in the village; 'core' cats caught proportionately more birds than 'edge' cats. There was some indication in the data that cats caught fewer prey in areas where cat density was highest, but this effect was impossible to disentangle from position in the village. Weather apparently influenced hunting success. Temperature had no direct influence, but fewer prey were caught in winter; cats also caught less on wet days and windy days.
Estimates of the number of house sparrows in the village at the start of the breeding season, and the number of sparrows known to have been caught by the cats, suggest that at least 30% of the sparrow deaths in the village were due to cats. Domestic cats would appear to be major predators in this typical English village.     

Fear and lethality in snowshoe hares: the deadly effects of non‐consumptive predation risk

Predators play a critical, top–down role in shaping ecosystems, driving prey population and community dynamics. Traditionally, studies of predator‐prey interactions have focused on direct effects of predators, namely the killing of prey. More recently, the non‐consumptive effects of predation risk are being appreciated; e.g. the ‘ecology of fear’. Prey responses to predation risk can be morphological, behavioural, and physiological, and are assumed to come at a cost to prey fitness. However, few studies have examined the relationship between predation risk and survival in wild animals. We tested the hypothesis that predation risk itself could reduce survival in wild‐caught snowshoe hares. We exposed female snowshoe hares to a simulated predator (a trained dog) during gestation only, and measured adult survival and, in surviving females, their ability to successfully wean offspring. We show for the first time in a wild mammal that the risk of predation can itself be lethal. Predation risk reduced adult female survival by 30%, and had trans‐generational effects, reducing offspring survival to weaning by over 85% – even though the period of risk ended at birth. As a consequence of these effects the predator‐exposed group experienced a decrease in number, while the control group substantially increased. Challenges remain in determining the importance of risk‐induced mortality in natural field settings; however, our findings show that non‐lethal predator encounters can influence survival of both adults and offspring. Future work is needed to test these effects in free‐living animals.     

Prey Size Selection under Simultaneous Choice by the Broad-Headed Skink (Eumeces laticeps)

Diet selection among several prey types present in a dense aggregation, permitting a predator to become satiated without changing patches, may be important for predators that can eat many small prey items in a single bout. Choice in this scenario differs from that in optimal foraging models for sequential diet choice model and simultaneous choice models when travel time between patches is needed. Furthermore, satiation and depletion effects may be important in dense prey aggregations. We predicted that in dense prey aggregations, predators should eat the most profitable prey first, switching to smaller prey as larger ones become depleted and predators become satiated, and that prey below some minimum profitability should be rejected. When large numbers of prey of varying sizes were presented simultaneously, broad‐headed skinks (Eumeces laticeps) preferentially consumed large crickets, ate some medium‐sized crickets late in ingestion sequences, but ate no small crickets. Prey depletion, with selection of the currently most profitable prey type, appears to account for much of observed prey switching, and satiation may contribute. When four crickets of each of four sizes were presented, lizards ate largest first, then medium‐sized. Some then ate small crickets, but none ate very small crickets. These observations and exclusion of small crickets from the diet by many lizards when larger ones were unavailable support the predictions. In tests with three sizes of juvenile mice presented singly, the smallest were attacked at shortest latency and eaten, medium‐sized mice were attacked at greater latency but could not be subdued, and large mice were not attacked. These data suggest that as prey become too large to subdue and eat readily, profitability declines until they are excluded from the diet. Unsuccessful attacks on medium‐sized mice suggest that lizards had to learn their own capabilities with respect to a novel prey type.     

Use of the immunofluorescence method in an epidemic focus of tularaemia

Four hares found dead and 32 animals (small rodents, weasels, deer) caught in a focus of tularaemia were examined by the immunofluorescence method. In full agreement with the biological test, the use of fluorescent antibodies showed the presence ofPasteurella tularensis in the hares, even when the organs were massively contaminated with other bacteria, making cultivation tests quite impossible. In the other animals, all the test methods gave negative results. Tests of sera from 149 convalescent patients and 59 control subjects showed complete agreement (positivity or negativity) between the indirect immunofluorescence method and the agglutination reaction. The question of the titres found in the indirect immunofluorescence reaction are discussed. The first results with the use of fluorescent antibodies in practice thus confirm that this is a suitable method for examining animals in epizootic foci and for detecting specific antibodies in human serum.     

Factors influencing the hunting success of the predator: A model with sighthounds

Using microbiological criteria (the number of CFU in nose prints on agar medium), it has been shown that the proportion of individuals with a high CFU count is significantly higher among brown hares caught by sighthounds or exposed to immobilization stress than among shot hares. A hypothesis is proposed that metabolites of the body surface microflora in animals exposed to long-term stress account for their specific stress odor. Observations on wild hare coursing with the use of GPS tracking (1-s update rate) provide evidence that hunting success is not directly dependent on the absolute and relative coursing speeds, the number of sighthounds, and the distance, duration, and number of coursing episodes. An analysis has been performed of stress odor as a universal criterion allowing the predator to estimate the vulnerability of potential prey. Selective elimination of unhealthy (stressed) individuals by predators is a mechanism of natural selection for increased adaptation of populations and species to the effects of a broad spectrum of environmental factors.     

Behavioral responses to a change in stimulus: transport vs. attack behavior in a carnivorous land snail, Haplotrema concavum

Abstract. Haplotrema concavum , a carnivorous land snail, responds differently to the same prey when hunting versus when transporting food. The ability of these animals to distinguish between fresh, unmanipulated or uneaten prey and manipulated or partially eaten prey was tested by switching prey items while the predator was in the process of transporting the prey. Predators responded to a switch from a manipulated egg of Anguispira alternata to an unmanipulated egg by suspending transport behavior while the new egg was manipulated. Seven of ten predators responded to a switch from an egg of A. alternata to a conspecific ( H. concavum ) egg by stopping transport and abandoning the less-preferred food. Predators responded to a switch from partially eaten hatchlings of A. alternata to fresh but injured hatchlings by stopping transport after the retrieval stage to eat the new hatchling, after which transport was resumed. Predators which were not engaged in transport behavior attacked rather than retrieved fresh, injured hatchling prey. These results suggest that by manipulating its prey, the predator alters the sensory stimulus of the prey by marking the prey with predator mucus which, in turn, elicits the transport behavior by the predatory snail.     

How should a clever baboon choose and move rocks?

Chacma baboons (Papio ursinus) intentionally overturn rocks to feed on the invertebrates beneath. However, baboons do not move all the rocks they encounter, with this presumably reflecting cost–benefit (or effort–reward) trade‐offs in their foraging behavior. We ask, how do “clever baboons” choose rock sizes and shapes and move these rocks? Using optimal foraging theory, we predicted that baboons would prefer to move medium‐sized rocks, a trade‐off between moving larger rocks that might require more effort to move, and smaller rocks that likely do not provide enough prey (the reward) to make the effort worthwhile. We also expected baboons to prefer rounded rocks as these will require less energy to move by rolling (rather than being flipped as for flat rocks) and that the effort of rock movement might be offset by moving rocks along the shortest axis. We show that baboons have clear preferences for specific rock sizes (medium‐sized) and shapes (angular and flat when these were medium‐sized), and the way in which rocks are moved (along the shortest axis). Prey occurred infrequently under rocks. The low predictability of prey beneath rocks suggests that such prey, when encountered, is of considerable value to baboons for them to expend the search effort, and also explains the extensive nature of rock movement by baboons in the landscape. Our study provides a novel application of the optimal foraging theory concept and has important implications for understanding and predicting how animals choose to move rocks.     

Diet,nesting density,and breeding success of rough-legged buzzards (Buteo lagopus) on the Nenetsky Ridge,Arctic Russia

The rough-legged buzzard, a circumpolar avian predator, is usually defined as rodent specialist in the tundra but as a generalist in the boreal zone, leaving open the question of where the shift in feeding strategy occurs. Here, we investigated the diet and breeding biology of buzzards as well as abundance of their possible prey during 5 years in the low-Arctic shrub tundra on the Nenetsky Ridge, Russia. We employed three complementary methods to assess the diet of this Arctic predator—pellet dissection, identification of prey remains on nests, and stable isotope analysis—to overcome their respective limitations. We documented fluctuations in abundances of the likely prey, namely rodents, ptarmigans, and hares. Nesting density of buzzards changed substantially over the years, but did not track the abundance cycle of the rodents. The number of buzzard fledglings was relatively low (1.08 ± 0.3) and did not change according to the density of rodents. In the year when rodents were at their lowest abundance, diet analyses of nestlings documented a shift from rodents to alternative prey, with a decrease in the proportion of tundra voles and an increase in proportion of hares, ptarmigans, and ducks. Here, we argue that buzzards may adopt different feeding strategies along the gradient from generalists to specialists. While the rough-legged buzzard is usually considered a small rodent specialist, our study shows that it can shift to alternative prey where or when rodents are scarce and when alternative prey are sufficiently abundant to provide subsistence for breeding.     

Do plant secondary compounds determine feeding preferences of snowshoe hares?

Summary We investigated the food preferences of captive snowshoc hares (Lepus americanus) in winter to test three hypotheses proposed to explain food choices by hares: (1) that food choice is related to the protein content of twigs; 92) that defensive chemicals present in twigs are negatively correlated with hare food preferences; and (3) that hares eat less-preferred but protein-rich twigs when their diet is buffered by large amounts of palatable food. Hares exhibited striking and consistent preferences for different species and, in general, preferred mature twigs to juvenile growth stages. Preferences across species among mature twigs were not, however, the same as preferences for juvenile growth stages across species. None of the three hypotheses adequately explained food choice by hares. Hares did not (1) select twigs that were high in protein content. They also did not (2) consistently select twigs that were low in resins or phenols. Finally (3), hares generally ate less, not more of non-preferred twigs in the presence of a protein and energy rich alternative food, commercial rabbit chow. Food preferences of hares must presumably have some chemical basis, but no simple theory has yet explained what this is. We suggest that hares may not be under severe dietary constraints imposed by chemical defenses in winter.     

First evidence of prey capture and meat eating by wild Yunnan snub-nosed monkeys Rhinopithecus bieti in Yunnan,China

Most extant nonhuman primates occasionally prey on fast-moving, warm-blooded animals; however, Indriidae, Lepilemuridae, and Colobinae either scavenged for meat or did not eat meat at all. Here we report six cases of animal consumption by the snub-nosed monkey Rhinopithecus bieti in a wild, habituated group between 2004 and 2009 in Yunnun, China. At present,only males in an all-male unit within the study group were involved in active hunting. Such a male-biased activity may be related to the group structure and spatial spread of R. bieti. Two females were observed eating freshly killed birds. The findings confirmed that R. bieti engaged in scavenging and, when hunting, employed a cranio-cervical bite to kill their prey. Meat eating is likely a nutrient maximization feeding strategy in R. bieti, especially in males. A begging behavior occurred after successful prey capture. Although begging was observed, no sharing of the meat was seen. The present findings illuminate the dietary diversity of R. bieti and their ability to expand their dietary spectrum.     

Small-scale spatial variability in the diet of pampas foxes (<Emphasis Type="Italic">Pseudalopex gymnocercus</Emphasis>) and human-induced changes in prey base

Predators display functional responses to variation in prey availability that result in dietary distinction at different spatial scales. Such differentiation can be enhanced when human-induced changes in land use increase spatial heterogeneity in prey availability. This has been recorded for canids, but available information is skewed to regional scales. Further, though human activities have strongly altered neotropical biomes, knowledge about small-scale dietary differentiation of canids come mainly from holartic species. Thus, we quantified variability in the diet of a ubiquitous South American canid species (i.e., the pampas fox, Pseudalopex gymnocercus) over a relatively small area of grasslands in Argentina, comparing its diet at three close sampling sites varying in human disturbance. We found that small-scale dietary differentiation was influenced by human-induced habitat modifications, both directly by local subsidizing of introduced prey (e.g., livestock carrion and hares) and indirectly by altering the availability of native prey. Overall, pampas foxes seemed to be highly flexible in their trophic ecology, being able to cope with marked habitat alterations and likely benefiting from food cross-subsidizing from agricultural landscape to protected grassland relicts. This has implications for management and conservation purposes, and highlights the importance of quantifying variability in foraging behavior of carnivores over small spatial scales.     

Diet variation of common buzzards in Finland supports the alternative prey hypothesis

The regional synchrony of short-term population fluctuations of small rodents and small game has usually been explained by varying impacts of generalist predators subsisting on both voles and small game (the "alternative prey hypothesis" APH). APH says that densities of predators increase as a response to increasing vole densities and then these predators shift their diet from the main prey to the alternative prey when the main prey decline and vice versa. We studied the diet composition of breeding common buzzards Buteo buteo during 1985-92 in western Finland. Microtus voles were the main prey and water voles, shrews, forest grouse, hares and small birds the most important alternative prey. Our data from the between-year variation in the diet composition of buzzards fulfilled the main predictions of APH. The yearly proportion of main prey (Microtus voles) in the diet was higher in years of high than low vole abundance. The proportion of grouse in the diet of buzzards was negatively related to the abundance of Microtus voles in the field and was nearly independent of grouse abundance in the field. In addition, buzzards mainly took grouse chicks and young hares which is consistent with the prediction of APH. Therefore, we conclude that buzzards are able to shift their diet in the way predicted by the APH and that buzzards, together with other generalist predators, may reduce the breeding success of small game in the decline phase of the vole cycle, and thus substantially contribute to the existence of short-term population cycles of small game.     

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。     

Notes on the ecology of a suburban population of Rainbow lizards in coastal Kenya

Aspects of the ecology of a suburban population of rainbow lizards, Agama agama Linnaeus 1758, have been studied in Malindi, a coastal locality of SE Kenya. Four different family groups were monitored on a wall transect 120 m long. Each group constituted a dominant male (i.e. a brightly coloured and aggressive individual) and three to four adult females, but in one of the studied groups a subordinate male was also seen. Both sexes were active in the morning, and peak activity fell between 10.00 and 11.30 hours. Dominant males used elevated perches significantly more often than subordinate males and females. The diet consisted of terrestrial arthropods, and most of the prey eaten were beetles (6–8 mm long). The foraging strategy used by rainbow lizards was to eat small insects at very short time intervals. The lizards used sit-and-wait foraging, remaining motionless until the prey was <5 cm away. The rainbow lizards studied did not feed upon plant material.     

Implications of shared predation for space use in two sympatric leporids

Spatial variation in habitat riskiness has a major influence on the predator–prey space race. However, the outcome of this race can be modulated if prey shares enemies with fellow prey (i.e., another prey species). Sharing of natural enemies may result in apparent competition, and its implications for prey space use remain poorly studied. Our objective was to test how prey species spend time among habitats that differ in riskiness, and how shared predation modulates the space use by prey species. We studied a one‐predator, two‐prey system in a coastal dune landscape in the Netherlands with the European hare (Lepus europaeus) and European rabbit (Oryctolagus cuniculus) as sympatric prey species and red fox (Vulpes vulpes) as their main predator. The fine‐scale space use by each species was quantified using camera traps. We quantified residence time as an index of space use. Hares and rabbits spent time differently among habitats that differ in riskiness. Space use by predators and habitat riskiness affected space use by hares more strongly than space use by rabbits. Residence time of hare was shorter in habitats in which the predator was efficient in searching or capturing prey species. However, hares spent more time in edge habitat when foxes were present, even though foxes are considered ambush predators. Shared predation affected the predator–prey space race for hares positively, and more strongly than the predator–prey space race for rabbits, which were not affected. Shared predation reversed the predator–prey space race between foxes and hares, whereas shared predation possibly also released a negative association and promoted a positive association between our two sympatric prey species. Habitat riskiness, species presence, and prey species’ escape mode and foraging mode (i.e., central‐place vs. noncentral‐place forager) affected the prey space race under shared predation.     

Interspecific variation in chemical defenses in the sea hares (Opisthobranchia: Anaspidea)

Most species of sea hares (Opisthobranchia: Anaspidea) sequester secondary metabolites from their algal diets in their digestive glands. Aplysia Juliana Quoy and Gaimard, 1832, a sea hare that feeds on Ulva spp. and Enteromorpha spp., algae with few or no secondary metabolites, were compared with the sympatric sea hares A. oculifera Adams and Reeve, 1850, A. kurodai (Baba, 1937), and Dolabella auricularia (Solander, 1786), all of which eat chemically rich algae, to see if sequestered secondary metabolites afford protection to sea hares from potential predators. Organic extracts of whole A. Juliana stimulated, and organic extracts of whole D. auricularia deterred feeding by crabs. However, tests with organic extracts of individual body parts indicated that this pattern was due almost exclusively to unpalatability of extracts of D. auricularia digestive glands. Tests with pieces of tissue from the exterior of the animals, or with extracts of such tissues, showed no consistent patterns indicating that A. Juliana were more palatable than other sea hares. Sea hare egg masses do not appear to contain diet-derived secondary metabolites. However, pieces of egg masses of A. Juliana and D. auricularia were universally rejected by crabs and reef fish, and extracts of A. Juliana egg masses deterred feeding by some reef fish. Finally, both opaline secretion of A. Juliana and ink of A. kurodai, but not ink of D. auricularia, none of which appear to contain diet-derived secondary metabolites, deterred feeding by crabs. Opaline secretion from A. Juliana, but not ink from A. kurodai, induced avoidance behavior in crabs. Although sequestered secondary metabolites clearly can affect the palatability of the digestive gland, there is little evidence that they affect the palatibility of the ink, opaline secretion, eggs, or skin, suggesting that sequestered secondary metabolites may not play a key role in anti-predator defense of sea hares.