Light,predation and the lekking behaviour of the ghost swift Hepialus humuli (L.) (Lepidoptera,Hepialidae)

We examined the timing of the crepuscular lekking flight of male ghost swift moths in southern Sweden with respect to variations in: (i) the quality of the visual mating signal; and (ii) the behaviour of potential vertebrate predators (mainly bats). The moths'' display flights started ca. 57 min after sunset, and occurred during 20–30 min at incident light intensities between 10.0 and 2.0 lux. Owing to the falling and more shortwave ambient light after sunset, the brightness contrast between the moth wings and the background (grass) increased steeply at the time of display onset. The silvery white male wing colour thereby seems to maximize conspicuousness, and may be a secondary adaptation that facilitates visibility at low light intensities. The display timing itself is probably determined by other factors, possibly predation. By displaying only for a short period at dusk, the moths seem to avoid most birds, which normally do not forage at these light levels, and gleaning bats, which typically do not start to feed until the light intensity has fallen even further. Nevertheless, aerial-hawking bats were often (54% of the evenings, n = 22) seen at the leks, and one species (Eptesicus nilssonii) frequently fed on the displaying moths (22% of the moths observed, n = 83). H. humuli represents an ancient clade among the Lepidoptera. By restricting its sexual behaviour to a short time window at dusk, when predation risk may be minimized (but still high), it may to some extent compensate for the lack of sophisticated predator defence systems such as aposematic or mimetic coloration, manoeuvrable flight, and ultrasonic hearing, which predominate among the more recent Lepidopteran clades. However, the time window solution restricts the moths'' activities considerably and the lack of defence still carries a considerable cost in terms of predation.     

Increased nest defence of upland‐nesting ducks in response to experimentally reduced risk of nest predation

Parent birds should take greater risks defending nests that have a higher probability of success. Given high rates of mammalian nest predation, therefore, parents should risk more for nests in areas with a lower risk of mammalian predation. We tested this hypothesis using nest defence data from over 1300 nests of six species of dabbling ducks studied in an area where predation risk had been reduced through removal of mammalian predators. When predator removal reduced nest predation, the ducks increased risk taking as predicted. Also as predicted, risk taking varied inversely with body size, an index of annual survival, among species. For ducks to vary nest defence in response to variation in predation risk they must be able to assess the risk of nest predation. Because ducks modified nest defence in the breeding season immediately following predator removal, ducks may be able to assess predator abundance indirectly (e.g. by UV reflection from urine) rather than by seeing or interacting directly with the predators.     

Do predators influence the behaviour of bats?

Many aspects of animal behaviour are affected by real‐time changes in the risk of predation. This conclusion holds for virtually all taxa and ecological systems studied, but does it hold for bats? Bats are poorly represented in the literature on anti‐predator behaviour, which may reflect a lack of nocturnal predators specialized on bats. If bats actually experience a world with minimal anti‐predator concerns, then they will provide a unique contrast within the realm of vertebrate ecology. Alternatively, such predator‐driven behaviour in bats may not yet be fully understood, given the difficulties in working with these highly mobile and nocturnal animals. We provide a wide‐ranging exploration of these issues in bat behaviour. We first cover the basic predator‐prey information available on bats, both on potential predators and the ways in which bats might perceive predators and respond to attacks. We then cover work relevant to key aspects of bat behaviour, such as choice of daytime roosts, the nature of sleep and torpor, evening roost departures, moonlight avoidance, landscape‐related movement patterns, and habitat selection. Overall, the evidence in favour of a strong influence of predators on bat behaviour is equivocal, with the picture clouded by contradictory results and a lack of information on potential predators and the perception of risk by bats. It seems clear that day‐active bats run a considerable risk of being killed by diurnal raptors, which are able to capture bats with relative ease. Thus, bats taking advantage of a pulse of insects just prior to sunset are likely taking risks to gain much‐needed energy. Further, the choice of daytime roosts by bats is probably strongly influenced by roost safety. Few studies, however, have directly addressed either of these topics. As a group, insectivorous temperate‐zone bats show no clear tendency to avoid apparently risky situations, such as activity on moonlit nights. However, some observations are consistent with the idea that predation risk affects choice of movement paths and feeding areas by temperate‐zone bats, as well as the timing of roost departures. The behaviour of tropical bats, on the other hand, seems more generally influenced by predators; this is especially true for tropical nectarivores and frugivores, but also for insectivorous bats. Presumably there are more serious predators on bats in the tropics (e.g. specialized raptors or carnivorous bats), but the identity of these predators is unclear. More information is needed to assess fully the influence of predators on bat behaviour. There is much need for work on the ways in which bats perceive predators via auditory, visual, and olfactory cues, and whether bats have some knowledge of the risks posed by different predators. Also needed is information on how predators attack bats and how bats react to attacking predators. Difficult to obtain, but of critical value, will be information on the nature of the predation risk experienced by bats while away from roosts and during the full darkness of night.     

Morphological anti‐predator defences in the nine‐spined stickleback: constitutive,induced or both?

Environmental differences among populations are expected to lead to local adaptation, while spatial or temporal environmental variation within a population will favour evolution of phenotypic plasticity. As plasticity itself can be under selection, locally adapted populations can vary in levels of plasticity. Nine‐spined stickleback (Pungitius pungitius) originating from isolated ponds (low piscine predation risk, high competition) vs. lake and marine populations (high piscine predation risk, low competition) are known to be morphologically adapted to their respective environments. However, nothing is known about their ability to express phenotypic plasticity in morphology in response to perceived predation risk or food availability/competition. We studied predator‐induced phenotypic plasticity in body shape and armour of marine and pond nine‐spined stickleback in a factorial common garden experiment with two predator treatments (present vs. absent) and two feeding regimes (low vs. high). The predation treatment did not induce any morphological shifts in fish from either habitat or food regime. However, strong habitat‐dependent differences between populations as well as strong sexual dimorphism in both body shape and armour were found. The lack of predator‐induced plasticity in development of the defence traits (viz. body armour and body depth) suggests that morphological anti‐predator traits in nine‐spined stickleback are strictly constitutive, rather than inducible. © 2012 The Linnean Society of London, Biological Journal of the Linnean Society, 2012, ??, ??–??.     

Nesting Success in Crimson Finches: Chance or Choice?

In avian systems, nest predation is one of the most significant influences on reproductive success. Selection for mechanisms and behaviours to minimise predation rates should be favoured. To avoid predation, breeding birds can often deter predators through active nest defence or by modifying behaviours around the nest (e.g. reducing feeding rates and vocalisations). Birds might also benefit from concealing nests or placing them in inaccessible locations. The relative importance of these strategies (behaviour vs. site selection) can be difficult to disentangle and may differ according to life history. Tropical birds are thought to experience higher rates of predation than temperate birds and invest less energy in nest defence. We monitored a population of crimson finches (Neochmia phaeton), in the Australian tropics, over two breeding seasons. We found no relationship between adult nest defence behaviour (towards a model reptile predator) and the likelihood of nest success. However, nest success was strongly related to the visibility of the nest and the structure of the vegetation. We found no evidence that adult nest building decisions were influenced by predation risk; individuals that re‐nested after a predation event did not build their nest in a more concealed location. Therefore, predator avoidance, and hence nest success, appears to be largely due to chance rather than due to the behaviour of the birds or their choice of nesting sites. To escape high predation pressures, multiple nesting attempts both within and between seasons may be necessary to increase reproductive success. Alternatively, birds may be limited in their nest‐site options; that is, high‐quality individuals dominate quality nest sites.     

Predator‐avoidance behaviour in a nocturnal petrel exposed to a novel predator

Many species of bird recognize acoustic and visual cues given by their predators and have complex defence adaptations to reduce predation risk. Recognition of threats posed by specific predators and specialized anti‐predation behaviours are common. In this study we investigated predator recognition and anti‐predation behaviours in a pelagic seabird, Leach's Storm‐petrel Oceanodroma leucorhoa, at a site where predation risk from Great Skuas Stercorarius skua is exceptionally high. Leach's Storm‐petrels breed in burrows and come on land only at night. Counter‐predator adaptations were investigated correlatively in relation to changing natural light levels at night, and experimentally in relation to nocturnal visual and acoustic signals from Great Skuas. Colony attendance by Leach's Storm‐petrels was attuned to changes in light conditions at night and was highest when nights were darkest. This behaviour is likely to reduce predation risk on land; however, specific recognition of Great Skuas and specialized defence behaviours were not found. Leach's Storm‐petrels, in particular apparently non‐breeding individuals, were entirely naïve to the threat posed by Great Skuas and were captured easily in a variety of different ways, on the ground and in the air. Lack of specialized behavioural adaptations in Leach's Storm‐petrels against Great Skuas may be because spatial overlap of breeding distributions of these species appears to be a rare and recent phenomenon.     

Behavioural Response of Bats to Perceived Predation Risk While Foraging

The ability to detect and respond to predation risk while foraging may have important fitness consequences for prey organisms. Anti‐predator behaviours may reduce the probability of mortality because of predation, but they may also be associated with reduced foraging efficiency. Several behaviours of bats have been suggested to serve as anti‐predator responses, and there is evidence that predation, particularly by avian predators such as owls, may be an important cause of bat mortality. Previous studies have attempted to determine whether predator presence affects bat behaviour when emerging from roost sites, but few have examined effects of predator presence on bat behaviour while foraging. In this study, we investigated whether foraging bats respond to predator cues by presenting bats with an acoustic cue simulating the presence of an owl. Within matched trials, which were conducted at different locations each of 18 nights, significantly fewer bat detections were recorded at owl playback stations than at control stations (no auditory cue), suggesting an avoidance response by bats. An acoustic control (i.e. station playing woodpecker calls), however, did not have significantly more detections than the stations playing the owl calls, suggesting that bats may simply be avoiding noise and more detailed investigation is warranted. Although evidence for owl predation on bats is minimal in North America, results of this study may indicate that the perceived presence of owls may represent a factor influencing the behaviour of bats while foraging.     

Predator diversity stabilizes and strengthens trophic control of a keystone grazer

Despite the global vulnerability of predators to extinction, and the critical functional role they play in many ecosystems, there have been few realistic tests of the consequences of predator species deletion (conversely, predator diversity) in natural ecosystems. We performed a four-month field experiment in a southeastern United States salt marsh to test the role of predatory crab diversity in regulating populations of a keystone grazer that can decimate marsh vegetation at high densities. Our results revealed that a combination of this system''s two resident predator species, in comparison to individual species, both stabilize and strengthen predation rates on the potent grazer. Monthly monitoring of predation rates from intense, hot summer months into the cooler autumn indicate this diversity benefit arises from predators responding differentially to changing environmental conditions across seasons. This study provides some of the first experimental field support for the insurance hypothesis from marine ecosystems, suggests that predator temporal complementarity may be more common than currently perceived, and argues for conservation of predator diversity to ensure reliable and effective control of potentially habitat-destroying grazers.     

Nocturnal activity positively correlated with auditory sensitivity in noctuoid moths

We investigated the relationship between predator detection threshold and antipredator behaviour in noctuoid moths. Moths with ears sensitive to the echolocation calls of insectivorous bats use avoidance manoeuvres in flight to evade these predators. Earless moths generally fly less than eared species as a primary defence against predation by bats. For eared moths, however, there is interspecific variation in auditory sensitivity. At the species level, and when controlling for shared evolutionary history, nocturnal flight time and auditory sensitivity were positively correlated in moths, a relationship that most likely reflects selection pressure from aerial-hawking bats. We suggest that species-specific differences in the detection of predator cues are important but often overlooked factors in the evolution and maintenance of antipredator behaviour.     

Predation-risk effects of predator identity on the foraging behaviors of frugivorous bats

Predators directly and indirectly affect the density and the behavior of prey. These effects may potentially cascade down to lower trophic levels. In this study, we tested the effects of predator calls (playbacks of bird vocalizations: Tyto alba, Speotyto cunicularia, and Vanellus chilensis), predator visual stimuli (stuffed birds) and interactions of visual and auditory cues, on the behavior of frugivore phyllostomid bats in the field. In addition, we tested if the effects of predation risk cascade down to other trophic levels by measuring rates of seed dispersal of the tree Muntingia calabura. Using video recording, we found that bats significantly decreased the foraging frequency on trees when a visual cue of T. alba was present. However, no stimuli of potential predatory birds, including vocalization of T. alba, affected bat foraging frequency. There was a change in bat behavior during 7 min, but then their frequency of activity gradually increased. Consequently, the presence of T. alba decreased by up to ten times the rate of seed removal. These results indicate that risk sensitivity of frugivorous phyllostomid bats depends on predator identity and presence. Among the predators used in this study, only T. alba is an effective bat predator in the Neotropics. Sound stimuli of T. alba seem not to be a cue of predation risk, possibly because their vocalizations are used only for intraspecific communication. This study emphasizes the importance of evaluating different predator stimuli on the behavior of vertebrates, as well as the effects of these stimuli on trait-mediated trophic cascades.     

Spatial Partitioning of Predation Risk in a Multiple Predator-Multiple Prey System

ABSTRACT Minimizing risk of predation from multiple predators can be difficult, particularly when the risk effects of one predator species may influence vulnerability to a second predator species. We decomposed spatial risk of predation in a 2-predator, 2-prey system into relative risk of encounter and, given an encounter, conditional relative risk of being killed. Then, we generated spatially explicit functions of total risk of predation for each prey species (elk [Cervus elaphus] and mule deer [Odocoileus hemionus]) by combining risks of encounter and kill. For both mule deer and elk, topographic and vegetation type effects, along with resource selection by their primary predator (cougars [Puma concolor] and wolves [Canis lupus], respectively), strongly influenced risk of encounter. Following an encounter, topographic and vegetation type effects altered the risk of predation for both ungulates. For mule deer, risk of direct predation was largely a function of cougar resource selection. However, for elk, risk of direct predation was not only a function of wolf occurrence, but also of habitat attributes that increased elk vulnerability to predation following an encounter. Our analysis of stage-based (i.e., encounter and kill) predation indicates that the risk effect of elk shifting to structurally complex habitat may ameliorate risk of direct predation by wolves but exacerbate risk of direct predation by cougars. Information on spatiotemporal patterns of predation will be become increasingly important as state agencies in the western United States face pressure to integrate predator and prey management.     

Threat‐sensitive predator avoidance by pike larvae

The threat‐sensitive predator avoidance (TSPA) hypothesis was tested on hatchery‐reared pike Esox lucius larvae. Larval swimming activity, food attacks upon zooplankton, escapes, immobility behaviour, vigilance, as well as time in vegetation under different predation risk were measured. Single larvae were video‐filmed in aquaria allowing them to have visual contact with a small or a large perch Perca fluviatilis as predator. The odds of fleeing increased significantly if the larvae were exposed to a large predator instead of a small one. Swimming activity and foraging decreased significantly in the presence of a predator compared to the control. On the other hand, no significant effect was detected in time spent in the vegetation, and in vigilance of larvae, measured as time intervals between food attacks. The findings suggest that pike larvae primarily flee in the presence of a large predator, whereas they remain immobile, and forage, when possible, in the presence of a small predator. Sometimes a lack of response between the large and the small predator treatments was detected, which suggests that the antipredator response has a threshold, and when increasing the threat, the prey response does not increase. In the present paper it is demonstrated that hatchery‐reared pike larvae respond to the level of threat, and thereby seem to be risk adjusting as predicted.     

Behaviors of Western Spruce Budworm Moths (Choristoneura occidentalis) as Defences Against Bat Predation

We investigated potential defense behaviors of adult western spruce budworm (Choristoneura occidentalis), a non-auditive lepidopteran, against bat predation. Although western spruce budworm moths started to fly before sunset, earlier than many species of moths, temporal isolation of flying moths from foraging bats was incomplete as moths were most active after sunset once bats were foraging. Flying C. occidentalis were most active close to their host trees, and thus were isolated from some bat activity because vegetation limits foraging by some bats. Moths mostly flew near the tops of trees, an area that may have a high predation pressure from bats. Resting western spruce budworm spent little time fluttering their wings or crawling, behaviors that are used as cues by gleaning bats. The outbreak nature of this species, in which large numbers of moths are active at one time, may allow dilution effects to reduce predation risk.     

Habitat deterioration and efficiency of antipredator strategy in a meadow-breeding wader,Temminck's stint (Calidris temminckii)

Many populations of waders breeding on open shores and shores with short vegetation especially on the Baltic coasts have recently become endangered. The declines have taken place simultaneously with human-induced loss and deterioration of habitats due to eutrophication and overgrowth. To investigate mechanisms by which habitat changes could affect breeding success and ultimately population dynamics, we studied an endangered coastal population of Temminck's stint. We hypothesized that the rate of nest predation has become higher because the nest defence strategy (early detection of predator and early departure from the nest), which originally evolved in open habitats, is less effective on shores with reduced visibility. As predicted, nests survived better on wide than on narrow shores. Predation made a major contribution to this trend, although successful and predated nests did not differ in concealment at a microhabitat scale. The better the visibility from the nest, the longer was the flushing distance, but only in response to alarm calls or behaviour of other species, not when they were absent. Temminck's stints seem to obtain information about an approaching predator visually from sentinels. Therefore, it is essential that there is at least moderate visibility around the nest. We conclude that habitat characteristics – visibility from the nest and sentinel birds – affect the effectiveness of the nest defence strategy of Temminck's stint. These should be taken into account when seeking causes and mechanisms for declines of Temminck's stint and other waders of open and shortly vegetated shores. Received: 5 January 1998 / Accepted: 20 April 1998     

Non‐pathogenic aquatic bacteria activate the immune system and increase predation risk in damselfly larvae

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Constrained plasticity in switching across life stages: pre- and post-switch predators elicit early hatching

The timing of many life history events shows phenotypic plasticity in response to the risk of predation. Theory predicts that increased risk of mortality in an early stage should select for switching earlier, while a higher risk after the transition should select for switching later. Here we examined the effects of stage-specific predation risk on the timing of hatching of Rana temporaria. Embryos were exposed to chemical cues from either an egg predator (Haemopis sanguisuda) or a tadpole predator (Aeshna cyanea) to evaluate three specific hypotheses: (1) a fixed intermediate response, (2) a ‘fixed predator’ response (i.e., either anticipation or delay), and (3) a specific predator response (both anticipation and delay). Rana temporaria embryos did not discern between pre- and post-hatching specific predators, and they hatched prematurely regardless predator type. These results suggest that R. temporaria embryos respond to predation risk in a fixed way by hatching early, and that they use cues stemming from injured conspecifics, which provides a simple, conservative mechanism of risk assessment. In conclusion, our data are not anticipated by the theoretical consideration that organisms should spend less time in more dangerous environments, but they confirm an invariable adjustment of hatching time in response to an inscrutable predation risk (response to a fixed-predator) in connection with a consistent mechanism mediating the perception of predation risk.     

Diverse strategies that animals use to deter intraspecific predation

Intraspecific predation is a special case of prey–predator system that is taxonomically widespread. While a heterospecific predator's main goal is to achieve nutrition, intraspecific predation provides conspecifics with other benefits including elimination of competitors for resources and mates. Traditionally intraspecific predation is termed based on the context they occur within, for example egg cannibalism, infanticide and sexual cannibalism. These diverse forms of intraspecific predation and the strategies by which animals are known to deter them are summarized categorically in this review. The diversity of defence strategies animals deploy against conspecific predators is appreciable and raises interesting questions on their evolution for future research.     

Strategic Escape Direction: Orientation,Turning, and Escape Trajectories of Zebra‐Tailed Lizards (Callisaurus draconoides)

A prey's body orientation relative to a predator's approach path may affect risk of fleeing straight ahead. Consequently, prey often turn before fleeing. Relationships among orientation, turn, and escape angles and between these angles and predation risk have not been studied in terrestrial vertebrates and have rarely been studied in the field. Escape angles are expected to lead away from predators and be highly variable to avoid being predictable by predators. Using approach speed as a risk factor, we studied these issues in the zebra‐tailed lizard, Callisaurus draconoides. Lizards fled away from human simulated predators, but most did not flee straight away. Escape angles were variable, as expected under the unpredictability hypothesis, and had modes at nearly straight away (i.e., 0°) and nearly perpendicular to the predator's approach path (90°). The straight away mode suggests maximal distancing from the predator; the other mode suggests maintaining ability to monitor the predator or possibly an influence of habitat features such as obstacles and refuges that differ among directions. Turn angles were larger when orientation was more toward the predator, and escape angles were closer to straight away when turn angles were larger. Turning serves to reach a favorable fleeing direction. When orientation angle was more toward the predator, escape angle was unaffected, suggesting that turn angle compensates completely for increased risk of orientation toward the predator. When approached more rapidly, lizards fled more nearly straight away, as expected under greater predation risk. Turn angles were unrelated to approach speed.     

Camera trap data suggest uneven predation risk across vegetation types in a mixed farmland landscape

Ground‐nesting farmland birds such as the grey partridge (Perdix perdix) have been rapidly declining due to a combination of habitat loss, food shortage, and predation. Predator activity is the least understood factor, especially its modulation by landscape composition and complexity. An important question is whether agri‐environment schemes such as flower strips are potentially useful for reducing predation risk, for example, from red fox (Vulpes vulpes). We employed 120 camera traps for two summers in an agricultural landscape in Central Germany to record predator activity (i.e., the number of predator captures) as a proxy for predation risk and used generalized linear mixed models (GLMMs) to investigate how the surrounding landscape affects predator activity in different vegetation types (flower strips, hedges, field margins, winter cereal, and rapeseed fields). Additionally, we used 48 cameras to study the distribution of predator captures within flower strips. Vegetation type was the most important factor determining the number of predator captures and capture rates in flower strips were lower than in hedges or field margins. Red fox capture rates were the highest of all predators in every vegetation type, confirming their importance as a predator for ground‐nesting birds. The number of fox captures increased with woodland area and decreased with structural richness and distance to settlements. In flower strips, capture rates in the center were approximately 9 times lower than at the edge. We conclude that the optimal landscape for ground‐nesting farmland birds seems to be open farmland with broad extensive vegetation elements and a high structural richness. Broad flower blocks provide valuable, comparatively safe nesting habitats, and the predation risk can further be minimized by placing them away from woods and settlements. Our results suggest that adequate landscape management may reduce predation pressure.     

Trading off safety against food: state dependent habitat choice and foraging in crucian carp

The influence of hunger level and predation risk on habitat choice and foraging in crucian carp, Carassius carassius, were studied in a laboratory experiment. Experiments were carried out in aquaria with or without a predator (pike, Esox lucius). Habitat use and foraging activity of three-fish foraging groups of either fed or hungry crucian carp were studied. Fish were allowed to choose between an open (risky) habitat with Tubifex worms and a habitat with dense vegetation (safe) without food. Habitat use was significantly affected by both risk of predation and hunger level. Crucian carp spent less time in the open habitat when there was a predator present and they also spent less time there when fed than when hungry. Furthermore, there was a significant interaction between risk of predation and hunger level, indicating a state-dependent trade-off between food acquisition and predator avoidance.