Predation Danger Research Articles

Do sex and habitat differences in antipredator behavior of Western Sandpipers Calidris mauri reflect cumulative or compensatory processes?

Individuals manage their risk of predation in different ways in different situations. We studied the use of anti-predator behavior by Western Sandpipers (Calidris mauri) at Bahia Santa Maria, northwestern Mexico, foraging in three habitats that differed in presumed predation danger. Brackish flats are completely open, making them theoretically less dangerous for feeding sandpipers than mangroves and cattail marshes, which have closer visual horizons. Western Sandpipers are sexually dimorphic, with females about 15% longer-billed and 10% heavier than males. We previously showed that male and female sandpipers differed in their habitat choice and relative body mass in ways consistent with differential responses to predation danger (Fernandez and Lank in Condor 108:547–557, 2006). Contrary to expectations, however, females were overrepresented in more dangerous habitats. Here, we examine differential usage across habitats and between the sexes of three anti-predator tactics—flock size, density within flocks, and vigilance rate—that may be used cumulatively to reinforce safety, or as trade-offs that compensate for levels of usage of each. We hypothesized, and found, that ordered differences occur among habitats, and that controlling for other factors, females were more cautious than males. For the most part, the use of these three tactics appeared to be cumulative, rather than compensatory. However, with respect to habitat use, birds appeared to compensate for the higher probability of mortality intrinsic to the use of higher-danger habitats by increasing the use of vigilance, foraging in tighter flocks, and maintaining lighter body weights (females only). Thus, both cumulative and compensatory processes operate among anti-predator tactics to determine the net level of safety and trade-off against other factors.

Prioritized phenotypic responses to combined predators in a marine snail

Although many species face numerous predators in nature, the combined impact of multiple predators on the inducible defenses of prey has rarely been studied. Prey may respond with an intermediate phenotype that balances the risk from several sources or may simply respond to the most dangerous predator. I examined the separate and combined effects of the presence of shell-breaking (crabs, Cancer productus) and shell-entry (seastars, Pisaster ochraceus) predators fed conspecific snails on the defensive shell morphology and antipredator behavior of a marine snail (Nucella lamellosa). When exposed to each feeding predator separately, snails responded with a combination of morphological defenses that reflect the attack mode of the predator and a generalized behavioral response. Snails responded to feeding crabs by increasing refuge use and producing a thick, rotund shell. Snails responded to feeding seastars with increased refuge use but produced elongate shells with high spires that allowed for greater retraction of the soft tissue. Seastar-induced phenotypes reduced susceptibility to seastars relative to crab-induced phenotypes, but crab-induced phenotypes did not significantly reduce susceptibility to crabs, indicating an asymmetrical functional trade-off. When feeding predators were combined, snails produced a morphological phenotype similar to that expressed in the presence of the predator that imposed the highest mortality at the population level, suggesting that predator-induced morphology was prioritized according to predation risk. These results suggest that prioritizing conflicting defenses according to predator danger may be a common strategy for prey responding to combined predators, particularly in conjunction with generalized behavioral responses that reduce overall risk in multiple-predator environments.

Oriented responses of grapevine moth larvae Lobesia botrana to volatiles from host plants and an artificial diet on a locomotion compensator

Larvae of the grapevine moth Lobesia botrana (Lepidoptera: Tortricidae) are a major pest of vine, Vitis vinifera. As larvae have limited energy reserves and are in danger of desiccation and predation an efficient response to plant volatiles that would guide them to food and shelter could be expected. The responses of starved 2nd or 3rd instar larvae to volatile emissions from their artificial diet and to single host plant volatiles were recorded on a locomotion compensator. Test products were added to an air stream passing over the 30 cm diameter servosphere. The larvae showed non-directed walks of low rectitude in the air stream alone but changed to goal-oriented upwind displacement characterised by relatively straight tracks when the odour of the artificial diet and vapours of methyl salicylate, 1-hexanol, ( Z)-3-hexen-1-ol, terpinen-4-ol, 1-octen-3-ol, ( E)-4,8-dimethyl-1,3,7-nonatriene and ( Z)-3-hexenyl acetate were added to the air stream. This chemoanemotactic targeted displacement illustrates appetence for certain volatile cues from food by starved Lobesia larvae. Analysis of the larval behaviour indicates dose dependent responses to some of the host plant volatiles tested with a response to methyl salicylate already visible at 1 ng, the lowest source dose tested. These behavioural responses show that Lobesia larvae can efficiently locate mixtures of volatile products released by food sources as well as single volatile constituents of their host plants. Such goal-oriented responses with shorter travel time and reduced energy loss are probably of importance for larval survival as it decreases the time they are exposed to biotic and abiotic hazards.

Danger on the rise: diurnal tidal state mediates an exchange of food for safety by the bar-bellied sea snake Hydrophis elegans

Prey vulnerability to predation can depend on abiotic conditions. Thus, prey individuals may adjust their investment in anti-predator defense according to changes in one or more abiotic fac- tors. We explored this possibility in Shark Bay, Western Australia, where the bar-bellied sea snake Hydrophis elegans is under threat of predation by the tiger shark Galeocerdo cuvier, asking specifi- cally whether the diurnal tidal state influenced snakes' selection of exposed foraging habitat (sand flat) and refuge habitat (seagrass). At high tide, when both habitats were easily accessible to sharks, H. elegans selected seagrass habitats, where its food is relatively scarce. At low tide, when sharks had limited access to both habitats, H. elegans used the 2 habitats equally but foraged exclusively over sand flats. We concluded that H. elegans is sensitive to the danger of tiger shark predation and trades food for the safety of a refuge when diurnal tidal conditions in its foraging habitat expose it to sharks. Our results suggest that predation risk should be considered in studies of sea snake habitat use and that important variation in predator-prey interactions may be missed if relevant abiotic conditions are ignored.

Evidence against maximization of gross rate of seed delivery to the burrow in food-hoarding eastern chipmunks, Tamias striatus

The central place foraging model predicts the optimal load sizes of prey carried back to a central place. When the rate of prey loading at the patch declines with time spent in the patch, the optimal, rate-maximizing load sizes increase with round-trip travel times between patch and central place. Numerous tests of this rate-maximizing currency have been carried out with eastern chipmunks carrying loads of seeds to their burrow. All tests have provided consistent qualitative support for the model (load sizes increase with distance) as well as consistent quantitative rejection of the model (loads carried are always considerably smaller than optimal). Confidence in the repeated rejections of the currency is weak because the predicted optimal load sizes stem from extrapolations of the loading function beyond the data used to estimate it. In this study, we provided subjects in the field with a food patch that provided the same increasing interval schedule of prey arrival at 2 m and 15 m from their burrow. Results confirm the quantitative failure of the rate-maximizing currency for the central place foraging model. We propose that the consistent failures of rate maximization with chipmunks are probably due to the higher predation danger when collecting seed from a patch compared to travelling.

Can you dig it? Use of excavation, a risky foraging tactic, by dugongs is sensitive to predation danger

Foraging and vigilance are mutually exclusive for some foraging tactics but not others. Thus, in response to changes in predation danger, prey species with multiple foraging tactics may switch facultatively between them, allowing for differential levels of vigilance. Using data from focal observations collected over 4 years (2002–2004, 2006) in Shark Bay, Western Australia, we explored the use of two tactics, cropping and excavation, by dugongs, Dugong dugon, foraging under risk of predation by tiger sharks, Galeocerdo cuvier. Overall, dugongs predominantly used the cropping tactic, which allows for regular visual scans, to harvest temperate sea grass species. Dugongs only used the excavation tactic, which precludes regular visual scans but allows individuals to access the nutritious rhizomes of preferred tropical sea grass species, in months when tropical species were most available (February–May). However, during these months the time dugongs allocated to excavation was inversely related to shark abundance rather than the availability of these sea grass species. We conclude that use of foraging tactics by dugongs is sensitive to predation danger, and that individuals manage their risk of mortality via reduced use of a profitable but potentially hazardous tactic when the likelihood of encountering predators is high. Excavating dugongs are more likely to disrupt sea grass meadow structure and promote succession than are those engaged in cropping. Thus, by altering the time dugongs devote to these alternative tactics, tiger sharks may exert an indirect effect on sea grass patch composition and structure and, ultimately, benthic communities.

Can redistribution of breeding colonies on a landscape mitigate changing predation danger?

The reproductive success of colonially breeding species depends in part upon a trade‐off between the benefit of a dilution effect against nestling predation within larger colonies and colony conspicuousness. However, there may be no net survivorship benefit of dilution if smaller colonies are sufficiently inconspicuous. This raises the question about how the size distribution of breeding colonies on a landscape might change as the predation danger for nestlings changes. In southwest British Columbia, Canada, bald eagle Haliaeetus leucocephalus populations have increased exponentially at ∼5% per year in recent decades and prey upon nestlings of colonial breeding great blue herons Ardea herodias faninni. Motivated by field data on reproductive success in relation to colony size, modeling is used to ask under which circumstances trading off a dilution benefit against colony conspicuousness can improve population reproductive success. That is, which colonial nesting distribution, dispersed and cryptic versus clumped and conspicuous, best mitigates predation danger on nestlings? When predators are territorial, the modeling predicts a dispersed nesting strategy as attack rate increases, but not as predator numbers increase. When predators are non‐territorial, the modeling predicts a dispersed nesting strategy as predator numbers and/or attack rates increase. When predators are both territorial and non‐territorial, colonial nesting within a predator's territory improves reproductive success when attack rates are low. This suggests nesting in association with territorial predators may offer decreased levels of predation when compared with nesting amongst non‐territorial predators. Thus a change in the colony size distribution of colonially breeding species might be anticipated on a landscape experiencing a change in predation danger.

Can redistribution of breeding colonies on a landscape mitigate changing predation danger?

Can redistribution of breeding colonies on a landscape mitigate changing predation danger?

Fear factor: do dugongs (Dugong dugon) trade food for safety from tiger sharks (Galeocerdo cuvier)?

Predators can influence plants indirectly by altering spatial patterns of herbivory, so studies assessing the relationship between perceived predation risk and habitat use by herbivores may improve our understanding of community organization. In marine systems, the effects of predation danger on space use by large herbivores have received little attention, despite the possibility that predator-mediated alterations in patterns of grazing by these animals influence benthic community structure. We evaluated the relationship between habitat use by foraging dugongs (Dugong dugon) and the threat of tiger shark predation in an Australian embayment (Shark Bay) between 1997 and 2004. Dugong densities were quantified in shallow (putatively dangerous) and deep (putatively safe) habitats (seven survey zones allocated to each habitat), and predation hazard was indexed using catch rates of tiger sharks (Galeocerdo cuvier); seagrass volume provided a measure of food biomass within each zone. Overall, dugongs selected shallow habitats, where their food is concentrated. Foragers used shallow and deep habitats in proportion to food availability (input matching) when large tiger sharks were scarce and overused deep habitats when sharks were common. Furthermore, strong synchrony existed between daily measures of shark abundance and the extent to which deep habitats were overused. Thus, dugongs appear to adaptively manage their risk of death by allocating time to safe but impoverished foraging patches in proportion to the likelihood of encountering predators in profitable but more dangerous areas. This apparent food-safety trade-off has important implications for seagrass community structure in Shark Bay, as it may result in marked temporal variability in grazing pressure.

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

Prey species must adapt their behavior to avoid predation. As a key prey item for lions (Panthera leo), plains zebras (Equus burchelli) were expected to respond to immediate threats posed by lions in their area. In addition, zebras were predicted to exhibit behavior tuned to reduce the potential for encounters with lions, by modifying their movement patterns in the times of day and habitats of greatest lion danger. We studied a population of approximately 600 plains zebra living in Ol Pejeta Conservancy, Kenya. We found that zebra abundance on or near a grassland patch was lower if lions had also been observed on that patch during the same day. Predation danger was highest in grassland habitat during the night, when lions were more active. Zebra sightings and global positioning system radio collar data indicated that zebras also reduced their use of grassland at night, instead using more woodland habitat. Zebras moved faster and took sharper turns in grassland at night. It is hypothesized that these more erratic movements assist zebras in avoiding detection or capture by lions.

Living on the edge: dugongs prefer to forage in microhabitats that allow escape from rather than avoidance of predators

When threatened with predation, foraging prey can cease feeding and seek refuge or shift to feeding sites (microhabitats) offering increased safety. Predator-induced microhabitat shifts by large herbivores are of interest to ecologists because spatial patterns of foraging by these animals shape plant communities. The influence of predation risk on microhabitat use by large herbivores in marine systems remains poorly understood. We explored the relationship between microhabitat use by dugongs, Dugong dugon, and tiger shark, Galeocerdo cuvier, predation risk in an Australian embayment over 3 years. Use by foraging dugongs of two seagrass microhabitats, edge (lower-quality seagrass, swift escape from sharks) and interior (higher-quality seagrass, fewer escape options), was monitored in seven survey zones. We indexed predation danger using catch rates of tiger sharks that were greater than 3.0 m in total length. The degree of dissimilarity between forager densities in edge and interior microhabitats was a function of tiger shark abundance: foragers underused edge (safe) microhabitat when sharks were scarce, overused it when sharks were common, and responded to daily changes in shark abundance in a threat-sensitive fashion, showing the greatest preference for edges when shark abundance was highest. We conclude that dugongs manage their probability of death by allocating more time to safe but lower-quality feeding microhabitats when the likelihood of encountering sharks is elevated. Dugong grazing can influence seagrass biomass and patch composition, so tiger sharks probably affect the microhabitat structure of seagrass meadows, and ultimately their benthic communities, indirectly by altering the way that dugongs use feeding patches.

Diurnal and Nocturnal Roost Site Fidelity of Dunlin (Calidris Alpina Pacifica) at Humboldt Bay, California

AbstractShorebird roosts are often considered traditional, on the basis of predictable occupancy by large numbers of birds over long periods. However, fidelity of individuals to roosts at fine spatial and temporal scales, particularly at night, has rarely been described. We compared diurnal and nocturnal use of high-tide roosts by radiotagged Dunlin (Calidris alpina pacifica) wintering (November-March) at Humboldt Bay, California. Despite high fidelity to the study area, fidelity to particular roosts was relatively low and highly variable. At night, Dunlin used fewer roosts, were more faithful to primary roosts, and moved shorter distances between successive roosts than during the day. Day and night roosts differed in location, habitat, and distance from tidal flats. At night, Dunlin made greater use of pasture, and less use of islands and manmade structures. Day and night strategies of high-tide space use by Dunlin may be related to differences in food availability or predation danger. Our results illustrate that notions of tradition and site fidelity are scale-dependent and that knowledge of space use across the full range of environmental conditions is necessary for appropriate management of shorebird habitat.Fidelidad a los Sitios de Descanso Diurnos y Nocturnos en Calidris alpina pacifica en la Bahía de Humboldt, California

Relationship Between Stopover Site Choice of Migrating Sandpipers, Their Population Status, and Environmental Stressors

Measures of animal behavior can be used in a variety of situations to make inferences about the environment and population status. Work by our research group shows that migratory shorebirds adjust their usage of, and behavior at, stopover sites in response to environmental conditions. Motivated by this, we built an individual-based model of migrating shorebirds moving through a sequence of alternating small and large stopover sites. birds at larger sites are safer from predators, but we assumed that less food is available than at small sites. In the model, both predation risk and food intake are densitydependent, and the behavior of migrants is controlled by two rules: one that determines whether a bird will depart a stopover site, and one that controls the individual’s foraging versus vigilance intensity. The optimal behavior is calculated by maximizing a payoff function that depends on arrival date and arrival energy stores at the final site. We used this model to predict mass gain, foraging intensity, and usage by migrants of small and large sites under various conditions. We examined the effects of a flyway-wide reduction in the amount of food, a flyway-wide increase in predation danger, and the effects of lowering the overall population size. The mass action of many individuals, each optimizing its migration timing and routing, leads to the emergence of distinctive patterns of behavior and site choice under these differing environmental conditions. When food availability is reduced throughout the flyway, our model predicts that foraging intensity increases at every stopover site, thereby forcing birds to accept greater danger to maintain the fitness benefit of a timely arrival to the breeding area. A flyway-wide increase in predation danger results in fewer migrants choosing (and/or migrants staying a shorter time at) small stopover sites, balanced by a higher usage of large sites. These effects contrast with what is observed under true population declines, when the usage of both small and large sites declines.

DIURNAL AND NOCTURNAL ROOST SITE FIDELITY OF DUNLIN (CALIDRIS ALPINA PACIFICA) AT HUMBOLDT BAY, CALIFORNIA

Abstract Shorebird roosts are often considered traditional, on the basis of predictable occupancy by large numbers of birds over long periods. However, fidelity of individuals to roosts at fine spatial and temporal scales, particularly at night, has rarely been described. We compared diurnal and nocturnal use of high-tide roosts by radiotagged Dunlin (Calidris alpina pacifica) wintering (November-March) at Humboldt Bay, California. Despite high fidelity to the study area, fidelity to particular roosts was relatively low and highly variable. At night, Dunlin used fewer roosts, were more faithful to primary roosts, and moved shorter distances between successive roosts than during the day. Day and night roosts differed in location, habitat, and distance from tidal flats. At night, Dunlin made greater use of pasture, and less use of islands and manmade structures. Day and night strategies of high-tide space use by Dunlin may be related to differences in food availability or predation danger. Our results illus...

Tufted Puffins (Fratercula Cirrhata) Respond to Predation Danger During Colony Approach Flights

AbstractIn spite of their putative importance in the evolution of certain traits (e.g., nocturnality, coloniality, cliff nesting), the effects of aerial predators on behavior of adult seabirds at colonies have been poorly investigated. We hypothesized that Tufted Puffins (Fratercula cirrhata) respond to danger posed by aerial predators by modifying their behavior to mitigate danger. We observed Tufted Puffins making repeated colony fly-ins and departures and characterized (1) the timing of this behavior, (2) the activity rate (number of birds arriving or departing), and (3) the risk-level of activity, with respect to predation danger posed by Bald Eagles (Haliaeetus leucocephalus) and Peregrine Falcons (Falco peregrinus). As we predicted, we found that Tufted Puffins (1) dilute danger by synchronizing their fly-in and departure activities, (2) reduce fly-in and departure activity rates when predators are present, and (3) switch to lower-risk fly-in activities (e.g., staying over water where they have an escape route from an aerial attack) when predators are present.Réaction de Fratercula cirrhata au Danger de Prédation au cours des Vols d'Approche de la Colonie

TUFTED PUFFINS (FRATERCULA CIRRHATA) RESPOND TO PREDATION DANGER DURING COLONY APPROACH FLIGHTS

Abstract In spite of their putative importance in the evolution of certain traits (e.g., nocturnality, coloniality, cliff nesting), the effects of aerial predators on behavior of adult seabirds at colonies have been poorly investigated. We hypothesized that Tufted Puffins (Fratercula cirrhata) respond to danger posed by aerial predators by modifying their behavior to mitigate danger. We observed Tufted Puffins making repeated colony fly-ins and departures and characterized (1) the timing of this behavior, (2) the activity rate (number of birds arriving or departing), and (3) the risk-level of activity, with respect to predation danger posed by Bald Eagles (Haliaeetus leucocephalus) and Peregrine Falcons (Falco peregrinus). As we predicted, we found that Tufted Puffins (1) dilute danger by synchronizing their fly-in and departure activities, (2) reduce fly-in and departure activity rates when predators are present, and (3) switch to lower-risk fly-in activities (e.g., staying over water where they have an ...

Sex, Age, and Body Size Distributions of Western Sandpipers During the Nonbreeding Season With Respect to Local Habitat

AbstractWe documented the local density and sex, age-class, and body size distributions of Western Sandpipers (Calidris mauri) among habitats at Bahía Santa María, northwestern Mexico, during the nonbreeding season. Three habitats were recognized: brackish flats, mangroves, and cattail marshes, which we ranked as richest to poorest in food resources and safest to most dangerous in predation danger. Western Sandpiper population structure differed among habitats. Bird densities were highest in brackish flats, the richest and safest habitat, and males and adults of both sexes were overrepresented. In cattail marshes, which appeared to be the poorest and most dangerous habitat, bird densities were lower, and the sex ratio and age ratios within each sex were more even. In mangroves, bird densities were similar to those in cattail marshes, but sex and age ratios were similar to those in brackish flats. Exposed culmen, an index of structural size, was not related to habitat use in either sex. Body mass of immature males was more variable than that of adults among habitats and immature males gained mass throughout the winter. Birds in brackish flats and mangroves were initially heavier, but tended to lose mass, whereas birds in cattail marshes were initially lighter, but tended to gain mass. Mass distributions thus converged in late winter. While the social and ecological causes and significance of differential sex and age-class distributions among habitats remain largely unquantified, evidence from this and previous studies suggests that nonbreeding population structure is a common phenomenon with important implications for migratory shorebirds.

Physiological responses of topmouth gudgeon, Pseudorasbora parva, to predator cues and variation of current velocity

Predators, either through direct or indirect encounter and current velocity, are frequently stressful to fish living in stream waters. In nature, fish may experience both current velocity stress and predation danger simultaneously. Experiments were carried out to clarify to what extent predation risk (with reference to different types of predatory cues) and current velocity can induce physiological stress in a running-water dwelling fish, topmouth gudgeon (Pseudorasbora parva). Fish were exposed to an alarm substance, predator odor, and visual cue, as well to combinations of predation risk and elevated current velocities. Metabolic rate, ventilation rate and fish activity were measured. Results showed that irrespective of the type of encounter, the presence of predator imposed physiological stress on fish. Metabolic rate were 0.983 ± 0.312, 0.641 ± 0.151, 0.572 ± 0.063, and 0.277 ± 0.016 mg O2 W−1 h−1 following presence of alarm substance, visual cue, predator odor and control, respectively. Dramatic changes in ventilation rate and activity affirmed that alarm substance induced the strongest stress, followed by predator odor and visual cue. Reactions appeared to mirror the extent of fish perceiving danger of predation. Predation risk together with current velocity induces stronger stress, much stronger than if the current velocity works as a single stressor. However, the interaction between predation risk and current velocity did not have a significant effect on metabolic function; magnitude of metabolic response to high current velocity might mask the metabolic response to predator presence. Small fish living in stream habitats that face local predation risk would spend higher energy expenditure that may have negative impacts on growth, and hence their fitness.

Tradeoffs between food abundance and predation danger in spatial usage of a stopover site by western sandpipers,Calidris mauri

Foragers use a variety of anti‐predator behaviours to increase their safety from predators. While foraging, animals should alter usage within or between sites to balance the benefits of feeding with the costs of predation. I tested how the distribution of food abundance and predation danger interacts to explain spatial usage (i.e. distance from shore) by migratory western sandpipers (Calidris mauri) at Boundary Bay, British Columbia, Canada, during northward and southward migrations. At Boundary Bay there are opposing spatial gradients in the distribution of food abundance and safety from predators. Predation danger for sandpipers is high near the shoreline where there is approach cover for falcons and decreases with distance from shore. Food abundance for sandpipers declines as distance from the shoreline increases. Food and danger attributes at Boundary Bay also differ temporally, such that food abundance is higher during southward migration, and predation danger is higher during northward migration. The spatial usage by western sandpipers balances the tradeoff between the opposing spatial gradients in food and safety. For both migratory periods spatial usage of the mudflat by sandpipers is highest at distances from the shoreline where food abundance and predation danger are intermediate. During the northward migration sandpiper usage is highest between 150 and 500 m from the shoreline, and during the southward migration sandpiper usage is highest between 100 and 600 m from the shoreline. Despite temporal differences in food and danger attributes, spatial usage of the site by sandpipers does not differ between migratory periods. Understanding how the distribution of food abundance and predation danger interact to affect the within site usage by shorebirds has important implications for assessments of site quality.

SEX, AGE, AND BODY SIZE DISTRIBUTIONS OF WESTERN SANDPIPERS DURING THE NONBREEDING SEASON WITH RESPECT TO LOCAL HABITAT

Abstract We documented the local density and sex, age-class, and body size distributions of Western Sandpipers (Calidris mauri) among habitats at Bahia Santa Maria, northwestern Mexico, during the nonbreeding season. Three habitats were recognized: brackish flats, mangroves, and cattail marshes, which we ranked as richest to poorest in food resources and safest to most dangerous in predation danger. Western Sandpiper population structure differed among habitats. Bird densities were highest in brackish flats, the richest and safest habitat, and males and adults of both sexes were overrepresented. In cattail marshes, which appeared to be the poorest and most dangerous habitat, bird densities were lower, and the sex ratio and age ratios within each sex were more even. In mangroves, bird densities were similar to those in cattail marshes, but sex and age ratios were similar to those in brackish flats. Exposed culmen, an index of structural size, was not related to habitat use in either sex. Body mass of immat...