Effects of risk, cost, and their interaction on optimal escape by nonrefuging Bonaire whiptail lizards, Cnemidophorus murinus

Optimal escape theory seeks to explain variation in the distanceto an approaching predator at which the prey initiates escape(flight initiation distance). Flight initiation distance increaseswhen predators pose a greater threat and decreases when escapecosts increase. Although optimal escape theory has been highlysuccessful, its predictions have been tested primarily for speciesthat escape to discrete refuges, and most studies have focusedon single risk or cost factors. We present data from two experimentsin which two risks or a risk and a cost varied in Bonaire whiptaillizards (Cnemidophorus murinus) that escaped without enteringrefuges. Our data verify several predictions about optimal escapefor nonrefuging lizard prey. Two risk factors, speed and directnessof approach by the predator, interacted. Directly approachedlizards had greater flight initiation distances than did indirectlyapproached lizards when approached rapidly, but shorter flightinitiation distances when approached slowly. Flight initiationdistance was shorter in the presence of food and during slowversus rapid approaches, but contrary to expectation, food presenceand approach speed did not interact. This would be explainedif cost curves are nonlinear or if they are parallel ratherthan intersecting when the predator reaches the prey. More empiricalwork is needed to determine which risk and cost factors actadditively and which act synergistically. The absence of interactionbetween the risk and cost factors suggests that cost curveswere nonlinear.     

Effects of risk assessment, predator behavior, and habitat on escape behavior in Columbian black-tailed deer

The relationship between preflight risk assessment by prey andthe escape behaviors they perform while fleeing from predatorsis relatively unexplored. To examine this relationship, a humanobserver approached groups of Columbian black-tailed deer (Odocoileushemionus columbianus), varying his behavior to simulate moreor less threatening behavior. We measured the focal deer's angleof escape, distance moved during flight, duration of trottingand stotting behavior, and change in elevation during flight.Analyses revealed positive relationships between the distancemoved during flight and the distance at which they fled. Whenflight was initiated when the approacher was close, deer fledrelatively shorter distances and took flight paths at more acuteangles, a property that would force a real predator to changedirection suddenly. Our results indicate that deer do not compensatefor allowing the observer to approach more closely by fleeinggreater distances. Rather, distance moved and flight initiationdistance are linked by level of reactivity and habituation:more reactive or less habituated deer both flee at a greaterdistance and move away to a greater distance during flight.More threatening behavior by the approacher led to longer durationsof rapid flight behavior (e.g., trotting and stotting), anddeer tended to flee uphill and into taller vegetation, usingthese landscape features as refuge from danger. Finally, weprovide the first evidence for Pitcher's untested "antiambush"hypothesis for the function of stotting and discuss its significance.In general, both preflight predator behavior and habitat featuresinfluence both duration and direction of escape.     

The influence of distance to burrow on flight initiation distance in the woodchuck, Marmota monax

We used woodchucks (Marmota monax) to test predictions of acost-benefit model of antipredator behavior that flight initiationdistance would increase with distance to refuge and with predatorapproach velocity. We also examined the effects of distanceto refuge and predator approach velocity on escape velocityand on both temporal and spatial margin of safety (expectedtime and distance between predator and burrow at the time ofthe woodchuck's arrival). The observer, assumed to be perceivedas a potential predator, approached juvenile woodchucks fromthe direction opposite to the burrow at a slow (1.24 m/s) orfast (1.79 m/s) walking pace. When the woodchuck started toflee, the observer recorded the woodchuck's distance from theobserver and from its burrow, the time spent running, and whetherthe woodchuck stopped before reaching its burrow. Flight initiationdistance increased consistendy with distance to the burrow overthe entire observed range (0–25 m) but was not significantlyaffected by observer approach velocity. Escape velocity wasnot significantly influenced by the observer approach velocityand was approximately constant over the range of 2–25m, but was slower for woodchucks less than 2 m from their burrows.Both temporal and spatial margins of safety increased with distancefrom the burrow. The temporal margin of safety increased withdistance from the burrow more rapidly for slow than for fastobserver approach velocity. Woodchucks fleeing from greaterthan 2 m usually stopped near the burrow before entering, butthose from closer distances usually entered directly. Theseresults support the assumption that antipredator behavior issensitive to the costs and benefits of alternative escape decisions.     

Flight initiation distance and escape behavior in the black redstart (Phoenicurus ochruros)

There are many anti‐predatory escape strategies in animals. A well‐established method to assess escape behavior is the flight initiation distance (FID), which is the distance between prey and predator at which an animal flees. Previous studies in various species throughout the animal kingdom have shown that group size, urbanization, and distance to refuge and body mass affect FID. In most species, FID increases if body mass, group size or distance to refuge decreases. However, how age and sexual dimorphism affect FID is rather unknown. Here, we assess the escape behavior and FID of the black redstart (Phoenicurus ochruros), a small turdid passerine. When approached by a human, males initiated flights later, that is allowing a closer approach than females. Males of this species are more conspicuous, and therefore, may exhibit aposematism to deter potential predators or are less fearful than females. Additionally, juveniles fled at shorter distances and fled to lower heights than adults. Lastly, concerning escape strategy, black redstarts, unless other passerine birds, fled less often into cover, but rather onto open or elevated spots. Black redstarts are especially prone to predation by ambushing predators that might hide in cover. Hence, this species most likely has a higher chance of escaping by fleeing to an open spot rather than to a potentially risky cover.     

When to come out from a refuge: risk-sensitive and state-dependent decisions in an alpine lizard

Prey often respond to predator presence by increasing theiruse of refuges. However, unfavorable thermal conditions in refugesmight entail physiological costs for an ectothermic prey. Thus,the decision of when to come out from a refuge should be optimizedby considering the expected fitness effects of diminution ofpredation risk with time, but also by considering the cost of theloss of time spent at optimal body temperature maximizing physiological functions.The model of Ydenberg and Dill describes the trade-off betweenrisk and cost for a prey fleeing to a refuge. We present a specialcase of this model to predict how emergence time from the refugein lizards or other ectotherms should vary as a function ofrisk of predation and thermal costs of refuge use. The analysesof the variation in emergence time from a refuge of Lacertamonticola lizards in the field under two different predation risklevels supported the predictions of the model. As predicted,time spent in the refuge was longer when the threat of the initialattack had been higher, and therefore the subsequent diminutionof risk was slower, but only when lizards emerged at the sameplace where they hid. When initial body temperature was high,some lizards decreased emergence time by emerging from a differentplace. In addition, the effects of thermal costs were more relevant inthe high-risk situation. Time spent in the refuge under highrisk increased when thermal conditions of the refuge were moresimilar to thermal conditions outside (i.e., physiological costsof refuge use were lower). We conclude that optimization ofrefuge-use strategies might help lizards cope with changes in predationrisk without incurring excessive physiological costs.     

Predation Risk and Opportunity Cost of Fleeing While Foraging on Plants Influence Escape Decisions of an Insular Lizard

Cost‐benefit models of escape behaviour predict how close a prey allows a predator to approach [flight initiation distance (FID)] based on cost of not fleeing (predation risk) and cost of fleeing (loss of opportunities). Models for FID have been used with some success to predict distance fled (DF). We studied effects of foraging opportunity cost of fleeing and examined differences between age‐sex groups in the omnivorous Balearic Lizard, Podarcis lilfordi. Balearic lizards forage on the ground for invertebrate prey and climb the thistle Carlina corymbosa to forage on its inflorescences. We studied escape behaviour in three experimental groups, with human beings as simulated predators: lizard foraging above ground on C. corymbosa, foraging on the ground away from thistles and on the ground with cut inflorescences. Flight initiation distance was shorter for lizards with cut inflorescences than for (1) lizards above ground due to the greater risk above ground due to conspicuousness of black lizards on yellow flowers; and (2) lizards on ground away from flowers due to the cost of leaving while feeding. The only age‐sex difference was slightly greater FID for adult males than subadults, presumably because larger adult males are more likely to be attacked by predators. Other potential factors affecting this difference are discussed. Experimental group and age‐sex group did not interact for FID or DF. Because lizards foraging on inflorescences above ground fled to the base of the plants to refuge provided by spiny thistle leaves, their DF was shorter than in the other groups, which fled across the ground, usually without entering refuge. DF did not differ between groups on the ground or among age‐sex groups. The predicted shorter DF for lizards with cut inflorescences than on ground without inflorescences did not occur. We hypothesize that the opportunity cost was small due to the abundance of blooming thistles and that DF may be less sensitive to opportunity cost than FID.     

Optimal escape theory predicts escape behaviors beyond flight initiation distance： risk assessment and escape by striped plateau lizards Sceloporus virgatus

Escape theory predicts that flight initiation distance (FID=distance between predator and prey when escape begins) is longer when risk is greater and shorter when escape is more costly. A few tests suggest that escape theory applies to distance fled. Escape models have not addressed stochastic variables, such as probability of fleeing and of entering refuge, but their economic logic might be applicable. Experiments on several risk factors in the lizard Sceloporus virgatus confirmed all predictions for the above escape variables. FID was greater when approach was faster and more direct, for lizards on ground than on trees, for lizards rarely exposed to humans, for the second of two approaches, and when the predator turned toward lizards rather than away. Lizards fled further during rapid and second consecutive approaches. They were more likely to flee when approached directly, when a predator turned toward them, and during second approaches. They were more likely to enter refuge when approached rapidly. A novel finding is that perch height in trees was unrelated to FID because lizards escaped by moving out of sight, then moving up or down unpredictably. These findings add to a growing body of evidence supporting predictions of escape theory for FID and distance fled. They show that two probabilistic aspects of escape are predictable based on relative predation risk levels. Because individuals differ in boldness, the assessed optimal FID and threshold risks for fleeing and entering refuge are exceeded for an increasing proportion of individuals as risk increases[Current Zoology 55(2):123-131,2009].     

Universal Optimization of Flight Initiation Distance and Habitat-Driven Variation in Escape Tactics in a Namibian Lizard Assemblage

Some aspects of escape predicted by theoretical models are intended to apply universally. For example, flight initiation distance (distance between an approaching predator and prey when escape begins) is predicted from predation risk and the costs of escaping. Escape tactics and refuge selection are not currently predicted by theoretical models, but are expected to vary with structural features of the habitat. One way of studying such variation is to compare aspects of antipredatory behavior among sympatric species that differ in habitat or microhabitat use. In an assemblage of lizards in northwestern Namibia, we conducted experiments to test predictions of escape theory for three risk factors in representatives of three families and observed escape tactics in additional species. As predicted by escape theory, flight initiation distance increased with directness of a predator's approach and predator speed in Agama planiceps, Mabuya acutilabris, and Rhotropus boultoni, and with distance from refuge in M. acutilabris. As predicted by theory, the probability of entering refuge increased with risk in R. boultoni. All available data indicate that flight initiation distance and refuge entry by lizards conform to theoretical predictions. Escape tactics varied greatly as a function of habitat type: (1) arboreal species fled up and around trees and sometimes entered tree holes; (2) saxicolous species used rock crevices as refuges, but differed in tactics prior to entering refuges; and (3) terrestrial species fled into bushes or other vegetation, often to the far sides of them. Some M. acutilabris entered small animal burrows or buried themselves in sand beneath bushes. Escape tactics varied even among congeners in Mabuya, highlighting the important effect of habitat structure on them. Although habitat partitioning has traditionally been viewed as favoring species coexistence, an interesting by‐product appears to be structuring of escape tactics in lizard communities.     

Influence of Some Potential Predation Risk Factors and Interaction between Predation Risk and Cost of Fleeing on Escape by the Lizard Sceloporus virgatus

Escape theory predicts that flight initiation distance (predator–prey distance when escape begins) increases as predation risk increases and decreases as cost of fleeing increases. Scant information is available about the effects of some putative predation risk factors and about interaction between simultaneously operating risk and cost of fleeing factors on flight initiation distance and distance fled. By simulating an approaching predator, I studied the effects of body temperature (BT), distance to nearest refuge, and eye contact with a predator, as well as simultaneous effects of predator approach speed and female presence/absence on escape behavior by a small ectothermic vertebrate, the lizard Sceloporus virgatus. Flight initiation distance decreased as BT increased, presumably because running speed increases as BT increases, facilitating escape. Distance to nearest refuge was unrelated to BT or flight initiation distance. Substrate temperature was only marginally related, and air temperature was not related to flight initiation distance. Eye contact did not affect flight initiation during indirect approaches that bypassed lizards by a minimum of 1 m, but an effect of eye contact found in other studies during direct approach might occur. Predator approach speed and presence of a female interactively affected flight initiation distance, which increased as speed increased and decreased when a female was present. In the presence of a female, flight initiation distance was far shorter than when no female was present. The high cost of forgoing a mating opportunity accounts for the interaction because the difference between female presence and absence is greater when risk is greater.     

When to Run and When to Hide: The Influence of Concealment,Visibility, and Proximity to Refugia on Perceptions of Risk

An animal's ability to avoid predation likely depends on its ability to detect approaching predators, conceal itself, and seek refuge or protection from predators. Habitat, especially vegetation structure, can influence all of these factors concurrently. Binary categorical assessments of habitat as ‘open’ or ‘closed’, however, confound at least two functions of habitat structure that could influence the perceived risk of predation: concealment, which functions to hide an individual, and visibility, which enhances detection of a potential predator. Both can influence predation risk independently and s imultaneously. In this study, we decoupled these functional properties of vegetation and studied the effects of concealment, visibility, and proximity to a refuge on the distance at which pygmy rabbits (Brachylagus idahoensis) fled from an approaching threat (flight initiation distance; FID). Concealment by vegetation decreased perceptions of risk; however, pygmy rabbits exhibited elevated risk at high levels of visibility, regardless of the amount of concealment. Proximity to burrow entrances also influenced perceptions of risk, such that risk was significantly lower when rabbits were on or near burrow systems. Disentangling the functional properties of habitat can provide a more comprehensive understanding of the factors that influence perceived risk and escape behaviors of prey and provide insight into how habitat structure mechanistically relates to predation risk.     

Repeated predatory attacks and multiple decisions to come out from a refuge in an alpine lizard

Prey often respond to predator presence by increasing theiruse of refuges. However, because the use of refuges may entailseveral costs, the decision of when to come out from a refugeshould be optimized. In some circumstances, if predators remainwaiting outside the refuge and try new attacks or if predator density increases, the prey may suffer successive repeated attacksin a short time. Successive attacks may represent an increasein the risk of predation, but the costs of refuge use alsomay increase with time spent in the refuge. Thus, prey shouldmake multiple related decisions on when to emerge from the refuge after each new attack. We simulated in the field repeatedpredatory attacks to the same individuals of the lizard Lacertamonticola and specifically examined the variation in successivetimes to emergence from a refuge under different thermal conditions(i.e., different costs of refuge use). The results showed thatrisk of predation but also thermal costs of refuge use affectedthe emergence decisions. Lizards increased progressively theduration of time spent in the refuge between successive emergencetimes when the costs of refuge use were lower, but tended tomaintain or to decrease the duration of time spent in the refugebetween successive emergence times when cost of refuge useincreased. Additionally, lizards that entered the refuge withhigher body temperatures had overall emergence times of longer duration. Optimization of refuge use and flexibility in theantipredator responses might help lizards to cope with increasedpredation risk without incurring excessive costs of refugeuse.     

Costs of Refuge Use Affect Escape Decisions of Iberian Rock Lizards Lacerta monticola

Theoretical models of anti-predator escape behaviour suggest that prey may adjust their escape response such that the optimal flight distance is the point at which the costs of staying exceed the costs of fleeing. Anti-predatory decisions should be made based also on consequences for long-term expected fitness, such as the costs of refuge use. For example, in lizards, the maintenance of an optimal body temperature is essential to maximize physiological processes. However, if unfavourable thermal conditions of refuges can decrease the body temperature of lizards, their escape decision should be influenced by refuge conditions. Analyses of the variation in flight distances and emergence latency from a refuge for the lizard Lacerta monticola under two different predation risk levels, and their relationship with the thermal environment, supported these predictions. When risk increased, lizards had longer emergence latencies, and thus costs of refuge use increased (a greater loss of time and body temperature). In the low-risk situation, lizards that were farther from the refuge had longer flight distances, whereas thermal conditions were less important. When risk increased, lizards had longer flight distances when refuges were farther off, but also when the external heating rate and the refuge cooling rate were lower. The results suggest that, in addition to the risk of predation, expected long-term fitness costs of refuges can also affect escape decisions.     

Anti-Predator Behavioral Responses of Mosquito Pupae to Aerial Predation Risk

Aquatic insects have two potential sources of predation risk: aquatic predators and aerial predators. Our goal was to assess anti-predator responses of Culex pipiens to aerial predation. By simulating predator attacks, we assessed (a) the distance fled in relation to depth and group size, (b) the distribution of individuals at different depths, and (c) the duration of surfacing events to obtain air in scenarios with varying predation risk. Pupae located closer to the surface fled deeper into the water, and the number of conspecifics decreased the distance fled. When the risk of predation increased, more individuals were found deeper in the water column, and the interval between two consecutive surfacing events increased. Culex pipiens shows a trade-off between avoiding aerial predation and maintaining oxygen acquisition, which may be regulated by the need to conserve energy reserves.     

Influence of predation pressure on the escape behaviour of Podarcis muralis lizards

Relationships between predator avoidance behaviour and predation pressure were investigated in the wall lizard, Podarcis muralis. The wariness of lizards belonging to high (1185m) and low elevation (308m) populations under two different predation pressure levels was compared. Wall lizards belonging to the lowland population experienced greater predation pressure than those belonging to the highland population. Lizards belonging to the population under higher predation pressure had higher frequency of refuge use, and had longer flight initiation distances (i.e. the distance lizards allowed the observer to approach before fleeing). In contrast, neither the distance fled (i.e. the total distance they fled in one continuous movement from the lizard's initial position until hiding or stopping at a safe distance) nor the distance to the nearest refuge were significantly different between populations. Escape responses were independent of ambient temperature in the lowland population, but animals belonging to the highland population had longer flight initiation distances when the ambient temperatures were higher. These findings suggest that predator avoidance behaviour may vary with predation pressure.     

Dynamic Risk Assessment: Prey Rapidly Adjust Flight Initiation Distance to Changes in Predator Approach Speed

The pre‐eminent model of flight initiation distance assumes that the function relating predation risk to distance between predator and prey is constant. However, the risk–distance function can change dramatically during approaches by predators. Changes in predator behavior during approach and in availability of benefits (e.g. food or potential mates) may alter risks and/or costs during encounters. Thus, prey should be able to respond appropriately to changes in cues to risk, such as predator approach speed. Under the assumption that prey assess risk in real time, it was predicted that flight initiation distance (distance between predator and prey when escape begins) decreases when approach speed increases and increases when approach speed decreases during an encounter. Effects of single, abrupt changes from slower to faster approach or the reverse were studied in a lizard, Anolis lineatopus. Flight initiation distances were determined solely by final approach speed, being nearly identical for: (1) continuously fast approaches and approaches initially at the slower and finally at the faster speed and (2) for continuously slower approaches and approaches initially at faster and finally at slower speed. Escape should be adjusted to match changes in risk and cost caused by changes in predator behavior, ability to escape, and costs of escape as attacks unfold. A recent model by Broom and Ruxton [Behavioural Ecology (2004) vol. 16, pp. 534—540] predicts that cryptic prey should stay motionless until detected, then flee immediately. Our results suggest that current escape models can be applied to prey escape strategies when cues to risk change, by assuming that prey base decisions on the current relationship between risk and distance. Empirical studies are needed to test predictions concerning continuous risk assessment.     

Optimal flight initiation distance

Decisions regarding flight initiation distance have received scant theoretical attention. A graphical model by Ydenberg and Dill (1986. The economics of fleeing from predators. Adv. Stud. Behav. 16, 229-249) that has guided research for the past 20 years specifies when escape begins. In the model, a prey detects a predator, monitors its approach until costs of escape and of remaining are equal, and then flees. The distance between predator and prey when escape is initiated (approach distance = flight initiation distance) occurs where decreasing cost of remaining and increasing cost of fleeing intersect. We argue that prey fleeing as predicted cannot maximize fitness because the best prey can do is break even during an encounter. We develop two optimality models, one applying when all expected future contribution to fitness (residual reproductive value) is lost if the prey dies, the other when any fitness gained (increase in expected RRV) during the encounter is retained after death. Both models predict optimal flight initiation distance from initial expected fitness, benefits obtainable during encounters, costs of escaping, and probability of being killed. Predictions match extensively verified predictions of Ydenberg and Dill's (1986) model. Our main conclusion is that optimality models are preferable to break-even models because they permit fitness maximization, offer many new testable predictions, and allow assessment of prey decisions in many naturally occurring situations through modification of benefit, escape cost, and risk functions.     

Cost/benefit analysis of group and solitary resting in the cowtail stingray, Pastinachus sephen

Unless a safe refuge is found where predation threats are negligible,resting poses risks for many animals, necessitating risk managementstrategies. The adult cowtail stingray (Pastinachus sephen)of Shark Bay, Western Australia, is a solitarily foraging animalthat facultatively groups when resting on shallow, inshore sandflats. We hypothesized that environmental conditions influencethe propensity of cowtails to group due to the limited abilityto detect predators visually in certain conditions. We thenexplored the possible benefits of grouping, such as bodily protection,early warning, and predator confusion, in conjunction with potentialgrouping costs, such as increased interference when initiatingflight and decreased escape speeds. Our study revealed thatin poor underwater visibility (due to turbidity and/or low ambientlight levels), cowtails primarily rest in small groups (threerays). Tests of flight initiation distance to a mock predatordemonstrated that solitary cowtail escape distances are significantlyshorter in poor than in good underwater visibility conditions.As to grouping benefits, filmed boat transects revealed thatcowtails most often arrange themselves in a rosette position,possibly as a means to protect their bodies and expose theirtails. The first cowtail in a group initiates flight to a mockpredator at a significantly greater distance than a solitarycowtail, and grouped cowtails escape an approaching boat ina significantly more cohesive manner than a simulated groupof escaping individual rays. Grouped cowtails exhibit behaviorsthat would impede immediate flight after detection. As a result,grouped rays escape a boat at significantly slower speeds thansolitary cowtails. Results from this study demonstrate thatthe interplay between costs and benefits of grouped and solitaryresting under differing environmental conditions is driven bydifferences in perceived predation risk and ultimately reflectedin the facultative grouping behavior of this species.     

A reevaluation of the logic of pilferage effects, predation risk, and environmental variability on avian energy regulation: the critical role of time budgets

We studied the effect of pilferage rates, variation in foodencounter rate, and predation risk on cache and fat-storageregulation using dynamic programming. Previous predictionsthat small birds facing increased pilferage rates should cacheless and store more body fat are not generally supported. Instead,cache investment (caching rate or percent of food cached) is predicted to be unimodal, peaking at intermediate pilferagerates. This pattern is determined, in part, by pilferage-inducedchanges in time budgets: at low pilferage rates, a marginalincrease in pilferage rates can be offset by an increase incache investment. However, increased caching increases time allocated to both caching and foraging. The increased foragingis caused by the energetic costs of caching and by the lossof energy from the cache. Increased time spent caching andforaging in turn decreases time spent resting under low predationrisk. Above some threshold pilferage rate, the marginal valueof resting exceeds the marginal value of caching, and cacheinvestment declines with further increasing pilferage rates.These patterns hold for three levels of variation in food encounterrate: time-invariant, between-day, and within-day variation;they also hold across different mean rates of food encounter.We show that previous predictions concerning decreased energy-storagelevels with increased food abundance are not supported when there is between-day variation in mean food encounter ratesand food abundance increases only on "good" days. Finally,predation risk affects the predictions described above in twoways. First, these trends assume that the birds can rest ina predator-free refuge. If the refuge is not available, birdsare predicted to cache less at higher pilferage rates irrespectiveof the absolute level of pilferage. With the refuge in place,levels of predation risk affect the skew in the pilferage-rate/cachingfunction. As a result, the relative effect of predation riskon caching intensity varies with pilfer rate. At very low pilferrates, lowered predation risk causes more caching, but loweredpredation risk under high pilferage rates can lower caching intensity, contrary to previous predictions. Surprisingly, predationrisk has an appreciable effect on body mass only when the birdis predicted to cease caching (i.e., at the highest pilferrates); otherwise a change of two orders of magnitude in theprobability of encountering predators has little effect on body mass. Our results suggest that the tradeoffs associatedwith the joint regulation of internal energy stores and externallycached stores are more complicated than previous literaturewould indicate. Our results also show that we have underestimatedthe role that time budgets play in patterns of energy regulation.     

Effects of predator behavior and proximity on risk assessment by Columbian black-tailed deer

In predator-prey encounters, many factors influence risk perceptionby prey and their decision to flee. Previous studies indicatethat prey take flight at longer distances when they detect predatorsat longer distances and when the predator's behavior indicatesthe increased likelihood of attack. We examined the flight decisionsof Columbian black-tailed deer (Odocoileus hemionus columbianus)using an approaching human whose speed, directness of approach,directness of gaze, and simulated gun carrying varied. Deerfled at greater distances when approached more quickly and directly,and there was a concave-down quadratic trend in the relationshipbetween the distances at which the predator began its approachand at which the deer became alert (alert distance [AD]), indicatingthat deer have a zone of awareness beyond which there is a delayin detecting an approaching predator. Time spent assessing theapproacher (assessment time) was shorter during faster approachesand was positively related with AD. Deer fled at longer distancesand had shorter assessment times when they were already alertto the predator at the initiation of approach. Males fled atshorter distances than females when approached during the gun-holdingcondition, and males had shorter assessment times than femaleswhen the approacher averted his gaze. Such sex differences inrisk assessment might reflect male motivation during the matingseason as well as exposure to human hunting. We suggest thatrisk assessment is affected the by the predator's behavior,the state of awareness of the prey, and the distance at whichthey detect the predator.     

Quantifying Predation Risk for Refuging Animals: A Case Study with Golden Marmots

Although a variety of behaviors expose animals to some risk of predation, there is no accepted way to compare their relative risk. For animals that retreat to refugia when alarmed by predators, the proportion of time devoted to each out-of-refuge behavior multiplied by the total time required to return to a refuge can be used to compare a behavior's relative predation risk. Total time to return to a refuge is a function of both response time - the time required to respond to an increased risk of predation — and travel time — the time required to flee to a refuge once alarmed. Quantifying these components can illustrate how animals minimize exposure to predators. Golden marmots (Marmota caudata aurea) were a refuging prey species used to examine the utility of this measure and to understand how marmots minimized their risk of exposure to predation. Golden marmots devoted different amounts of time to looking, foraging, self-grooming, and playing. To estimate the behavior-specific time required to return to refugia, the location of different activities was noted and a behavior-specific travel time was calculated. Alarm calls were played back to marmots engaged in different behaviors to determine, in a standardized manner, if there were behavior-specific response times. Marmots appeared to minimize their predation risk by performing most behaviors close to refugia. Results suggest that foraging was the riskiest behavior, largely because marmots foraged far from refugia and spent about 30% of their time foraging. While sample sizes were small, results also suggested that play, a rare adult behavior, exposed animals to predation because of a relatively long response time.