Variation In Flight Initiation Distance Research Articles

Is flight initiation distance associated with longer-term survival in yellow-bellied marmots, Marmota flaviventer?

The distance at which animals move away from threats, flight initiation distance (FID), is often used to study antipredator behaviour and risk assessment. Variation in FID is explained by a variety of internal and external biotic and physical factors, including anthropogenic activities. Most prior studies focused on unidentified individuals, so our understanding of the fitness consequences of FID is relatively limited. We asked whether consistent individual differences in variation in flight initiation distance is associated with variation in summer survival and/or winter survival in an individually marked population of yellow-bellied marmots. We found no clear association between flight initiation distance and summer survival or winter survival. This suggests that FID decisions, while demonstrably optimizing current survival, may not have longer-term fitness consequences. Our results may be explained by the relatively modest repeatability of FID or it may have emerged from our attempt to explain longer-term measures of fitness. Future studies of the fitness consequences of personality traits should pay particular attention to the time interval between measuring the individuality of a trait and examining its fitness consequences.

Drivers of within- and among-individual variation in risk-taking behaviour during reproduction in a long-lived bird.

Plastic and selective mechanisms govern parental investment adjustments to predation threat. We investigated the relative importance of plasticity and selection in risk-taking propensity of incubating female common eiders Somateria mollissima facing unprecedented predation in SW Finland, Baltic Sea. Using a 12-year individual-based dataset, we examined within- and among-individual variation in flight initiation distance (FID), in relation to predation risk, nest detectability, individual traits and reproductive investment (NFID = 1009; Nindividual = 559). We expected females nesting in riskier environments (higher predation risk, lower nest concealment) to mitigate environmentally imposed risk by exhibiting longer FIDs, and females investing more in current reproduction (older, in better condition or laying larger clutches) to display shorter FIDs. The target of predation-adult or offspring-affected the mechanisms adapting risk-taking propensity; females plastically increased their FID under higher adult predation risk, while risk-avoiding breeders were predominant on islands with higher nest predation risk. Risk-taking females selected thicker nest cover, consistent with personality-matching habitat choice. Females plastically attenuated their anti-predator response (shorter FIDs) with advancing age, and females in better body condition were more risk-taking, a result explained by selection processes. Future research should consider predator type when investigating the fitness consequences of risk-taking strategies.

Resident birds are more behaviourally plastic than migrants

Species subjected to more variable environments should have greater phenotypic plasticity than those that are more restricted to specific habitat types leading to the expectation that migratory birds should be relatively more plastic than resident birds. We tested this comparatively by studying variation in flight initiation distance (FID), a well-studied antipredator behaviour. We predicted that variation in FID would be greater for migratory species because they encountered a variety of locations during their lives and therefore had less predictable assessments of risk compared to more sedentary species. Contrary to our prediction, we found that non-migratory species (sedentary) had greater variation in FID than migratory ones. Migratory and partially migratory birds had greater average FIDs than sedentary birds, suggesting that they were generally more wary. These results suggest that the predictability associated with not migrating permits more nuanced risk assessment which was seen in the greater variation in FID of sedentary bird species.

Empirical studies of escape behavior find mixed support for the race for life model.

Escape theory has been exceptionally successful in conceptualizing and accurately predicting effects of numerous factors that affect predation risk and explaining variation in flight initiation distance (FID; predator–prey distance when escape begins). Less explored is the relative orientation of an approaching predator, prey, and its eventual refuge. The relationship between an approaching threat and its refuge can be expressed as an angle we call the “interpath angle” or “Φ,” which describes the angle between the paths of predator and prey to the prey’s refuge and thus expresses the degree to which prey must run toward an approaching predator. In general, we might expect that prey would escape at greater distances if they must flee toward a predator to reach its burrow. The “race for life” model makes formal predictions about how Φ should affect FID. We evaluated the model by studying escape decisions in yellow-bellied marmots Marmota flaviventer, a species which flees to burrows. We found support for some of the model’s predictions, yet the relationship between Φ and FID was less clear. Marmots may not assess Φ in a continuous fashion; but we found that binning angle into 4 45° bins explained a similar amount of variation as models that analyzed angle continuously. Future studies of Φ, especially those that focus on how different species perceive relative orientation, will likely enhance our understanding of its importance in flight decisions.

Love thy prickly neighbor? Sea urchin density affects risk assessment in damselfish

In coral reef communities, sea urchins and reef fish have a variety of commensal relationships. However, if fish view urchins as a potential form of predator protection, then urchin presence should influence reef fish risk assessment. We investigated whether dusky damselfish (Stegastes nigricans) perceive burrowing urchins (Echinometra mathaei) as a form of predator protection by asking whether and how urchin presence explains variation in flight initiation distance, the distance a fish fled an approaching threat. We found that when individuals were subjected to a high-risk approach (i.e., one that started relatively close to the fish), and urchin density was high, dusky damselfish tolerated a closer approach than when subjected to high risk with low urchin density. However, when there was low risk and high urchin density, the damselfish fled sooner. We conclude that under high risk, damselfish perceive burrowing urchins as providing added security from approaching threats.

The effect of mobbing vocalizations on risk perception in common mynas (Acridotheres tristis)

Animals emit predator-elicited calls in response to potential predation threats. These vocalizations induce a variety of anti-predator behaviors in conspecific receivers ranging from moving away from predators (alarm calls) to rallying conspecifics to fend them off (mobbing calls). While much is known about the immediate response to alarm calls, less is known about how mobbing calls influence subsequent antipredator decisions. Mobbing calls stimulate harassment of a potential predator. Therefore we predicted that hearing a mobbing call would make animals less likely to immediately flee an approaching threat. To study the potential effect of mobbing vocalizations on risk assessment, we primed common mynas (Acridotheres tristis) with a series of different stimuli and studied the variation in their subsequent decisions to flee an approaching human by quantifying flight initiation distance (FID). We found that although mynas increased their rate of locomotion after hearing mobbing calls, their subsequent decision to flee was not influenced. We also found that an individual’s propensity to move and look explained some variation in FID. This suggests that while mobbing calls do not influence subsequent decisions to flee, they do affect subsequent behavior.

Structural complexity but not territory sizes influences flight initiation distance in a damselfish

The fear of predators can lead to behavioral changes in their prey, but animals must trade off defensive behavior against other compelling needs. For territorial species, responding to predators may be especially costly, because defense and escape are mutually incompatible. A growing literature documents risk assessment in fish, but a few studies have focused on extremely territorial fish, and nothing is known about how territory size, territorial interactions, habitat structural complexity, and life stage may modify risk assessment. We studied this in a damselfish (Stegastes fuscus) on coral reefs and measured risk assessment using flight initiation distance (FID). We found that only structural complexity explained variation in FID; fish in more complex habitats tolerated closer approach. Our study suggests that individuals in relatively more structurally complex territories are bolder than those that occur in less complex territories. Documenting the relative importance of these variables is important, because antipredator behavior influences not only the predator–prey relationship, but can also generate cascading effects, and influence the structure of the community and potentially entire ecosystems.

Should I stay, or should I go: Modeling optimal flight initiation distance in nesting birds.

Flight initiation distance (FID)–the distance at which an individual leaves in response to the approach of a perceived threat–provides a measurement of risk-taking behavior. If individuals optimize their FID, this distance should reflect the point at which the fitness resulting from leaving exceeds the fitness resulting from all other possible decisions. Previous theory of FID has often been aimed at explaining this behavior in foraging individuals. Yet flight initiation in response to approaching threats occurs in a range of contexts that might influence optimal behavior. In breeding individuals, risk-taking decisions that are made at a location of offspring care (e.g., a nest or den) can have significant effects on fitness. Here, we develop a theoretical model of distances at which a parent bird flushes from a nest in response to an approaching threat. We estimate parent fitness with regards to characteristics of the parent (reproductive values, detection distance, and cost of lost parental care cost), the nest (concealment and accessibility), and the approaching predator (detection capability and predation success), developing a dichotomous scenario between staying at the nest or leaving at varying distances. Using a generalized comparison of the benefits of leaving versus staying, we find that increasing costs of lost parental care, probability of predation of the parent due to fleeing, or current reproductive value lead to more instances of staying at the nest. In a complementary approach with specified parameters based on biologically-informed factors that likely influence a predator-prey encounter, we find that increasing the current reproductive value, concealment of the nest, or costs of lost parental care decrease optimal FID and can lead to the parent staying at the nest. Other factors, such as increasing residual reproductive value, predation success, and predator capability of detecting the nest, increase optimal FID with some instances of costs of fleeing being so great that staying becomes an optimal strategy. Our theory provides a framework to explain variation in FID among nesting species and individuals and could provide a foundation for future empirical investigations of risk-taking behavior.

Are the big and beautiful less bold? Differences in avian fearfulness between the sexes in relation to body size and colour

AbstractConspicuousness towards predators may influence escape behaviour (or ‘fearfulness’) among animals, with more conspicuous species initiating escape behaviour earlier. Among birds, for example, body size and colour may influence differences in escape behaviour between species, and possibly between the sexes of dimorphic species. We examined 19 bird species with varying degrees of body size and colour dimorphism (including individually marked and sexed monomorphic species), to examine whether these two potential measures of conspicuousness influence sex differences in flight‐initiation distance (FID). Starting Distance (the distance at which an observer commenced approaching a bird, which is an artefact of investigator behaviour; SD) was not correlated with dimorphism, so we used phylogenetically controlled models which explored the correlation between dimorphism and FID. Modelling indicated that only sex differences in SD correlated with sex differences in FID in these birds, and that dimorphism in either plumage or body size does not apparently correlate with sex differences in FID. These results suggest that, among the 19 bird species investigated, apparent differences in the conspicuousness to predators between the sexes do not influence escape behaviour. This suggests that either conspicuousness to predators does not influence escape distances in these species, or that sex differences in conspicuousness were too subtle to result in variation in FIDs.

Vivid birds do not initiate flight sooner despite their potential conspicuousness

Abstract The distance from an approaching threat at which animals initiate flight -- flight-initiation distance (FID) -- is a sensitive metric of variation in risk, but the effects on FID associated with the risk of possessing highly detectable external coloration are unknown. We tested whether variation in the degree of plumage vividness in birds explained variation in flight-initiation distance. After controlling for body mass, the distance at which the experimental approach began, and phylogenetic relatedness, plumage vividness was not a predictor of FID. Contrary to the expectation that vividness affects risk, and therefore risk assessment, these results suggest that birds do not compensate for greater visual conspicuousness by fleeing sooner from approaching threats.

Hawk models, hawk mimics, and antipredator behavior of prey

Prey typically respond to potential predators by taking flight. This results in an optimal flight initiation distance (FID) at which the risk of remaining and the cost of flight are equal. Thus, FID is strongly negatively correlated with susceptibility to predation by the sparrowhawk Accipiter nisus across species of small European birds. However, not everything that looks like a hawk is in fact a hawk. Aggressive mimicry arises from the resemblance between a dangerous model such as a predatory hawk and an innocuous mimic such as a cuckoo that makes errors made by individuals that encounter models and mimics potentially dangerous and life threatening. A prime example of such aggressive mimicry is the hawk-like appearance of common cuckoos Cuculus canorus and other cuckoos. If mimicry is efficient, we should expect that species of small birds that are prey of hawks and hosts of cuckoos react just as strongly to a cuckoo as to the presence of a dangerous model like a sparrowhawk. We used FID of small birds as a measure of the reaction of prey to models and mimics, predicting that FID would be negatively related to susceptibility to predation and positively to risk of cuckoo parasitism. Both susceptibility to sparrowhawk predation and rate of brood parasitism by the common cuckoo independently explained variation in FID, consistent with the expectation that both hawks and cuckoos have imposed significant selection pressures on FID and that species of small birds perceive cuckoos as true mimics of hawks.

Bird flight initiation distances in relation to distance from human settlements in a Tanzanian floodplain habitat

Human activity affects wildlife in many ways, but there have been few studies of how wildlife behavioural responses to human disturbance vary with distance from centres of human activity. Theory suggests that fear responses may be either higher in areas with high disturbance (disturbance avoidance) or lower in such areas (e.g. due to habituation). We used flight initiation distance (FID) to study how fear responses of 16 bird species varied with distance from villages (range 0.1–11.6 km) within the Ramsar site of Kilombero Valley, Tanzania. A linear model indicated that FID was not related to distance from villages, but varied between habitats. However, a piecewise linear model (linear response up to 2 km, flat response >2 km from villages) provided a better fit and suggested that there may be a small decrease in FID close to human settlements, in particular for the Common Bulbul (Pycnonotus barbatus) and a few other species, although the majority of species still showed little change in FID with distance from human settlements. Our results suggest that a few species may respond to human disturbance with a decreased FID, whereas the majority of species showed little variation in FID in relation to distance from human settlements, and may therefore be negatively affected by increasing frequency of human disturbance.

Malaria parasites, immune challenge, MHC variability, and predator avoidance in a passerine bird

Several hypotheses predict a relationship between parasite burden and risk-taking behavior, but the underlying causal mechanisms are poorly understood due to the scarcity of experimental studies and the neglected focus on immune defense. Here, in 3 sets of field studies on the collared flycatcher, Ficedula albicollis, we investigated how among-male variation in flight initiation distance (FID, the distance at which an individual flee a potential predator) is linked to among-male variation in health status. First, we correlatively assessed the relationship between FID and the prevalence of haemosporidian blood parasites. We found no difference in risk-taking behavior between parasitized and nonparasitized individuals rejecting a hypothesis that predicts that malaria infection status affects the costs of predator avoidance. Second, we performed an immune challenge experiment, in which randomly chosen birds were injected with a novel antigen (sheep red blood cell) and their change in FID was compared with birds that received a placebo treatment. This experiment revealed no evidence for the immunological treatment affecting risk-taking behavior, thus we failed to obtain support for the hypothesis that posits that immediate health status mediates decisions about when to flee a predator. Finally, we detected a negative relationship between the number of alleles of the major histocompatibility complex and FID. This result, in concordance with the above negative results, supports the “avoidance” hypothesis that states that only individuals with efficient immune defense machinery are able to bear the costs of risk-taking that can emerge through the increased infection rates of risk-taker individuals.

The ontogeny of escape behavior, locomotor performance, and the hind limb in Sceloporus woodi

Flight initiation distance describes the distance at which an animal flees during the approach of a predator. This distance presumably reflects the tradeoff between the benefits of fleeing versus the benefits of remaining stationary. Throughout ontogeny, the costs and benefits of flight may change substantially due to growth-related changes in sprint speed; thus ontogenetic variation in flight initiation distance may be substantial. If escape velocity is essential for surviving predator encounters, then juveniles should either tolerate short flight initiation distances and rely on crypsis, or should have high flight initiation distances to remain far away from their predators. We examined this hypothesis in a small, short-lived lizard (Sceloporus woodi). Flight initiation distance and escape velocity were recorded on an ontogenetic series of lizards in the field. Maximal running velocity was also quantified in a laboratory raceway to establish if escape velocities in the field compared with maximal velocities as measured in the lab. Finally a subset of individuals was used to quantify how muscle and limb size scale with body size throughout ontogeny. Flight initiation distance increased with body size; larger animals had higher flight initiation distances. Small lizards had short flight initiation distances and remained immobile longer, thus relying on crypsis for concealment. Escape velocity in the field did not vary with body size, yet maximum velocity in the lab did increase with size. Hind limb morphology scaled isometrically with body size. Isometric scaling of the hind limb elements and its musculature, coupled with similarities in sprint and escape velocity across ontogeny, demonstrate that smaller S. woodi must rely on crypsis to avoid predator encounters, whereas adults alter their behavior via larger flight initiation distance and lower (presumably less expensive) escape velocities.

Developing an evolutionary ecology of fear: how life history and natural history traits affect disturbance tolerance in birds

When approached by humans, virtually all species flee, but we lack an understanding of the factors that influence flight response among species. Understanding this variation may allow us to understand how ‘fear’ structures communities, as well as to predict which species are likely to coexist with humans. I used flight initiation distance (FID) as a comparative metric of wariness and examined the relative importance of life history and natural history traits in explaining variation in FID in 150 species of birds. In a series of comparative analyses, I used independent contrasts to control for phylogenetic similarity and regressed continuous life history traits against flight initiation distance. Body size had a large and significant effect in explaining variation in flightiness: larger species initiated flight at greater distances than smaller species. After controlling for variation explained by body size, there was a nonsignificant positive relation between the age of first reproduction and FID. There were no relations between FID and clutch size, number of days spent feeding young, longevity, or habitat density. I used concentrated changes tests to look for evidence of coevolution between flightiness and dichotomous traits. Flightiness evolved multiple times and some clades were flightier than others. Flightiness was more likely to evolve in omnivorous/carnivorous species and in cooperatively breeding species. These results suggest that body size and age of first reproduction are important in explaining variation in disturbance tolerance in birds, and that species that capture live prey and those that are highly social are relatively wary. The results suggest a novel mechanism of how anthropogenic disturbance may contribute to extinction.