Using flight initiation distance to evaluate responses of colonial‐nesting Great Egrets to the approach of an unmanned aerial vehicle

Remote‐controlled, unmanned aerial vehicles (UAVs) can be used to collect information in difficult‐to‐access places while potentially minimizing human disturbance. These devices have been widely used in a variety of ecological and behavioral studies in recent years, but additional study is needed to assess the magnitude of disturbance they cause to birds. We examined the responses of Great Egrets (Ardea alba) to a UAV in a breeding colony in Louisiana in 2016 where isolated patches of common reed (Phragmites australis) were used as nest sites by multiple breeding pairs. We examined the flush responses and flight initiation distances (FIDs) of nesting adults to the direct vertical approach of a UAV. Incubating adults were more likely to flush from nests and flushed at greater distances when approached by a UAV than adults with nestlings, suggesting that adult assessment of risk was based on the greater reproductive value of nestlings. We observed fewer flush responses and calculated lower set‐back distances using a UAV to approach nesting Great Egrets (~50 m) than set‐back distances calculated using traditional methods of approach (e.g., walking or boating; 87–251 m). We found that FIDs were shorter when more adults were present in nesting patches, suggesting that the perception of predation risk may be based in part on the reactions of other birds. Our results suggest that UAVs may be a useful alternative for monitoring colonial‐nesting waterbirds. However, our analyses were based exclusively on behavioral observations. Additional studies of the physiological responses of birds to the approach of UAVs are needed to better understand the stress responses of birds to these devices.     

Managing human disturbance: factors influencing flight-initiation distance of birds in a West African nature reserve

Escape behaviour in response to perceived predators can be employed as a guide when designating protected areas around sensitive bird species to minimise the impact of human disturbance. A key measure of escape response is flight-initiation distance (FID), the distance at which a prey animal initiates its escape when approached by a potential predator. We tested the predictions of optimal escape theory by determining the factors that influence FID of bird species in a Nigerian reserved area and its surrounding habitats, and so the potential utility of FID in managing human disturbance on birds, for the first time within a West African context. We tested how FID varied with group size, proximity to vegetation acting as protective cover, levels of human use, and survival rate, and whether these relationships varied by species. We collected 504 FIDs for seven bird species in Amurum Forest Reserve and its surrounding habitats (Jos, Nigeria). The FID was lower in larger groups and when species were closer to protective cover. The FID was lower outside of the protected area because animals in sites with higher levels of human presence and use may become habituated. The FID was higher for species with higher survival, being consistent with predictions from life history theory. Overall, birds perceived humans as a potential threat and responded in accordance to the predictions of optimal escape theory, with FID increasing with increased cost of staying. Reserve managers in Africa could use species- and context-specific FIDs to designate buffer distances for the protection of wildlife from human disturbance.     

White-Tailed Deer Response to Vehicle Approach: Evidence of Unclear and Present Danger

The fundamental causes of animal-vehicle collisions are unclear, particularly at the level of animal detection of approaching vehicles and decision-making. Deer-vehicle collisions (DVCs) are especially costly in terms of animal mortality, property damage, and safety. Over one year, we exposed free-ranging white-tailed deer (Odocoileus virginianus) to vehicle approach under low ambient light conditions, from varying start distances, and vehicle speeds from 20 km/h to approximately 90 km/h. We modeled flight response by deer to an approaching vehicle and tested four hypotheses: 1) flight-initiation distance (FID) would correlate positively with start distance (indicating a spatial margin of safety); 2) deer would react to vehicle speed using a temporal margin of safety; 3) individuals reacting at greater FIDs would be more likely to cross the path of the vehicle; and 4) crossings would correlate positively with start distance, approach speed, and distance to concealing/refuge cover. We examined deer responses by quantiles. Median FID was 40% of start distance, irrespective of start distance or approach speed. Converting FID to time-to-collision (TTC), median TTC was 4.6 s, but uncorrelated with start distance or approach speed. The likelihood of deer crossing in front of the vehicle was not associated with greater FIDs or other explanatory variables. Because deer flight response to vehicle approach was highly variable, DVCs should be more likely with increasing vehicle speeds because of lower TTCs for a given distance. For road sections characterized by frequent DVCs, we recommend estimating TTC relative to vehicle speed and candidate line-of-sight distances adjusted downward by (1-P), where P represents our findings for the proportion of start distance by which >75% of deer had initiated flight. Where road design or conservation goals limit effectiveness of line-of-sight maintenance, we suggest incorporation of roadway obstacles that force drivers to slow vehicles, in addition to posting advisory speed limits.     

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.     

Effects of Single‐ and Mixed‐Species Group Composition on the Flight Initiation Distances of Plains and Grevy's Zebras

Zebras, as prey species, attend to the behavior of nearby conspecifics and heterospecifics when making decisions to flee from predators. Plains zebras (Equus quagga) and Grevy's zebras (E. grevyi) frequently form mixed‐species groups in zones where their ranges overlap in Kenya. Although anecdotal observations suggest that Plains zebras are more flighty around humans than Grevy's zebras are, this has not been empirically confirmed, and relatively little is known about how they may influence each other's flight behavior. We addressed these questions by examining the flight initiation distances (FIDs) of Plains and Grevy's zebras in single‐species and mixed‐species groups from an approaching human. One target individual per group was approached steadily on foot, with start distance, alert distance, and FID recorded from this target. Using start distance and alert distance separately as covariates, 22 Plains zebras in single‐species groups exhibited a significantly longer mean FID than 15 Grevy's zebras in single‐species groups. The FIDs of 7 Plains zebras and 5 Grevy's zebras tested in mixed‐species groups were virtually equivalent and intermediate to those of Plains and Grevy's zebras in single‐species groups, suggesting a bidirectional moderating influence of heterospecifics on risk assessment. This effect was most pronounced for Plains zebras in mixed‐species groups that exhibited an FID that was significantly shorter than that of Plains zebras in single‐species groups. Our findings underscore the importance of recognizing that related equids may be differently impacted by anthropogenic stress.     

Behavioral responses of nesting birds to human disturbance along recreational trails

ABSTRACT The presence of recreational trails can impact breeding birds either indirectly by altering habitat or the movement patterns of predators or directly if the presence of humans disturbs birds. We examined the behavioral responses of nesting female Northern Cardinals (Cardinalis cardinalis) to human disturbance using both experimental and observational approaches. From April to August 2006 and 2007, we monitored Northern Cardinal nests in 18 riparian forests in Ohio, USA. Two experimental trials were conducted at each nest (N= 63), with Flight Initiation Distance (FID, the distance at which a bird flushed from the nest) recorded as we approached nests by walking directly toward them and by walking along trails located variable distances from nests. We also measured flight initiation distance (FID) when nests were approached during routine nest checks (N= 160). Cardinals were six times more likely to flush when nests were approached directly, and females on higher nests were less likely to flush regardless of distance to trail. FID was not significantly influenced by the distance of nests from trails. We found no association between nest survival and the tendency of birds to flush. Rather, nest survival was best explained by nest height. Thus, our findings suggest that the responses of birds to human use of recreational trails have only short‐term effects, with no apparent effects of on nest survival. Because the reaction of birds to humans in our study depended on how nests were approached, studies where FID is used as an indicator of sensitivity to human disturbance and is determined by direct approaches may overestimate the potential impact of trails on nesting birds.     

Inter-individual variability in fear of humans and relative brain size of the species are related to contemporary urban invasion in birds

Background

Urbanization is the most prevailing cause of habitat transformation worldwide, differing from others by its intense levels of human activity. Despite its obvious impact on wildlife, it is still unclear why and how some species are able to adapt to urban settings. One possibility is that fear of humans and vehicles could preclude most species from invading cities. Species entering urban environments might be those that are more tolerant of human disturbance (i.e., tame species). Alternatively or in addition, urban invaders could be a fraction of variable species, with “tame” individuals invading urban habitats and other individuals remaining in rural areas.

Methodology

Using the contemporary urban invasion by birds in a recently established South American city, we tested both hypotheses by relating interspecific differences in invasiveness to their flight initiation distances (i.e., the distances at which birds flee from approaching cars, FID), as well as to their relative brain size (RBS), a correlate of measures of behavioral flexibility.

Principal Findings

Urban invasiveness was not significantly related to species'' average rural FIDs but positively related to their RBS and inter-individual variability in FID. Moreover, FIDs were consistently lower in urban than in rural conspecifics, and the FIDs of urban individuals were within the lower-range distribution of their rural conspecifics. RBS indirectly influenced urban invasion through its positive effect on inter-individual variability in FID.

Conclusions/Significance

Urban invaders do not appear to be individuals from apparently tame species, but rather tame individuals from species with a variable response regarding fear of people. Given the positive relationship between RBS and inter-individual variability in FID, our results suggest that behavioural flexibility should be regarded as a specific trait encompassing variability among individuals. Further research is needed to ascertain the neurophysiological mechanisms underlying the relationship between brain size and inter-individual variability in behavioural traits.     

Life history,predation and flight initiation distance in a migratory bird

Life‐history trade‐offs occur as a consequence of the compromise between maximization of different components such as the size and the number of clutches. Flight initiation distance (FID) potentially constitutes a general proximate factor influencing such trade‐offs reflecting the risks that individuals take. Therefore, greater investment in reproduction occurs at a higher risk of death, resulting in selection for efficient flight morphology. I analysed long‐term data on FID in a population of barn swallows Hirundo rustica during 1984–2013 with 2196 records of FID for 1789 individuals. FID had a repeatability of 0.62 (SE = 0.04) and a heritability of 0.48 (SE = 0.07). FID varied between individuals and sites, and it increased over time as climate ameliorated. FID showed a U‐shaped relationship with age, with young and very old individuals having the longest FIDs. Barn swallows that arrived early from spring migration, started to breed early and produced many fledglings had the longest FID. Individuals with the longest tails had the longest FID, and individuals with the shortest aspect ratios and wing loadings had the longest FID. Individuals that died from predation had shorter FID than survivors. These findings are consistent with the hypothesis that FID relates directly to life history, with longer FIDs being associated with smaller levels of risk‐taking.     

Behavioral and physiological adjustments to new predators in an endemic island species, the Galápagos marine iguana

For the past 5 to 15 million years, marine iguanas (Amblyrhynchus cristatus), endemic to the Galápagos archipelago, experienced relaxed predation pressure and consequently show negligible anti-predator behavior. However, over the past few decades introduced feral cats and dogs started to prey on iguanas on some of the islands. We investigated experimentally whether behavioral and endocrine anti-predator responses changed in response to predator introduction. We hypothesized that flight initiation distances (FID) and corticosterone (CORT) concentrations should increase in affected populations to cope with the novel predators. Populations of marine iguanas reacted differentially to simulated predator approach depending on whether or not they were previously naturally exposed to introduced predators. FIDs were larger at sites with predation than at sites without predation. Furthermore, the occurrence of new predators was associated with increased stress-induced CORT levels in marine iguanas. In addition, age was a strong predictor of variation in FID and CORT levels. Juveniles, which are generally more threatened by predators compared to adults, showed larger FIDs and higher CORT baseline levels as well as higher stress-induced levels than adults. The results demonstrate that this naive island species shows behavioral and physiological plasticity associated with actual predation pressure, a trait that is presumably adaptive. However, the adjustments in FID are not sufficient to cope with the novel predators. We suggest that low behavioral plasticity in the face of introduced predators may drive many island species to extinction.     

Avian Risk Assessment: Effects of Perching Height and Detectability

We studied two components of predator risk assessment in birds. While many species are limited to seeking safety under cover or under ground, some birds can fly away from their predators and escape to trees. If birds in fact ‘feel’ safer (e.g. perceive less risk) in trees, we would expect them to tolerate closer approach by a potential terrestrial predator. Another component of safety is at which point the animal detects an approaching threat, which we expected to increase with eye size, assuming eye size is a surrogate for visual acuity. We used the distance birds moved away from an approaching human [flight initiation distance (FID)] as a metric to determine whether birds associated a lower risk of predation by being in trees, and we used the distance at which birds first displayed alert behaviors from an approaching human (alert distance) to determine if birds with larger eyes had higher detection distances. Although some species were affected by tree height, we found no clear pattern that birds assessed themselves to be at a lower risk of predation when they were ≥3 m above the ground compared with being <3 m above ground. In the 10 species for which height had any significant effect on FID, birds ≥3 m off the ground had greater FIDs in six species, but the remaining three species had the opposite response. While we found a significant positive relationship between eye size and alert distance in 23 species, the relationship was not present in a phylogenetic analysis using independent contrasts, which suggests that the apparent relationship was influenced strongly by the association between the studied species. Together, these results suggest that birds do not obviously associate being in a tree with safety, and that variations in visual acuity, per se, cannot be used as a general indicator of differences in alert distances, as previously suggested in the literature.     

鸟类惊飞距离及其影响因素

惊飞距离(FID)是指捕食者(包括人类)接近目标个体并导致其逃避时,捕食者与目标个体之间的距离。惊飞距离能很好地衡量动物个体在特定环境下的恐惧反应和风险权衡,是研究动物逃避行为的常用指标,并为物种保护提供科学依据。鸟类是研究逃避行为的理想对象,本文综述了影响鸟类惊飞距离的各种因素,可分为3类:栖息地因素(距隐蔽处的距离和生境开阔度等)、鸟类自身因素(生活史、体型和群体大小等)以及与捕食者相关的因素(捕食者的接近方向和速度等)。城市化也会影响鸟类的惊飞距离,导致城市中的鸟类通常比乡村生境的同种鸟类拥有更短的惊飞距离。习惯化、适应和生境选择是解释惊飞距离城乡差异的3种假说。研究鸟类的惊飞距离及其影响因素,有助于理解鸟类的逃避行为及其风险权衡机制,为物种保护中设立合理的缓冲区域及制定有效的保护管理措施提供科学依据。目前国内有关鸟类惊飞距离的研究多为行为观察和单一因素的影响,有待从不同因素的交互作用角度探讨鸟类的逃避行为并用于物种保护。     

The Effect of Human Presence and Human Activity on Risk Assessment and Flight Initiation Distance in Skinks

Antipredator behavior and risk assessment of many species are affected by the presence of humans and their activities. Previous studies have largely been conducted on birds and mammals and relatively less is known about human impacts on reptiles. We used flight initiation distance (FID) as a measure of risk assessment in inland blue‐tailed skinks (Emoia impar) and tested the direct and indirect effects of humans on risk assessment. We first examined the effects of varying levels and types of human disturbance and activity on skink FID. We found that skinks flushed at significantly longer distances in areas with the least human activity. We then tested the degree to which skinks are able to discriminate different numbers of humans by comparing FID across three different types of approaches. Skinks did not significantly differentiate between a single approacher and a single approacher coming from a group of two other people, but did flush at greater distances when approached by three people simultaneously. Although skinks are not directly harvested or harassed by humans, they have refined human discrimination abilities. Overall, skinks habituate to a variety of human activities and perceive a larger threat when the number of human approachers is greater.     

Behavioral and physiological adjustments to new predators in an endemic island species,the Galápagos marine iguana

For the past 5 to 15 million years, marine iguanas (Amblyrhynchus cristatus), endemic to the Galápagos archipelago, experienced relaxed predation pressure and consequently show negligible anti-predator behavior. However, over the past few decades introduced feral cats and dogs started to prey on iguanas on some of the islands. We investigated experimentally whether behavioral and endocrine anti-predator responses changed in response to predator introduction. We hypothesized that flight initiation distances (FID) and corticosterone (CORT) concentrations should increase in affected populations to cope with the novel predators. Populations of marine iguanas reacted differentially to simulated predator approach depending on whether or not they were previously naturally exposed to introduced predators. FIDs were larger at sites with predation than at sites without predation. Furthermore, the occurrence of new predators was associated with increased stress-induced CORT levels in marine iguanas. In addition, age was a strong predictor of variation in FID and CORT levels. Juveniles, which are generally more threatened by predators compared to adults, showed larger FIDs and higher CORT baseline levels as well as higher stress-induced levels than adults. The results demonstrate that this naive island species shows behavioral and physiological plasticity associated with actual predation pressure, a trait that is presumably adaptive. However, the adjustments in FID are not sufficient to cope with the novel predators. We suggest that low behavioral plasticity in the face of introduced predators may drive many island species to extinction.     

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.     

European birds adjust their flight initiation distance to road speed limits

Behavioural responses can help species persist in habitats modified by humans. Roads and traffic greatly affect animals'' mortality not only through habitat structure modifications but also through direct mortality owing to collisions. Although species are known to differ in their sensitivity to the risk of collision, whether individuals can change their behaviour in response to this is still unknown. Here, we tested whether common European birds changed their flight initiation distances (FIDs) in response to vehicles according to road speed limit (a known factor affecting killing rates on roads) and vehicle speed. We found that FID increased with speed limit, although vehicle speed had no effect. This suggests that birds adjust their flight distance to speed limit, which may reduce collision risks and decrease mortality maximizing the time allocated to foraging behaviours. Mobility and territory size are likely to affect an individuals'' ability to respond adaptively to local speed limits.     

Effect of Approaching Boats on Nesting Black Skimmers: Using Response Distances to Establish Protective Buffer Zones

ABSTRACT Understanding how birds respond to the activities of people is an important component of conserving wildlife. We measured responses of nesting black skimmers (Rynchops niger) to an approaching boat in Barnegat Bay, New Jersey, USA, by examining distance to first respond, distance to flush, and time to return to the colony. Our objective was to determine if response distances of skimmers changed as a function of year, reproductive stage, direction of approach (direct or tangential), or number of birds nesting in the colony. Generally, reproductive stage had the greatest effect on all responses, followed by direction of approach, number of adults present at the colony, number of nests, and year, which also explained variation in behavioral responses. The distance at which skimmers first flew when a boat approached decreased from the pre-egg-laying period to hatching, and then increased slightly later in the season. Time (x̄± SE) for skimmers to return to the nesting colony varied seasonally, with birds taking longer to return during the pre-egg period (9.5 ± min) than during hatching (0.7 ± 0.1 min). The decision process for determining set-back distances to protect nesting skimmers should involve selecting 1) behavioral response of highest concern, 2) reproductive stage of highest concern, and 3) an appropriate level of response at which to establish the buffer area. We recommend that managers use a set-back distance of ± 118 m from the perimeter of the colony for black skimmers, which is the 95% percentile of the distance that skimmers first flew in response to approaching boats. Managers can use these data to set buffer distances for skimmers and other colonial birds.     

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].     

Flight initiation distance in Lepidopterans is species-specific and positively related to starting distance

Escape behaviour is a critical component of invertebrate life history but is poorly studied. Flight initiation distance (FID) indexes escape propensity, and is well-studied in vertebrates but is entirely unstudied in Lepidopterans, despite their obvious escape behaviour. Here we test two general principles regarding FID as derived from studies of vertebrates to examine if they apply to Sri Lankan butterflies: 1) that FID is a species-specific trait and 2) that FID increases with Starting Distance, the distance at which the experimenter begins an approach. We collected 295 FIDs from 17 species and find that 1) FIDs are a tractable way of indexing butterfly escape and 2) both the general principles tested apply to butterfly escape. We also present FIDs of these species to encourage further data collection and comparative analysis of butterfly escape.     

The effect of frequency and nature of pedestrian approaches on the behaviour of wandering albatrosses at sub-Antarctic Marion Island

The effects of disturbance frequency, pedestrian group size, history and approach distance were tested through standardised approaches to 148 brooding/guarding wandering albatrosses (Diomedea exulans) at Marion Island in 2006. Seldom-visited birds were approached at different frequencies over a 3-day period and chick survival was monitored 2 weeks later. Two-person approaches were made to some seldom-visited birds and to birds that have recently been bled. Birds close to the station and in a long-term study colony were also approached. non-vocal response (NVR), vocal response (VR) and overall response (OR) of individuals were analysed. Frequency of approach did not influence short-term behavioural responses, but affected chick survival significantly—nests approached most often had the highest proportion of failures. Over the long-term, there was sensitisation to disturbance. Low OR ranks were found for 71.7% of seldom-disturbed birds, 41.7% of study colony birds and 28.6% of birds close to the station. Management regulations at the island are likely to be effective in protecting this species from human disturbance.     

Life on the edge: survival and behavioural responses of freshwater gill‐breathing snails to declining water level and substratum drying

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