Initial Distance Research Articles

Social Security: Individuals in Socially Reciprocal Groups May Perceive Security from Predators

Abstract One of the most explored factors mediating antipredator behavior is group size, which generally predicts individuals in larger social groups allocate less time to antipredator vigilance while foraging. However, group size alone does not capture the full complexity of sociality. An individual’s ‘sense of security’, or their perceived risk of predation, is also influenced by an individual’s social connections. Further, group social structure – the pattern of all social interactions in a group – could explain additional variation in perceptions of security for the individuals that reside in the group. Using the time allocated to vigilance during foraging and flight initiation distance (FID) to quantify individuals’ social security, we explored whether individual yellow-bellied marmots (Marmota flaviventer) in tightly connected social groups looked less while foraging and had shorter FIDs. Using linear mixed effect models, we found modest support for the Social Security Hypothesis; individuals in more socially reciprocal groups may spend less time looking for predators while foraging. No measure of group social structure explained variation in FID. Measures of the immediate environment (the number of individuals within 10 meters for vigilance and the distance from burrow and alert distance for FID) had effect sizes an order of magnitude greater than measures of social structure, suggesting an individual’s immediate environment has more of an impact on their antipredator behavior than the structure of their social group.

Weak evidence for a relationship between group size and flight initiation distance in response to underwater human presence in an exploited fish species

Group size can influence flight initiation distance (FID), a key antipredator behavior, in many animal species. In fishes, however, the effect of group size on FID remains unclear. Two different mechanisms might explain a putative relationship between group size and FID. If fish benefited from having more vigilant individuals around, we would expect group size to be positively associated with FID (considering collective vigilance in the context of the many eyes hypothesis). By contrast, if fish benefited from a predator dilution effect, we would expect group size to be negatively associated with FID. Importantly, such relationships should be critically sensitive to background risk levels. We capitalized on FID observations inside and outside marine protected areas and simulated risk by having a risky spearfisher or a non-risky snorkeler swim towards white seabream (Diplodus sargus) to estimate the relationship between FID and group size. Model selection provides weak evidence that group size positively influences FID of white seabream when group size was modelled two ways: categorically (alone vs. shoal), and continuously (range 2–15). While the results suggest that overall group size has a measurable impact on FID, the presence of spearfishers or snorkelers had a weak effect on the relationship of group size and FID, which seems to be more sensitive exclusively to the protection level (inside/outside marine protected areas). Our findings align with previous studies showing mixed results on the relationship between group size and FID. This study underscores the complexity of antipredator behaviors in natural settings and suggests that multiple interlinked factors, rather than group size alone, drive FID in fishes. Future research should integrate field observations, laboratory experiments, and modeling to study the ecological influence of group size on FID more comprehensively.

Do Oystercatchers hate drones? A comparison of flight initiation distances of four wader species in response to drone intrusion

Do Oystercatchers hate drones? A comparison of flight initiation distances of four wader species in response to drone intrusion

Declarative ship arenas under favourable conditions

According to maritime regulations, a collision-avoidance action shall be taken at an “ample time” while strict interpretation of this term is ambiguous. Evasive manoeuvres, executed by marine navigators on a daily basis, are usually carried out well in advance, while the distance at which they decide to perform such a manoeuvre is mostly subjective and results, e.g., from the navigator's seagoing experience. A proper understanding of the decision-maker's behaviour under favourable conditions, when time pressure does not exist, seems to be essential for the future of maritime safety. This could enable the translation and quantification of seafarers' routine actions, taken many times a day, into collision-avoidance algorithms suitable for Decision Support Systems (DSS) or Maritime Autonomous Surface Ships (MASS). The literature lacks extensive research on this subject, as it focuses mainly on safety-critical actions, which are important but rare events. Therefore, this study aims to fill this gap by surveying practitioners and extracting their expert knowledge. Based on an online survey, the declarative ship arenas, reflecting the distance of evasive manoeuvre initiation, were determined and analysed. The findings revealed that, depending on the participants' profiles, a range of responses among the groups reaches up to 2 NM. The results indicated that navigators become less consistent with growing experience. Determined declarative arenas were consequently incorporated into a simulation-based case study of a passenger ship. The conducted simulations indicated that for several scenarios, the passing distances resulting from the execution of an evasive manoeuvre as per declarative arena were less than 0.5 NM, potentially leading to dangerous situations at close range. This results most likely from an overall problem of translating the distance of manoeuvre initiation into the final passing distance. The findings of this research may be found interesting by shipping companies preparing bridge procedures or for scholars and industry representatives preparing intelligent collision-avoidance solutions for maritime transportation.

Feedback on Escape Behavior of Birds Under Different Hunger Pressure.

The risk of predation has always been a significant impact on wild birds. Birds, facing with limited energy, must balance their investment between foraging and vigilance. There were currently limited understandings of the vigilant behavior feedback of birds under different hunger pressure. Therefore, we employed the White-browed laughingthrush (Pterorhinus sannio) and White wagtail (Motacilla alba) as research subjects to carry out experiments in winter, in exploring the tolerance of birds to external stress under different hunger pressure. After a night of energy expenditure, individuals of both species faced greater hunger pressure in the morning. The results of general linear models showed that the flight initiation distance (FID) of both species in the morning (7:00-9:00) was significantly shorter than that in the evening (16:00-18:00). Additionally, when the weather was cold (daily minimum temperature ≤ 5°C), the FID of the White-browed laughingthrush and White wagtail was significantly shorter in the morning, as same as the results of general linear models. However, when the weather was warm (daily minimum temperature ≥ 10°C), there was no significant difference even though the FID average of both species was shorter in the morning than in the evening. These suggested that the consumption and supplementation of energy are very important for birds, as the higher their hunger pressure, the greater their willingness to forage and take on risk, especially in cold winter.

Flight initiation distance is repeatable and geographically flexible in greylag geese Anser anser

The decision to flee from an approaching threat represents a trade‐off between the costs and benefits of flight. In research to date, particular interest has been given to the effects of urbanisation on predator escape behaviour. However, these differences are most often studied at the population rather than individual level, which makes it difficult to disentangle whether site‐specific differences in predator avoidance are due to behavioural plasticity or non‐random distribution of behavioural phenotypes. In this study, we measured flight initiation distances – a widely used proxy for fearfulness or boldness – in a free‐roaming, human‐habituated, and colour‐banded population of greylag geese Anser anser. First, we tested whether individuals flexibly adjusted their flight initiation distance based on environmental context by approaching the same individuals at two sites with different levels of human presence. Second, we examined whether flock members show consistent differences in their flight initiation distance towards unfamiliar humans. Our results suggest that greylag geese can adjust their behaviour based on environmental context and show individual differences in flight initiation distance that are consistent both within and across years. When individuals regularly move between foraging sites, establishing site‐specific responses to potential threats may allow them to optimise their escape response and thereby avoid unnecessary energetic and opportunity costs.Keywords: Anser anser, behavioural plasticity, boldness, escape behaviour, flight initiation distance

Do agricultural practices on meadows reduce or increase flight initiation distance in the white stork ciconia ciconia?

Do agricultural practices on meadows reduce or increase flight initiation distance in the white stork ciconia ciconia?

Flame acceleration and detonation initiation in a non-uniform hydrogen–air mixture with a combination of fluid and solid obstacles

Flame acceleration and the deflagration-to-detonation transition (DDT) process in premixed combustible gases are complex phenomena involving both fluid dynamics and chemical reactions. However in practical scenarios, premixed combustible gases are often non-uniform. Based on the OpenFOAM platform, this numerical study examines the impact of combined fluid and solid obstacles on flame acceleration and DDT within various non-uniform concentration fields. The results indicate that in the initial stage of flame development, the absence of blockages on one side of the pipe and the presence of a higher concentration of hydrogen contribute to faster flame acceleration. Additionally, the narrow channel formed between obstacles and the wall, enhanced by the pressure gradient, produces a stronger suction effect, causing the flame to experience multiple zones of velocity enhancement. Furthermore, the detonation initiation can be categorized into two types: a) detonation initiated by the interaction between the flame surface and the reflected shock wave; b) detonation triggered by the coupling of the flame front with high-pressure regions. During the detonation wave's propagation, hydrogen levels below 12.7% cause detonation wave decoupling, affecting its shape based on hydrogen concentration distribution. From the perspective of flame evolution, fluid obstacles introduce more disturbances and vortices, promoting the formation of pressure gradients, which accelerates flame development and facilitates detonation initiation. The combination of fluid and solid obstacles can effectively reduce the initiation distance and time required for DDT. Also, a more uniform distribution of hydrogen concentration leads to faster changes in the flame state, enabling quicker detonation initiation.

Inconsistent scientific methods hamper the management of drone use near birds

AbstractDrone use has increased in the last decade, prompting efforts to manage their operation near wildlife. These efforts are hampered by variations in methods among studies, leading to evidence that is fragmented, inconsistent, and incomplete. To address this, we extracted evidence from 194 studies involving drones and birds, covering 314 species, including 61 studies on drone‐induced bird disturbance that encompassed 206 species. We summarized the results of these 61 studies, identified evidence gaps, and developed a standard method for characterizing drone‐induced bird disturbance. Drone‐induced bird disturbance varied with species, breeding status, and distance of the drone from the birds. Key evidence gaps include a lack of studies on small terrestrial species likely to occur in urban environments where drones are often used and limited research in Africa, Asia, and South America. Methods were inconsistent among studies, with only 20% of studies reporting the often‐recommended response variable of flight initiation distance (FID). We conclude that 1) managers should use evidence, including our database, to inform regulations, such as buffer distances, that account for species, breeding status, and drone type, 2) researchers should target contexts where interactions between drones and birds are likely but few studies exist, such as urban environments, and 3) researchers investigating drone‐induced bird disturbance should conduct horizontal and vertical approaches directly towards birds, and record the FID along with predictors describing the environment, target, and stimulus.

Flight initiation distance differs among eumelanin‐based color morphs in feral pigeons

AbstractOrganisms facing anthropogenic activities usually exhibit phenotypic responses assumed to enhance coping with disturbance. These responses include a decreasing degree of reaction toward potentially risky situations (“behavioral tolerance”) with increasing disturbance. Though melanin is associated with many phenotypic traits, including pigmentation and behavior, the potential relationship between behavioral tolerance and melanin has never been explored. Such relationship may potentially result from either direct association between melanin and behavior (e.g., genetic correlation) or indirectly through a coloration‐dependent behavior‐modulating factor (e.g., differential predation or human preferences in cities toward color morphs). Feral pigeons (Columba livia) represent an ideal biological system to test for these hypotheses, due to their presence in cities worldwide, their considerable variation in eumelanin‐based coloration, ranging from white to black plumage, and their close proximity to humans. We measured Flight Initiation Distance (FID, classically used for behavioral tolerance assessment) of feral pigeons of 4 different eumelanin‐based color morphs in sites differing in their urbanization rate and pedestrian traffic within the restricted scale of a city center (Paris). Urbanization rate and pedestrian traffic had no effect on FID, maybe because of the small spatial scale considered. FID varied with eumelanin‐based coloration: white pigeons had lower FID (104.6 cm; i.e., higher behavioral tolerance) than darker morphs (232.3 cm for Blue bar, 184.4 cm for T‐pattern & Checker, and 181.8 cm for Spread color morphs). Though the exact underlying causes remain to be identified, we propose different possible mechanisms for this relationship that remain to be investigated in future work.

Escape behavior of rocky‐reef fish reveals the impact of spearfishing across different management regimes

AbstractFlight initiation distance (FID), the distance at which an organism begins to flee from an approaching threat, is a major component of antipredator escape behavior and a potential indicator of threat perception in fishes. In this study, we analyzed the FID of three important rocky‐reef fish species targeted by spearfishers, which are of commercial and recreational importance. We tested predictions that FID to a diver threat increases with the following factors: (1) fish body size, (2) less restricted access regimes, and (3) increased historical fishing pressure. We studied three size ranges of three rocky‐reef fish species, in three different access regimes (i.e., open access, territorial user rights for fishery areas, no‐take marine protected areas), and in two regions (northern and central region with different levels of fishing pressure depending on the species). We conducted an ANOVA to analyze pairwise interactions. We used the mean square criterion to select the models that best explained the variation of our response variable. Our findings indicate that FID can be distinctly elucidated by factors such as individual size, species, access regimes, and regions. Additionally, our models show that interactions involving regions and either species or size further contribute to explain FID variability. FID was higher in larger fishes and those of higher commercial value, outside marine reserves and in the region with the highest historical fishing pressures (based on landings data). This study supports the predictions that increased FID is associated with the threat posed by spearfishing activities. Furthermore, our findings indicate that spearfishing may already be altering the behavior of rocky‐reef fishes on the north‐central coast of Chile.

Advancing the understanding of spearfisher‐fish behavioural interactions and its management implications

Abstract Fish behaviour is intimately linked to fishing catchability. Measurements of fish behaviour may provide quantitative indicators that inform about the impact of fishing pressure and help design effective management strategies. The implications of spearfishing pressure on fish behaviour have mainly been characterized using single quantitative indicators such as flight initiation distance (FID), which provide incomplete views of spearfisher‐fish behavioural interactions. We used an integrative approach to advance the understanding of spearfisher‐fish behavioural interactions by complementing FID estimates with post‐flight responses (i.e. individual fish behaviour after fleeing), and the decreasing probability to catch a fish at increasing distance from a speargun. We first collected empirical observations of white seabream (Diplodus sargus) FID and post‐flight behaviour in response to an approaching human (spearfisher or snorkeler) inside and outside marine protected areas. We then combined these observations with simulations based on an innovative model representing how catchability changes during a spearfisher‐fish behavioural interaction. Empirical results showed that the likelihood of a still‐vulnerable post‐flight response after fleeing was inversely related to increasing exposure to spearfishers. This demonstrates that post‐flight response can be used as an indicator of spearfishing pressure. Moreover, post‐flight responses provided complementary information to that provided by FID, suggesting that these two indicators should be integrated for a holistic view of spearfishing‐fish interactions, such as in the model and simulations presented here. The simulations demonstrated that: (i) accounting for post‐flight responses may increase likelihood of approach by spearfisher within speargun range by up to 20%; and (ii) accounting for post‐flight responses and decreasing probability of capture with increasing distance from speargun drastically reduces estimates of likelihood of capture of white seabream at minimum catch length limit outside marine protected areas compared with using FID as single indicator of catchability. Synthesis and applications. First, integrating flight initiation distance (FID) measurement with post‐flight responses provides a more realistic indicator to measure fish behavioural reaction to spearfishing pressure. Second, the model presented here showed that spearfishing mortality may drastically decrease when accounting for both prey behaviour (i.e. FID and post‐flight responses) and spearfishers effectiveness (i.e. probability to catch a fish at increasing distance from a speargun). This must be considered to understand population dynamics and potential changes in catchability when spearfishing is managed through temporal restrictions (e.g. seasonal or periodic closures).

Flight initiation distance and bird tolerance to humans in rural and urban habitats.

Urbanization induces homogenization and changes the behavioural patterns of various bird species, thereby facilitating coexistence and prompting adaptations to disturbances in urban environments. However, there is limited research on the influence of how urbanization affects bird tolerance towards humans, especially in developing sub-tropical regions such as Nepal, which is undergoing rapid unplanned urbanization. This study identified the flight initiation distance (FID) as a proxy for assessing bird tolerance. We focused on evaluating the human tolerance levels of 33 bird species using their FIDs in urban and rural habitats within Kathmandu Valley, a rapidly urbanizing city in South Asia. We found higher tolerance in urban birds than in their rural conspecifics, which varies mainly with dietary guild and season. The positive impact on FID was associated with time of the day and body size, while a negative association was observed with flock size, mean population density of humans and interaction between body size and elevation. Our study highlights the increased tolerance level of birds in urban areas, probably owing to habituation, and emphasizes the imperative need to investigate the potential adverse effect on urban bird population owing to this increased tolerance level.

Climatic variation and risk assessment in a highly seasonal mammal

Abstract Climate change and its resulting effects on seasonality are known to alter a variety of animal behaviors including those related to foraging, phenology, and migration. While many studies focus on the impacts of phenological changes on physiology or fitness enhancing behaviors, fewer have investigated the relationship between variation in weather and phenology on risk assessment. Fleeing from predators is an economic decision that incurs costs and benefits. As environmental conditions change, animals may face additional stressors that affect their decision to flee and influence their ability to effectively assess risk. Flight initiation distance (FID)–the distance at which animals move away from threats–is often used to study risk assessment. FID varies due to both internal and external biotic and physical factors as well as anthropogenic activities. We asked whether variation in weather and phenology is associated with risk-taking in a population of yellow-bellied marmots (Marmota flaviventer). As the air temperature increased marmots tolerated closer approaches, suggesting that they either perceived less risk or that their response to a threat was thermally compromised. The effect of temperature was relatively small and was largely dependent upon having a larger range in the full data set that permitted us to detect it. We found no effects of either the date that snow disappeared or July precipitation on marmot FID. As global temperatures continue to rise, rainfall varies more and drought becomes more common, understanding climate-related changes in how animals assess risk should be used to inform population viability models.

Discomfort in pedestrian-electric scooter interactions during frontal approaches

BackgroundAs urban landscapes rapidly integrate e-scooters into their transportation ecosystems, understanding pedestrian-e-scooter interactions becomes paramount for safety and planning. This study investigates pedestrian discomfort levels and avoidance strategies when encountering an e-scooter approaching from the front. Methods25 participants were exposed to e-scooters approaching at three different speeds and lateral distances. Avoidance paths were plotted, and subjective discomfort levels were recorded and analysed. ResultsOur findings underscored two key behaviours: 1) As the speed of the e-scooter increased, participants initiated avoidance manoeuvres from a further distance ahead, suggesting a heightened perception of risk. 2) Regardless of the e-scooter's speed, the lateral distance maintained during passing remained fairly constant. However, when the e-scooter's initial lateral position was closer to participants, both the initiation distance for avoidance and the reported discomfort level increased noticeably. ConclusionThe findings underscore the critical influence of lateral distance and e-scooter speed on pedestrian comfort and avoidance behaviour. These insights can guide urban planners and policymakers in designing safer and more efficient shared spaces.

Predation risk for hoary marmots in Washington’s North Cascades Mountains

Abstract Declines in populations of small mammals associated with high elevations, e.g., marmots (Marmota spp.) and pikas (Ochotona spp.), have been attributed to both direct and indirect effects of environmental changes caused by humans. For example, populations of Olympic marmots (M. olympus) and Vancouver Island marmots (M. vancouverensis) have declined in response to increased predator access to high-elevation marmot habitats. In the North Cascades National Park Service Complex (NOCA), observed mean abundance of hoary marmots (M. caligata) declined by 74% from 2007 to 2016. Although these declines have been linked to harsh winter conditions, the role of predation and its association with decreasing snowpack has yet to be explored in this system. We noninvasively examined these predator–prey dynamics by coupling behavioral surveys of hoary marmots with indices of predation risk. We conducted 145 vigilance samples and 39 flight initiation distance trials to measure Hoary Marmot antipredator behavior. We derived a risk index for each predator by weighting its probability of use estimates (the probability of a predator–prey encounter) with its observed proportion of Hoary Marmot predation (probability of prey death given an encounter). We used genetic metabarcoding of vertebrate DNA from 413 predator scat samples to quantify predation on hoary marmots. We surveyed 9,930 trap-nights using 130 remote cameras to model predator probability of use near Hoary Marmot colonies. From camera traps and scat DNA, we detected 10 predator species in the study area, and we detected hoary marmots in the scats of 5 of these species. The proportion of observed Hoary Marmot predation was highest for coyotes (Canis latrans) at 50%. To our knowledge, we also report the first record of hoary marmots being consumed by Pacific martens (Martes caurina), which were also significant predators (proportion of observed predation = 32%). We expected predators with low-elevation habits to use sites with lesser snow persistence; this prediction was supported for coyotes but not for other typically low-elevation predators. We found estimated risk experienced by hoary marmots was highest from Pacific martens and lowest from Canada Lynx (Lynx canadensis). Contrary to our predictions and despite hoary marmots allocating >50% of their time to vigilance, neither estimates of predator risk nor human presence explained variation in marmot antipredator behavior. Based on the results from both our dietary and probability of use analyses, we expect coyotes to have an increasing effect on NOCA’s Hoary Marmot population as the climate warms and Coyote range continues to expand. Thus, our work highlights the need to better understand the effect of climate-driven shifts in predator–prey ecology in high-elevation systems.

Alert and Flight Initiation Distances of the Coot in Response to Drones

Alert and flight initiation distances are important elements of bird behavioral responses and indicators of their adaptation to external disturbances; therefore, they provide an important basis for bird conservation. With continual rapid advancements in drone technology, the use of drones in bird field surveys is becoming increasingly important. However, the disturbance impact of drones on birds remains controversial and needs further assessment. This study measured the distances at which coots (Fulica atra) tolerated drones in the Baiyangdian wetland, Northern China, over 42 days from August to November 2023 and at the end of July 2024. The results show the maximum alert distance (AD) and maximum flight initiation distance (FID) of the coot to be 44 m and 35 m, respectively. The coots showed no signs of disturbance when the drones flew at an altitude of 50 m. The AD of the coot showed a significant relationship with whether it saw the drones in advance, environmental conditions, and the drone’s behavior before it approached, whereas the FID was only significantly affected by whether the coot saw the drones in advance. The sight of drones in advance considerably increased the AD and FID.

Adaptation of farmland mammalian specialist to urban life: Escape behavior of European hare along the urban-rural gradient

The European hare Lepus europaeus is an iconic but rapidly declining farmland specialist with recently confirmed populations in urban areas. However, their behavioral responses and adaptability to urbanization and life in human-dominated areas are fully unexplored. Here, using infrared cameras, we explored escape behavior (measured as the flight initiation distance) using 965 hare observations in urban and farmland areas in the Czech Republic and Austria (Central Europe) and its association with habitat type, distance to the city center, patch size, season, hare age and initial behavior. We found that European hares adjusted their escape behavior to habitat type and escaped significantly earlier in farmland (rural) habitats than in urban habitats. However, escape distances of hares did not differ between farmland types with different degree of habitat heterogeneity. We also revealed that urban hares escaped earlier when located further from the city center or in a larger study patch. Moreover, adult hares escaped earlier than subadults and foraging individuals escaped earlier than resting hares but both only in rural areas. Our results support high behavioral adaptability of European hares to human-dominated urban areas.

Do risk-prone behaviours compromise reproduction and increase vulnerability of fish aggregations exposed to fishing?

Human disturbances can prompt natural anti-predator behaviours in animals, affecting how energy is traded off between immediate survival and reproduction. In our study of male squaretail groupers (Plectropomus areolatus) in India's Lakshadweep archipelago, we investigated the impact of fishing pressure on anti-predatory responses and reproductive behaviours by comparing a fished and unfished spawning aggregation site and tracking responses over time at the fished site. Using observational sampling and predator exposure experiments, we analysed fear responses (flight initiation distance, return time), as well as time spent in vigilance, courtship and territorial defence. Unpaired males at fished sites were twice as likely to flee from simulated predators and took longer to return to mating territories. In contrast, paired males at both sites took greater risks during courtship, fleeing later than unpaired males, but returned earlier at the unfished site compared with the fished site. Our findings suggest that high fishing pressure reduces reproductive opportunities by increasing vigilance and compromising territorial defence, potentially affecting mate selection cues. Altered behavioural trade-offs may mitigate short-term capture risk but endanger long-term population survival through altered reproductive investment. Human extractive practices targeting animal reproductive aggregations can have disruptive effects beyond direct removal, influencing animal behaviours crucial for population survival.

Tourism influences escape behavior of lizards in relationship with human clothing color

Increased tourism pressure modifies animal behavior, including alterations in anti-predator responses and foraging activity. In areas with high tourist presence, animals may become accustomed to increased human activity and adjust the intensity of some defensive responses. An animal’s anti-predation ability is usually estimated by measuring its Alert Initiation Distance (AID) and Flight Initiation Distance (FID). Both indexes are affected by multiple factors including the color of the observer’s clothing. Animal behavior is also influenced by human presence, and individuals may become accustomed to increased human presence, e.g. in tourist areas. In this study, we analysed the escape behavior of the endemic Cyprus rock agama (Laudakia cypriaca) in relation to the observers clothing color. Our results showed that AIDs and FIDs of agamas in tourist areas were significantly shorter than those in non-tourist areas. Moreover, in non-tourist areas, AIDs and FIDs of agamas were significantly longer when the observer wore red clothes, compared to green and grey clothes. Our results may be helpful in planning research taking into account various colored clothing based on expected reptilian reactions. Furthermore, our results may determine the proximity at which humans interact with animals, considering clothing color, to prevent negative impacts especially on rare and protected lizard species.