Flight initiation distance and refuge in urban birds

Recommendations on How to Use Flight Initiation Distance Data in Birds

Birds and other wildlife are negatively affected by many anthropogenic activities, including human recreational activities, which are often not considered in area planning. Here, I present factors affecting the flight initiation distance (FID)-the distance to an approaching human at which birds flee-for 1075 different flocks of waterbirds. The FID varied greatly between groups of birds and species. For some bird groups and species, the FID was longer in rural areas than in urban areas and increased with flock size and with disturbance from canoeing. In addition to the differences in FID between species and groups of species, there are two important conclusions from this study: (1) a graphical relationship between the proportion of birds that flee at different distances from an approaching person gives more information than mean or median FID values and should be used by nature managers, and (2) the FID should be investigated in each area before mitigating actions or new constructions are decided, considering all the factors affecting it. A global database with a mixture of FID values from a huge number of areas is valuable for some purposes but can be misleading for individuals in a specific area.

Human recreational activity does not influence open cup avian nest survival in urban green spaces

The breeding period of birds is a critical and sensitive portion of the annual cycle. Understanding how human use of urban green spaces affects nest survival can improve our understanding of conserving breeding bird populations in cities and support science-based management of urban green spaces that benefit both people and nature. We conducted a nest survival field study between April and August of 2023 in multiple green spaces in Montreal, Quebec, Canada, the country's second-largest city. We asked whether human presence (distance to trails and amount of human activity) influences the nest survival of four common open-cup nesting bird species: American robins (Turdus migratorius), gray catbirds (Dumetella carolinensis), Northern cardinals (Cardinalis cardinalis), and yellow warblers (Setophaga petechia). We also asked if variables traditionally associated with nest survival, such as vegetation concealment and seasonality, would influence nest survival. Our analyses surprisingly revealed no significant influence of human activity, vegetation concealment, and seasonality on nest survival for our target species. We found for nests that did fail, nests established during the earlier part of the nesting period failed faster. American robin nests were the most successful of our study's four target species, whereas Northern cardinal nests were the least successful. Within the limitations of our study system, our findings suggest that human presence on trails is not negatively impacting the nesting success for our target bird species using urban green spaces. Our study provides integrated science advice to land managers so they can support opportunities for people to connect with nature without causing trade-offs with biodiversity conservation.

Supplementary Information

The online version contains supplementary material available at 10.1007/s11252-024-01669-0.

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.

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.

Nearest neighbour distance does not affect escape behaviour in urban hooded crows

The nearest-neighbour distance is an important property of a group, as individuals can obtain environmental information more quickly and easily from nearby individuals. We examined whether distance to the nearest neighbour affected two components of escape behaviour - alert distance (AD) and flight initiation distance (FID) - in an urban population of hooded crows Corvus cornix, while controlling for confounding variables. We did not find evidence that AD and FID were influenced by the nearest neighbour distance. However, both AD and FID were negatively affected by feeding activity of individuals - focal crows alerted later and escaped at shorter distance if they were feeding during our approach. In addition, AD and FID were positively related to starting distance and grass coverage. The lack of evidence for the nearest neighbour effect on escape behaviour of crows may be due to: (1) disturbance by close neighbours that may impede antipredator behaviour of focal birds, (2) variable distribution of familiar, dominant or experienced individuals within a flock, and (3) dynamic change in position of the nearest neighbour during the potential predator approach.

Impact of tourism on the vigilance behavior of the Cyprus rock agama (Laudakia cypriaca)

Escape behavior is a common antipredator strategy among wild animals. Here, we investigated the effect of four factors on the vigilance behavior of the endemic Cyprus rock agama (Laudakia cypriaca). Flight initiation distance (FID, the minimum distance to which an observer can approach a lizard before it flees) was measured in relation to the type of location (tourist vs. nontourist area), the observer's starting distance, air temperature, and substrate temperature. We collected data for 39 agamas in tourist areas and 34 of these lizards in nontourist areas. As a whole, the mean starting distance was 10.5 m and the FID was 3.6 m. The average substrate temperature was 34.0°C and the average air temperature 29.6°C. Only the type of area affected the agamas' escape decisions with FID being 1.8 m shorter in tourist areas than in nontourist areas (2.7 m vs. 4.5 m). This is probably due to the habituation of lizards to the presence of humans in the former areas. This study shows that tourism strongly affects the behavior of lizards, which may have consequences for the functioning of the population. Tourists can increase the safety of lizards by creating a human shield to deter predators. Once the tourist season is over, lizards may become more vulnerable to predators.

Managing wildlife tolerance to humans for ecosystem goods and services

Many animals can vary their behaviors to better utilize anthropogenic environments. Wildlife living in highly disturbed environments often show an increased tolerance towards humans. While animal behavior can play a vital role in producing and delivering ecosystem services, we know less about how variation in wildlife tolerance to humans can influence ecosystem services. Increased tolerance to humans changes a variety of animal behaviors, and these behavioral modifications, such as changes to foraging, habitat selection, and movement, can alter the supply and flow of both ecosystem services and disservices. We highlight the need to understand the links between increased tolerance to humans and ecosystem services to develop an effective tool to enhance services while minimizing the risk of creating disservices.

Urban birds become less fearful following COVID-19 reopenings

Following the COVID-19 pandemic, many people around the world stayed home, drastically altering human activity in cities. This exceptional moment provided researchers the opportunity to test how urban animals respond to human disturbance, in some cases testing fundamental questions on the mechanistic impact of urban behaviours on animal behaviour. However, at the end of this 'anthropause', human activity returned to cities. How might each of these strong shifts affect wildlife in the short and long term? We focused on fear response, a trait essential to tolerating urban life. We measured flight initiation distance-at both individual and population levels-for an urban bird before, during and after the anthropause to examine if birds experienced longer-term changes after a year and a half of lowered human presence. Dark-eyed juncos did not change fear levels during the anthropause, but they became drastically less fearful afterwards. These surprising and counterintuitive findings, made possible by following the behaviour of individuals over time, has led to a novel understanding that fear response can be driven by plasticity, yet not habituation-like processes. The pandemic-caused changes in human activity have shown that there is great complexity in how humans modify a behavioural trait fundamental to urban tolerance in animals.

Disentangling the "many-eyes", "dilution effect", "selfish herd", and "distracted prey" hypotheses in shaping alert and flight initiation distance in a colonial seabird

Group living is thought to have important antipredator benefits for animals, owing to the mechanisms of shared vigilance ("many-eyes" hypothesis), risk dilution ("dilution effect" hypothesis), and relative safety in the center of the group ("selfish herd" hypothesis). However, it can also incur costs since social stimuli, such as conspecific aggression, may distract individuals from anti-predator behavior ("distracted prey" hypothesis). We simultaneously evaluated how these four different hypotheses shape anti-predator behaviors of breeding king penguins (Aptenodytes patagonicus), which aggregate into large colonies, experience frequent aggressive social interactions, and are regularly exposed to predation by giant petrels (Macronectes sp.) and brown skuas (Catharacta loonbergi) when breeding on land. We approached 200 incubating penguins at four different periods of the breeding season across a range of overall increasing colony densities. We measured the distance at which focal birds detected the approaching threat (alert distance: AD), whether birds decided to flee or not, and the distance of flight initiation (flight initiation distance: FID, viz. the bird attempting to walk away with its egg on its feet). We quantified relative local neighbor density, centrality within the colony (rank), and the number of aggressions the focal bird emitted towards neighbors during the approach. We found that birds engaged in aggressive conflicts with neighbors were less likely to flee, and that increasing relative local neighbor density at low and medium overall colony density resulted in a decrease in bird AD, both supporting the "distracted prey" hypothesis. However, at maximal overall colony density, increasing relative local neighbor density resulted in longer AD, supporting the "many-eyes" hypothesis. We found no support for the "dilution effect" and "selfish herd" hypotheses, and no effects of any hypothesis on FID.

Lockdown effects on fear revealed direct and indirect effects of human presence on perceived predation risk

The Covid-19 lockdown reduced drastically human presence outdoors, providing an uncontrolled experiment for disentangling direct and indirect effects of human presence on animal fearfulness. We measured 18,494 flight initiation distances (FIDs, the distance at which individual animals fly away when approached by a human) from 1333 populations of 202 bird species taken in four European cities both before, during and after the lockdown. FIDs decreased during lockdown in rural habitats but increased in urban habitats, especially for singing birds. Height above ground increases during lockdown in non-singing birds only, and birds adjusted horizontal tolerance to approach according to height outside lockdown, in rural habitats and while not singing. Responses showed lagged effects after lockdown in urban but not in rural habitats. Differential responses to lockdown among habitats and between signing and non-singing birds were consistent with relaxation of direct disturbance effects on birds in rural habitats during lockdown, as well as with increased indirect fear effects mediated by predator release in cities. FIDs seemed to measure the balance of direct and indirect effects of humans on predations risk and food needs rather than direct effects of humans on fear.

Effects of light and noise pollution on avian communities of European cities are correlated with the species' diet

Urbanization affects avian community composition in European cities, increasing biotic homogenization. Anthropic pollution (such as light at night and noise) is among the most important drivers shaping bird use in urban areas, where bird species are mainly attracted by urban greenery. In this study, we collected data on 127 breeding bird species at 1349 point counts distributed along a gradient of urbanization in fourteen different European cities. The main aim was to explore the effects of anthropic pollution and city characteristics, on shaping the avian communities, regarding species' diet composition. The green cover of urban areas increased the number of insectivorous and omnivorous bird species, while slightly decreasing the overall diet heterogeneity of the avian communities. The green heterogeneity-a measure of evenness considering the relative coverage of grass, shrubs and trees-was positively correlated with the richness of granivorous, insectivorous, and omnivorous species, increasing the level of diet heterogeneity in the assemblages. Additionally, the effects of light pollution on avian communities were associated with the species' diet. Overall, light pollution negatively affected insectivorous and omnivorous bird species while not affecting granivorous species. The noise pollution, in contrast, was not significantly associated with changes in species assemblages. Our results offer some tips to urban planners, managers, and ecologists, in the challenge of producing more eco-friendly cities for the future.

Fear in urban landscapes: conspecific flock size drives escape decisions in tropical birds

Human-induced disturbances affect animal behaviours such as anti-predatory responses. Animals in urban environments tend to exhibit a reduced escape response, measured as a shorter flight initiation distance (FID), compared to their rural counterparts. While FID has been evaluated in animals dwelling in contrasting habitats (e.g. urban versus rural), little is known about how this response varies within urban environments, especially in tropical cities. Here, we studied the FID of 15 resident bird species in Bogota, Colombia, at 22 sites grouped into four categories (natural sites, metropolitan parks, zonal parks and residential areas) that differed in landscape features and evaluated which factors affected the escape responses of birds. We showed that birds foraging in larger flocks are more tolerant when being approached but they do not seem to be influenced by other factors such as heterospecific flock size, noise levels, pedestrian density, predator density, natural cover or body length. Also, birds inhabiting residential areas and parks showed a shorter FID compared to birds in natural areas suggesting that they are more tolerant of human-related disturbances compared to their conspecifics that live in natural areas within the city. Our study shows important differences in bird anti-predatory responses within the city and suggests that social strategies (i.e. flocking patterns) may be a mechanism for adapting to human-induced disturbances in urban tropical environments.