Differences in flight initiation distances between African and Australian birds

Estimating setback distances for a threatened, cryptic, data-sparse migratory shorebird

Cryptic fauna species using highly modified habitats face many conservation challenges, with disturbance from human use being an ongoing issue across many global settings. Setbacks or buffers are a key planning tool for protecting habitat, and are often specified under law. However, for many species using modified and urban habitats there are no published data on how wide setbacks should be. Latham's Snipe (Gallinago hardwickii) is a case in point. It is a threatened, cryptic, migratory shorebird that breeds in Japan and spends its non-breeding season almost entirely in Australian wetlands and grasslands. Many sites used by snipe are within urban areas, potentially triggering protections under national law and there is an urgent need for information on setbacks to inform planning and conservation management. The aim of this project was to derive transparent, scientifically-derived buffer recommendations for mitigating disturbance to Latham's Snipe, by estimating Alert Distances (AD; the first sign of behavioural disruption associated with human proximity) from measures of flush distances (FIDs; the distance at which flight occurs). ADs are almost impossible to observe in this cryptic species which uses dense habitat. We used 1529 FIDs to estimate AD from: (1) a within-species regression of FID against the few available ADs for this species (n =  8), and (2) cross-species associations between AD and FID of Scolopacidae from analysis of an unpublished dataset. FIDs varied between site and observers, so we resampled using bootstrapping to account for this variation and produce estimates of AD. Based on these estimates, we recommend minimum buffer widths between 75 - 110 m, which would prevent 80 - 95% of vigilance responses by Latham's Snipe, respectively. The methods we employ may be useful in determining appropriate buffer widths for other cryptic fauna species. These buffers should be monitored for effectiveness and adapted as required.

Lifting the Veil of Darkness: Thermal Technology Facilitates Collection of Flight-Initiation Distances by Night

Flight-Initiation Distance (FID)-a direct measure of an individual animal's escape response-is a widely used method to study escape ecology in fauna. The technique has primarily been applied to bird species that are active by day. Indexing the escape behaviour of nocturnal species has been limited due to the need for light to detect and observe animals which confounds behavioural responses. We demonstrate the use of existing high-end thermal technology to facilitate standardised, un-biased, nocturnal FIDs in small and large, terrestrial and arboreal animals, which feature initial separation (starting) distances which are the same by day and night. We provide the following (1) method for collecting FIDs by night which specifically addresses solutions to novel challenges associated with collecting these by night, (2) report of the FIDs of some strictly nocturnal bird and mammal species and compare diurnal and nocturnal FIDs for some species, (3) demonstration that the positive daytime relationship between FID and Starting Distance also occurs by night, and (4) minimum sample size threshold for quantifying escape responses and how these vary when sampling the FIDs of different animal species by night. We demonstrate the capacity to conduct nocturnal FIDs on a broad range of taxa not previously studied. We recommend 25-50 samples are needed to accurately quantify a species escape response in a particular context. Our method expands the capacity to understand how species escape by night, a critical period during which many predator-prey interactions occur.

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.

Responses of birds to observers holding popguns: Hunting history influences escape behavior of urban birds

Human activities affect bird behavior both directly and indirectly. Birds constantly regulate their behavior in response to human disturbance. Gun hunting, a major directional disturbance, puts enormous selection pressure on birds. In China, gun bans have been in place for nearly 30 years, and little hunting using guns occurs in modern cities. However, little attention has been paid to whether a history of hunting still affects the behavioral adaptations of urban birds. In this study, we compared the flight initiation distance (FID) of the Eurasian tree sparrow Passer montanus, Azure-winged magpie Cyanopica cyanus, Common hoopoe Upupa epops and Eurasian magpie Pica pica in the presence of observers with or without popguns. The Eurasian tree sparrow, Azure-winged magpie, and Eurasian magpie effectively recognized the difference between the observers, and perceived the armed observer as a greater threat, exhibiting earlier escape behavior, but this phenomenon was not found in the Common hoopoe. The different expressions in FID of experimental bird species in China cities may be affected by the different levels of recognition of hunting pressure due to different hunting histories.

Bird tolerance to humans in open tropical ecosystems

Animal tolerance towards humans can be a key factor facilitating wildlife-human coexistence, yet traits predicting its direction and magnitude across tropical animals are poorly known. Using 10,249 observations for 842 bird species inhabiting open tropical ecosystems in Africa, South America, and Australia, we find that avian tolerance towards humans was lower (i.e., escape distance was longer) in rural rather than urban populations and in populations exposed to lower human disturbance (measured as human footprint index). In addition, larger species and species with larger clutches and enhanced flight ability are less tolerant to human approaches and escape distances increase when birds were approached during the wet season compared to the dry season and from longer starting distances. Identification of key factors affecting animal tolerance towards humans across large spatial and taxonomic scales may help us to better understand and predict the patterns of species distributions in the Anthropocene.

The habitat connectivity hypothesis of escape in urban woodland birds

Habitat destruction and fragmentation increasingly bring humans into close proximity with wildlife, particularly in urban contexts. Animals respond to humans using nuanced anti-predator responses, especially escape, with responses influenced by behavioral and life history traits, the nature of the risk, and aspects of the surrounding environment. Although many studies examine associations between broad-scale habitat characteristics (i.e., habitat type) and escape response, few investigate the influence of fine-scale aspects of the local habitat within which escape occurs. We test the "habitat connectivity hypothesis," suggesting that given the higher cost of escape within less connected habitats (due to the lack of protective cover), woodland birds should delay escape (tolerate more risk) than when in more connected habitat. We analyze flight-initiation distances (FIDs) of five species of woodland birds in urban Melbourne, south-eastern Australia. A negative effect of habitat connectivity (the proportion of the escape route with shrubs/trees/perchable infrastructure) on distance fled was evident for all study species, suggesting a higher cost of escape associated with lower connectivity. FID did not vary with connectivity at the location at which escape was initiated (four species), apart from a positive effect of habitat connectivity on FID for Noisy Miner Manorina melanocephala. We provide some support for two predictions of the "habitat connectivity hypothesis" in at least some taxa, and conclude it warrants further investigation across a broader range of taxa inhabiting contrasting landscapes. Increasing habitat connectivity within urban landscapes may reduce escape stress experienced by urban birds.

Susceptibility to Predation Varies with Body Mass, Foraging Niche, and Anti-Predator Responses among Bird Species

Predation is a major source of mortality for many avian species. Species that face more predators, and those with less effective anti-predator responses, are presumably more likely to die from predation over time. Predation rate, as a measure of susceptibility to predation, is difficult to measure in the field. Radio-tracking studies, however, allow researchers to determine the time and cause of death of marked individuals, making it possible to estimate predation rate. I used estimates of predation rates from a large number of published radio-tracking studies in birds to assess in a phylogenetic framework the effect of several potential determinants. I obtained 393 estimates of predation rates from 129 species. Predation rates were lower in areas with fewer predators, such as islands and aquatic habitats, and for species with fewer potential predators, such as larger species. The predation rate was also lower for prey species with effective anti-predator responses, such as those that forage in flocks. Radio-tracking studies provide a unique opportunity to estimate overall predation rate in the field. Broadening the range of species and the range of habitats involved in such studies will help to further elucidate the factors that affect susceptibility to predation.

Ecological and environmental predictors of escape among birds on a large tropical island

Abstract

Ecological and environmental traits can influence avian escape behaviour but most data underpinning our current understanding relates to continental and temperate areas and species. We conducted a phylogenetically controlled comparative analysis of flight-initiation distance (FID) against a variety of environmental, behavioural and life history attributes for Sri Lankan birds (202 species; n = 2540). As with other studies, body mass was positively associated with FID, and longer FIDs occurred in areas where human population density was lower. We also found that the effect of human population density was more pronounced in larger birds. Birds that were in groups when approached tended to have longer FIDs. Unlike the findings of other comparative analyses, based mostly on continental, temperate populations, most other ecological variables did not feature in the best models predicting FID (time of year, breeding system, clutch size, habitat, migratory behaviour, development [altricial/precocial], elevation and diet). Thus, some associations (body mass and exposure to humans) may be universal, while others may not manifest themselves among tropical avifaunas. Further tropical datasets are required to confirm truly universal associations of environmental and ecological attributes and escape distances among birds.

Significance statement

Escape responses in birds are influenced by the environment in which they live, the conditions under which they face a threat and their own biological characteristics. The vast majority of our knowledge of avian escape behaviour is derived from continental, temperate species. We examined the environmental and ecological factors that shape flight-initiation distance (FID), the distance at which a bird reacts to an approaching threat (a walking human) by escaping, using 2540 observations of 202 bird species on a large tropical island—Sri Lanka. Several predictors of FIDs in birds are clearly influential for Sri Lankan birds: body mass, human population density and whether the bird is alone or in as group. However, many other putative predictors are not, suggesting that tropical island avifaunas may have different responses to approaching threats compared to their temperate continental counterparts.