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.

Bird tolerance to humans in open tropical ecosystems

“…For instance, such data can be used to help develop set-back zones 20,21 to protect vulnerable species and highlight that annual variation (e.g., during the wet season) might require variable management strategies throughout the year. Our results also support the idea that some patterns of avian tolerance may be general, such as earlier escapes elicited in areas with lower human disturbance and activity 11,12 , earlier escapes initiated by longer approaches 19,23,35 as well as larger (and often threatened) birds being more risk-averse 10,18,22 , whereas other associations may be more geographically, taxonomically or temporally variable 10,23 . To our knowledge, our study represents the first attempt to describe circumtropical variation in avian tolerance towards humans.…”

“…We first selected two proxies for the level of human disturbance at each sampled site, specifically habitat type (rural or urban) and the level of human disturbance (measured as human footprint index which represents cumulative human pressure based on variables such as built-up environments, human population density, or infrastructure density) 12,22 . Then, we collected data on a set of ecological and environmental variables and life-history traits that correlated with avian tolerance towards humans (i.e., flight initiation distance) in previous studies.…”

Heat stress increases risk taking in foraging shorebirds

“…As observations were clustered between early and late October (16 days) and between late January and mid‐April (37 days), we used season (wet versus dry) instead of calendar days in all analyses. We converted local time to minutes after sunrise, as time of day may influence avian FIDs (Ekanayake et al, 2022; Ferguson et al, 2019). We also extracted the predicted time of low tide for the Bijagós (Bubaque) from Instituto Hidrográfico (https://www.hidrografico.pt) to calculate the time before or after low tide—we applied a correction of −35 min to all observations made in Adonga, due to differences in the timing of low tide at this location (Granadeiro et al, 2021).…”

“…As observations were clustered between early and late October (16 days) and between late January and mid-April (37 days), we used season (wet versus dry) instead of calendar days in all analyses. We converted local time to minutes after sunrise, as time of day may influence avian FIDs (Ekanayake et al, 2022;Ferguson et al, 2019). We also extracted the predicted time of low tide for the Bijagós (Bubaque)…”

Animal-friendly behavioral testing in field studies: examples from ground squirrels

“…During repeated trials over a short time period, test subjects can become habituated to human intruders and flee at shorter approach distances ( Petelle et al, 2013 ). Similarly, in areas with high human population density, animals can become acclimated to people and flee at shorter distances during flight tests ( Ekanayake et al, 2022 ). In some cases, influences of human activity on results of flight tests can be applied to understanding human-wildlife coexistence and can provide insights into behavioral responses to environmental changes caused by anthropogenic activity ( Pettit et al, 2021 ; Mikula et al, 2023 ).…”