Level of local human disturbance and feeding state determines escape behaviour in Eurasian Oystercatchers

Abstract

Human disturbances may constitute a significant stressor for wildlife, especially where human recreational activities overlap with fitness‐enhancing activities such as feeding. Disturbances cause an animal to flee from the perceived predation risk, using energy, rather than remaining and gaining energy. Such reactions are, however, context‐dependent, as predicted by optimal escape theory: animals should only flee when the perceived risk of predation of remaining exceeds the risk of starvation of leaving. Animals may also learn that humans do not generally represent a predation risk after repeated false alarms and then learn to only respond when approached deliberately and closely. We tested the Flight Initiation Distance (FID; distance at which an approached animal begins escape) of feeding or roosting Eurasian Oystercatchers Haematopus ostralegus (oystercatchers) to a human (as a simulated predator) in areas with or without humans on beaches in south‐east Scotland. We predicted roosting oystercatchers to respond earlier (greater FID) than feeding birds because the risk of starvation will be lower, and earlier on beaches where there were no humans at the start of the experiment because a human will then represent a more novel predator signal. As predicted, oystercatchers escaped at greater distances away from the perceived threat when feeding and in areas with humans. We found that escape distances decreased (greater tolerance of the perceived threat) as the number of people in an area increased, but people being present or not explained more of the variation in the data. The results show that oystercatchers habituate on a short timescale to non‐lethal human presence and generally respond to perceived predation risk in accordance with the predictions of optimal escape theory.

Heat stress increases risk taking in foraging shorebirds

“…Our finding that FIDs were shorter in areas where human presence is frequent compared with areas virtually undisturbed by humans may reflect some level of habituation to frequent exposure to non-lethal human activities (Azaki & Cresswell, 2021;Mikula, 2014).…”

“…Our finding that FIDs were shorter in areas where human presence is frequent compared with areas virtually undisturbed by humans may reflect some level of habituation to frequent exposure to non‐lethal human activities (Azaki & Cresswell, 2021; Mikula, 2014). Individuals using areas with regular human presence could be selected to adapt by making short‐term behavioural responses to disturbance (e.g.…”

“…Yet, the low macroinvertebrate biomass suggests limited food availability for shorebird communities in these intertidal areas (Lourenço et al, 2018). This finding also suggests that tidal rhythms, rather than circadian ones, modulate the escape behaviour of coastal shorebirds (Azaki & Cresswell, 2021). Further study is required to investigate the interactions between tidal and daily cycles in the risk taking and foraging of shorebirds across different landscapes of fear.…”

“…(3) Birds feeding at sites with regular human presence increase tolerance of human proximity due to habituation or tolerance to non‐lethal human presence effects (Blumstein, 2013). Specifically, we predicted that foraging birds would respond earlier (longer FIDs) on intertidal flats where human presence is virtually null because a human will then represent a more novel predator signal (Azaki & Cresswell, 2021; Mikula, 2014) (Figure 2d). We tested these predictions while controlling for phylogeny and other variables that can influence escape responses (Figure 2e,f).…”

Opposing effects of vigilance and foraging on escape behaviour in hooded crows

“…Thus, Bonaire whiptail lizards (Cnemidophorus murinus) escaped at shorter distances in trials in which food was supplied . Similarly, wild hyraxes (Heterohyrax brucei and Procavia capensis) and oystercatchers (Haematopus ostralegus) exhibited shorter FID when feeding than resting or being vigilant (Mbise et al, 2019;Azaki & Cresswell, 2021). The fact that feeding crows delayed their escape once the predator has been detected (reflected through greater BD) is consistent with the optimal escape theory (Ydenberg & Dill, 1986).…”