Sleeping Eurasian oystercatchers adjust their vigilance in response to the behaviour of neighbours, human disturbance and environmental conditions

M Mcblain,K A Jones,G Shannon,Andrew Kitchener

doi:10.1111/jzo.12812

Abstract

AbstractVigilance is a costly behaviour but it enables animals to detect and avoid threats of predation and intraspecific competition. To compensate for the increased risk while sleeping, many bird species have evolved eye‐blinking strategies called peeking, which allows vigilance to persist in a sleep‐like state. However, the drivers of vigilance behaviour during sleep have rarely been explored. We investigated how social factors, anthropogenic disturbance and environmental conditions affected the sleep‐vigilance trade‐off in the Eurasian oystercatcher (Haematopus ostralegus). Data were collected on the frequency, total duration and average duration of peeking at two locations on the Menai Strait, North Wales. Our results reveal that exposure to anthropogenic disturbance, particularly the presence of people exercising dogs, led to an increase in vigilance duration and reduced time sleeping, while increasing boat traffic resulted in elevated levels of peek frequency, but the overall duration of vigilance was in fact reduced. Furthermore, oystercatchers adjust their vigilance behaviour according to social context, with reduced levels of individual vigilance when a greater number of animals were present. However, if surrounding neighbours were awake – then the observed animal was more likely to be alert, demonstrating the importance of monitoring the behaviour of conspecifics. Likewise, the temperature and wind speed influenced vigilance with elevated levels of peek frequency observed in warmer and windier conditions. Oystercatchers are able to make fine‐scale adjustments to their vigilance behaviour while asleep, which reduces the risk of external threats such as predators. Nevertheless, they are making these decisions against the backdrop of a finely balanced energy budget, particularly during the winter months. Increased levels of human activity and disturbance may elevate the costs of vigilance and ultimately have fitness implications for this species.

Highlights

Vigilance enables animals to mediate risk by actively monitoring their surroundings and detecting an approaching threat (Beauchamp, 2015)
Our results reveal that exposure to anthropogenic disturbance, the presence of people exercising dogs, led to an increase in vigilance duration and reduced time sleeping, while increasing boat traffic resulted in elevated levels of peek frequency, but the overall duration of vigilance was reduced
Our study has highlighted that sleeping oystercatchers adjust their vigilance behaviour as a function of anthropogenic disturbance, but the specific approach is dependent upon the source of disturbance

Summary

Introduction

Vigilance enables animals to mediate risk by actively monitoring their surroundings and detecting an approaching threat (Beauchamp, 2015). Group size has been shown to have an important influence on vigilance behaviour, whereby increasing numbers of animals within a group results in the reduction of an individual’s investment in vigilance (Beauchamp, 2008) This is due to a greater level of collective threat detection (many eyes hypothesis: Pulliam, 1973; Lima, 1995), a reduced probability that a single animal will be targeted (dilution effect: Dehn, 1990) and the greater challenge of a predator singling out a specific individual in a rapidly moving group (confusion effect: Landeau & Terborgh, 1986; Olson et al, 2013). There is considerable variability in predation risk experienced by animals within the same group (Eshel, Sansone & Shaked, 2011), which is a function of location (i.e. greater risk at the edge of the group: Rattenborg et al, 1999a; Hirsch & Morrell, 2011), age, body size and dominance (Pravosudov & Grubb, 1998; Pravosudov & Grubb, 1999)

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