Gulls of a feather do not sleep whenever\u2014circadian rhythm of activity of black-headed gulls Chroicocephalus ridibundus during the incubation period

Piotr Indykiewicz,Julita Gerke,Dariusz Jakubas

doi:10.1007/s10336-021-01896-8

Abstract

Many vertebrates exhibit a diel activity, steered by light–dark cycle. However, some colonial waterbirds, in that several species of gulls, are active not only in day hours but also at night. In this study, we aimed to investigate 24 h cycle of black-headed gulls (BHG) Chroicocephalus ridibundus activity with focus on sleep behaviour. We expected that 24 h patterns of activity differ between colonies located in various habitats, and within a colony between nests located in the centre vs at the edge. We studied behaviour based on 9600 of 30 s videos from camera-traps taken in six colonies and data from 10 GPS-tracked individuals from one colony recorded during incubation. BHGs stayed active on average during 48.1% of a night, mainly spent on passive and active nest defence, and on nest maintenance. BHGs spent similar time on these activities in day hours. Individuals breeding in the colony centre slept at night longer than those at its edge. BHGs stayed active during on average 76.5% of daytime. In two urban colonies with the highest nest densities and highest level of light pollution birds slept less during the day than in other studied colonies (three rural and one urban) characterized by lower densities and light intensity after sunset near the colony. Knowledge of nocturnal behaviour is crucial to comprehend 24 h activity patterns of an organism, especially to understand flexibility of behaviour crucial for restoration, like sleep.

Highlights

Gulls, as many other groups of birds, are commonly considered active only during the day (Burger 1988; Yorio et al 2005; Hayes and Hayward 2020)
We found that blackheaded gulls (BHG) were active at day, and in late evening and at night
We found that BHG partners that remained in nests during incubation of eggs spent on sleep 48.1 ± 43.3% of 30 s nocturnal recordings, and 23.5 ± 35.3% of 30 s diurnal recordings in each colony

Summary

Introduction

As many other groups of birds, are commonly considered active only during the day (Burger 1988; Yorio et al 2005; Hayes and Hayward 2020). Some colonial waterbirds including at least 20 species of gulls have been reported to be active at night (Burger and Staine 1993; McNeil et al 1992, 1993). Knowledge on nocturnal activity of gulls is poor and fragmentary, and considers mainly night foraging or feeding chicks, and copulations at night (e.g., Leck 1971; Underhill 1987; Tarburton 1991; Yorio et al 2005), but not the entire spectrum of their activities at night. Other gull species do it irregularly, and rather in favourable environmental conditions, as moonlight in cloudless nights or artificial light from trawlers, lighthouses and airports. Regular studies of other aspects of nocturnal activities in gulls, e.g. interactions with neighbours, synchronizing timing of sleep with activities of the closest neighbours in a colony (so-called collective waves of sleep—Beauchamp 2011; Evans et al 2018), or full time budget, are rare

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