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

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.

Colony‐nesting gulls restrict activity levels of a native top carnivore during the breeding season

“…Specifically, we theorized that otter activity would be lowest towards the end of the chick‐rearing period, when gulls had invested the maximum amount of total energy into raising the chicks and would therefore respond strongest to otter activity within this timeframe. Given that most gull species are diurnal and have a reduced ability to see at night (Burger, 1988; Hayes & Hayward, 2020; Indykiewicz et al., 2021; Yorio et al., 2005), we hypothesized that otters would be predominantly nocturnal during the breeding season to access colonies when gulls are most vulnerable. Lastly, we aimed to verify if distance to nearest nest had any effect on otter sightings on nearby cameras traps within and outside of the breeding season.…”

Helminths of the black-headed gull (Chroicocephalus ridibundus) from breeding colonies in north-central Poland

“…Parasitological examination was performed in 2017–2019 on 43 black-headed gulls found dead in breeding colonies situated in north-central Poland, in the Kuyavian–Pomeranian Voivodeship, on small islands in lakes Kusowskie, Koronowskie, and Pakoskie, as well as on the River Brda flowing through Bydgoszcz and on an island in the active gravel pit Skoki Duże, a Natura 2000 protected area for birds. A detailed description of the islands and the size of the colonies are presented in works by Kitowski et al 18 , Jakubas et al 19 and Indykiewicz et al 20 . Parasites were identified using standard methods, including fixation, staining, and preparation of microscope slides.…”