Awake and hungry: artificial light at night disrupts behaviour and reproductive ecology in a wild migratory bird

Mar 31, 2026Proceedings. Biological sciences

Artificial Light at Night Disturbs Behavior and Breeding in a Wild Migratory Bird

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Abstract

ALAN-exposed nestlings begged more frequently and for longer at night compared to dark controls.

Exposure to artificial light at night led to disrupted circadian activity in nestlings.
Both male and female parents adjusted their feeding schedules, starting earlier and finishing later.
Hourly feeding rates decreased for parents of ALAN-exposed nestlings compared to controls.
Nestlings exposed to ALAN fledged at older ages, indicating delayed development.
Reproductive success, measured as the number of fledged offspring, remained unaffected.

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Artificial light at night (ALAN) disrupts biological rhythms across taxa, yet behavioural mechanisms linking exposure to population consequences remain poorly understood. Long-distance migrants encounter ALAN across their annual cycle but remain understudied despite experiencing stronger performance impacts than sedentary species. We experimentally introduced ALAN into nest-boxes of a migratory passerine, the collared flycatcher (Ficedula albicollis), breeding in Gotland, Sweden. Nestlings were exposed to ALAN from 2 days post-hatching until fledging, and we video-recorded parental and nestling activity over 24 h on day 8 post-hatching. Across a high-resolution behavioural dataset (32 100 nestling and 3709 parental events), ALAN-exposed nestlings begged more frequently and for longer at night compared with dark controls, revealing disrupted circadian activity. These effects cascaded to parents: both females and males began feeding earlier and ceased later, while reducing hourly feeding rates relative to controls. Consequently, ALAN nestlings fledged at older ages, consistent with delayed development, though reproductive success (number of fledged offspring) was unaffected. Our study provides clear empirical support for socially mediated behavioural mechanisms whereby both parents respond to ALAN, disrupting family level coordination, developmental trajectories and parental investment. This temporal destabilization of social synchrony uncovers a novel ecological pathway through which anthropogenic light alters behavioural timekeeping and life-history trajectories in the wild.

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Awake and hungry: artificial light at night disrupts behaviour and reproductive ecology in a wild migratory bird

Abstract

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