Short‐time exposure to light at night affects incubation patterns and correlates with subsequent body weight in great tits (Parus major)

Feb 8, 2024Journal of experimental zoology. Part A, Ecological and integrative physiology

Brief night-time light exposure changes nesting behavior and links to later body weight in great tits

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Abstract

Exposure to 4 hours of dim light resulted in a small advancing effect on activity onset in great tits.

Morning light exposure advanced activity onset in incubating great tits compared to dark controls.
Evening light exposure delayed activity offset compared to dark controls, but morning light did not have a similar effect.
Breeding success and chick condition remained unaffected by the light treatments.
Females exposed to artificial light at night had lower weights 9-18 days post-treatment, regardless of exposure timing.
These findings suggest potential physiological costs associated with artificial light exposure, despite a weak behavioral response.

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Artificial light at night (ALAN) widely affects wildlife by blurring light-dark differences, including transitions such as sunrise and sunset, thereby affecting regulation of diel rhythms. As a result, activity onsets in many wild diurnal songbirds advance under ALAN. From chronobiological studies, it is known that the direction and strength of the response to light depends on when during the night exposure takes place. However, these experiments are mostly done under continuous light conditions, when animals have free-running rhythms. It remains unclear whether phase-dependence also holds in entrained, wild songbirds; i.e., does the effect of ALAN on activity patterns differ between exposure in the morning compared to the evening? This information is essential to assess the effects of mitigation measures by limiting ALAN to selected times of the night. We exposed incubating great tits (Parus major) inside the nest-box to 4 h of dim light, of which 1 h overlapped with dawn before sunrise or dusk after sunset. We found a small advancing effect of morning-light on activity onset and of evening-light on offset compared to dark controls but not vice versa. Breeding success and chick condition were unaffected by the light treatments. However, light-treated females had lower weights 9-18 days after the end of the treatment compared to the controls, independent of whether ALAN occurred in the morning or the evening, indicating possible costs of ALAN. Despite the weak behavioral response, ALAN might have affected the females' circadian clock or physiology resulting in lower body condition.

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Short‐time exposure to light at night affects incubation patterns and correlates with subsequent body weight in great tits (Parus major)

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