was linked to broad shifts in bird physiology and behavior, with life-history traits largely unchanged.
Evidence
This meta-analysis pooled 675 effect sizes from 36 studies across 30 bird species and found reduced sleep, higher metabolic rate, earlier and longer activity, and more nocturnal foraging under ALAN.
Caveat
The evidence synthesis found no life-history effect and the fitness consequences remain unresolved, despite stronger effects in migratory species, adults, females, and brighter light conditions.
Simplified
(ALAN) is a major anthropogenic pressure across the tree of life. While ALAN drives population declines in insects and reptiles, birds defy simple patterns. Avian responses to ALAN vary in direction and magnitude, yet the fitness consequences of these responses remain unresolved. We conducted a meta-analysis to test whether ALAN alters avian physiology, behaviour and life-histories, analysing 675 effect sizes from 36 studies across 30 species. We found consistent physiological and behavioural shifts under ALAN, while life-history traits were unaffected. ALAN disrupted physiology through reduced sleep, higher metabolic rate and accelerated reproductive maturation. Behaviourally, daily activity was extended, with earlier onset, later offset, and increased nocturnal activity and foraging effort. Subset analyses revealed stronger ALAN effects in migratory species compared to residents and more pronounced in adults and females than in nestlings and males. Activity shifts, accelerated ageing and sleep disruption were amplified with brighter light. Birds appeared to buffer ALAN effects through physiological and behavioural adjustments, minimising impacts on life-histories, a paradox likely explained by phenotypic plasticity or evolutionary adaptation. We identified key ecological vulnerabilities, emphasising the need for targeted conservation strategies in our increasingly illuminated world.
Key numbers
−1.496
Increased daily activity onset
Mean estimate from meta-analysis indicating shift in timing.
0.474
Higher metabolic rate
Mean estimate indicating physiological response to .
0.649
Accelerated reproductive maturation
Mean estimate reflecting changes in reproductive timing.
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Circadian Biology