Seasonal activity and behavioural responses to artificial light at night in migratory and non‐migratory sparrows

Urban and rural nocturnal environments are increasingly brighter due to artificial light at night (ALAN), causing wide‐ranging biological responses, from reproductive impairment to behavioural changes in diverse taxa. Songbirds may be particularly vulnerable, as their reproductive and migratory behaviours are under endogenous control and regulated by circannual and circadian clocks that are synchronized to daily light‐dark cycles. We hypothesized that increasing levels of ALAN will alter activity and behaviour in nocturnal migratory birds during migratory seasons more than non‐migrant species or during a stationary season, since migrants rely heavily on light cues to successfully complete migration. Here, we used captive experiments repeated across three seasons to compare the activity and behaviour of two nocturnal migrant sparrows, Gambel's white‐crowned Zonotrichia leucophrys gambelli and white‐throated sparrows Z. albicolis , and a non‐migrant house sparrow Passer domesticus . Birds were individually video recorded in captive indoor trials conducted in spring, summer, and autumn seasons, and tested under a range of ALAN intensities (0.15, 0.5, 1.5 and 10 lux) relative to a dark control (< 0.01 lux). We found that ALAN had little impact on P. domesticus total activity in any season and only subtly changed nocturnal behavioural patterns at the highest intensity. In Zonotrichia spp., both nocturnal activity and the expression of migratory restlessness (beak‐up and beak‐up‐flight) behaviours were altered by ALAN intensity across all seasons. Nocturnal restlessness followed a threshold response, being stimulated at low and moderate ALAN intensities, but diminished at 10 lux. Zonotrichia spp. also did not lower their diurnal activity to compensate for increased nocturnal activity, suggesting a possible energetic deficit. We speculate that changes to perceived photoperiod or nocturnal cues can interfere with the mechanisms that regulate activity and migratory behaviour, though further research is needed to determine if ALAN‐induced changes in activity have consequences for migration success, survival, and fitness in the wild.