Abstract
Artificial night lighting is expanding globally, but its ecological consequences remain little understood. Animals often use changes in day length as a cue to time seasonal behaviour. Artificial night lighting may influence the perception of day length, and may thus affect both circadian and circannual rhythms. Over a 3.5 month period, from winter to breeding, we recorded daily singing activity of six common songbird species in 12 woodland sites, half of which were affected by street lighting. We previously reported on analyses suggesting that artificial night lighting affects the daily timing of singing in five species. The main aim of this study was to investigate whether the presence of artificial night lighting is also associated with the seasonal occurrence of dawn and dusk singing. We found that in four species dawn and dusk singing developed earlier in the year at sites exposed to light pollution. We also examined the effects of weather conditions and found that rain and low temperatures negatively affected the occurrence of dawn and dusk singing. Our results support the hypothesis that artificial night lighting alters natural seasonal rhythms, independently of other effects of urbanization. The fitness consequences of the observed changes in seasonal timing of behaviour remain unknown.
Highlights
Urbanization proliferates worldwide at an unprecedented pace [1]
Similar to the dawn chorus, robins, blackbirds, great tits and blue tits were more likely to produce a dusk chorus earlier in the season in the lighted sites compared with the dark sites
Our results show that artificial night lighting is associated with the phenology of singing in all the songbird species in this study, except the chaffinch
Summary
Urbanization proliferates worldwide at an unprecedented pace [1]. Human activities related to urbanization lead to severe environmental changes, including habitat destruction, increasing local temperatures (‘heat-islands’ [2]) and chemical, noise and light pollution [3]. In blue tits, Cyanistes caeruleus, females exposed to street lighting started egg-laying on average 1.5 days earlier in the season than females breeding in dark territories in the same forest [14] Such effects of light pollution on seasonal timing are expected, at least in temperate regions, because individuals use photoperiod as a proximate cue to determine the time of breeding [21,22]. The primary aim of this study was to identify whether the occurrence of artificial night lighting is associated with changes in the phenology of the production of dawn and dusk singing in six common songbird species. We compare the strength of this seasonal effect in six songbird species for which we previously assessed the effect on the daily timing of singing [14,17] To this end, we recorded dawn and dusk song in 12 sites that varied in the presence of light (and noise) pollution. The secondary aim of our study was to examine the effects of weather conditions (i.e. rain and relative temperature) on the occurrence of dawn and dusk singing throughout the season
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