Effects of nocturnal illumination on life-history decisions and fitness in two wild songbird species

Abstract

The effects of artificial night lighting on animal behaviour and fitness are largely unknown. Most studies report short-term consequences in locations that are also exposed to other anthropogenic disturbance. We know little about how the effects of nocturnal illumination vary with different light colour compositions. This is increasingly relevant as the use of LED lights becomes more common, and LED light colour composition can be easily adjusted. We experimentally illuminated previously dark natural habitat with white, green and red light, and measured the effects on life-history decisions and fitness in two free-living songbird species, the great tit ( Parus major ) and pied flycatcher ( Ficedula hypoleuca ) in two consecutive years. In 2013, but not in 2014, we found an effect of light treatment on lay date, and of the interaction of treatment and distance to the nearest lamp post on chick mass in great tits but not in pied flycatchers. We did not find an effect in either species of light treatment on breeding densities, clutch size, probability of brood failure, number of fledglings and adult survival. The finding that light colour may have differential effects opens up the possibility to mitigate negative ecological effects of nocturnal illumination by using different light spectra.

Artificial Light at Night Reduces Daily Energy Expenditure in Breeding Great Tits (Parus major)

“…Thus, our results might be a consequence of such non-random settlements rather than an effect of light on DEE, either direct or indirect. Although this explanation is unlikely (see additional discussion in de Jong et al, 2015), these results have important consequences for our understanding of the ecological impacts of ALAN. They suggest that when artificial illumination is localized in small rural and forest locations, its indirect effect of increased insect availability may offset the negative direct effects on stress and sleep disruption previously reported.…”

Stressful colours: corticosterone concentrations in a free-living songbird vary with the spectral composition of experimental illumination

“…As these spectra are eventually intended for civil use, light levels are normalized to lux at our experimental sites. Nine nest-boxes were placed in each transect ( [14]; 39% box occupancy). Adults were caught in the nest-box between 09.00 and 15.00 and between day 10 and 12 of chick rearing using a spring trap.…”

Experimental illumination of natural habitat—an experimental set-up to assess the direct and indirect ecological consequences of artificial light of different spectral composition

“…Changes in other types of daily behaviour may be more straightforward, such as a switch from daily to nocturnal foraging when light is present at night in feeding habitat [16,17]. Effects of artificial light on seasonal timing of birds have also been observed [18,19]. Changes in timing may be mediated by changes in hormone regulation [20], especially by melatonin [6,21].…”