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

Abstract

The ecological impact of artificial light at night (ALAN) is an increasingly recognized process that accompanies expanding urbanization. Yet, we have limited knowledge on the impact of ALAN on wild species, and on the potential to mitigate any negative effects by using different light sources and colors. In birds, effects of ALAN on activity levels are reported for several species and, hence, their daily energy expenditure (DEE) may be affected. DEE is a potent mediator of life-history trade-offs and fitness and thus an important aspect to consider when examining the potential long-term ecological effects of ALAN. Previous work has suggested that birds exposed to ALAN show higher levels of provisioning and nocturnal activity, suggesting that white ALAN increases DEE. Other factors regulating DEE, such as provisioning behavior and food availability, might also respond to ALAN and thus indirectly affect DEE. We tested the hypothesis that ALAN increases DEE using an experimental setup where four previously unlit transects were illuminated with either white, green, or red LED light, or left dark as a control treatment. This setup was replicated in eight locations across the Netherlands. We measured DEE of our focal species, the great tit (Parus major), using a novel doubly labeled water technique that uses breath rather than blood samples. Contrary to our expectations, birds feeding their offspring under white and green ALAN showed lower DEE compared to birds in the control dark treatment. Differences in chick provisioning activity did not explain this result, as neither visit rates nor daily activity timing was affected by light treatment. However, food availability under white and green light was much higher compared to red light and the dark control. This difference strongly suggests that the lower DEE under white and green ALAN sites is a consequence of higher food availability in these treatments. This result shows that there can be positive, indirect effects of ALAN for breeding song birds which may balance against the negative direct effects shown in previous studies.

How to quantify animal activity from radio‐frequency identification (RFID) recordings

“…For example, applying a shorter than optimal cutoff rule would lead to an exponential increase of overrated visits, because individuals that stay longer at the nest than the used cutoff are counted twice (Lendvai et al, 2015). That happens in 90.0% of all visits when a cutoff of 6 s (blue tits; García-Navas et al, 2009) is applied to our video data, and 58.2% of all visits when a cutoff of 17 sec (great tits; Welbers et al, 2017) is used. These cited studies divided the processed registrations by two to calculate individual visit rates.…”

“…This arbitrary decision is based on the assumptions that the cutoff time is shorter than both the expected time spent outside (c.f., refractory period; Johnstone et al, 2014) and inside the nest and may have large implications for parameter accuracy (see Discussion). For example, earlier studies with passerine birds applied a cutoff of 6 s (blue tits: García-Navas, Ortego, & Sanz, 2009;Johnsen, Delhey, Schlicht, Peters, & Kempenaers, 2005) or 17 s (great tits, Parus major: Welbers et al, 2017). The remaining records were then divided by two to reach a visit rate for the given period.…”

Artificial light at night, in interaction with spring temperature, modulates timing of reproduction in a passerine bird

“…We have previously published caterpillar abundance and phenology data from our study sites (Welbers et al. ). While we have shown that green and white light strongly increased the availability of caterpillars, we have detected no effect of any light color on the timing of the spring caterpillar peak.…”

“…, Welbers et al. ). Similarly, annual changes in photoperiod modulate seasonal reproduction, molt, migration, immune function, and metabolic rate (Gwinner , Nelson and Demas , Bradshaw and Holzapfel , Hut , Helm et al.…”

“…An obvious reason why light pollution may alter several aspects of the behavior and ecology of wild species is the fact that organisms have evolved under predictable cycles of light and darkness dictated by the sun. Day length is indeed a key driver of daily rhythms of activity, sleep, body temperature, hormone secretion, and gene expression (Foster and Kreitzmann 2004, Roenneberg et al 2007, Wright et al 2013, Azzi et al 2014, Welbers et al 2017. Similarly, annual changes in photoperiod modulate seasonal reproduction, molt, migration, immune function, and metabolic rate (Gwinner 1987, Nelson and Demas 1997, Bradshaw and Holzapfel 2007, Hut 2011, Helm et al 2013.…”