Seasonal and urban effects on the endocrinology of a wild passerine

Abstract

In order to maximize their fitness, organisms in seasonal environments rely on external cues to optimally time their life‐history stages. One of the most important zeitgeber to time reproduction is the photoperiod, but further environmental cues are assessed to fine‐tune reproduction due to year‐to‐year variation in environmental conditions. However, in urbanized environments, the pervasive artificial light at night has altered the natural signal of light and darkness. Accordingly, artificial light at night was repeatedly shown to affect avian reproductive physiology and to advance seasonal reproduction in birds. However, these experiments were mainly conducted in the absence of further environmental cues to facilitate the investigation of the mechanisms which are still poorly understood. Here, we investigate whether the endocrine system of free‐ranging European blackbirds (Turdus merula) correlates with the amount of artificial light at night along a rural to urban gradient while the birds still encounter complementary environmental cues including seasonal variation in day length and temperature. Testosterone and estrone were assessed as metabolites in fecal samples and corticosterone in blood from mist‐netted blackbirds. We demonstrate that seasonal fluctuations in abiotic factors, individual conditions, but also light at night affect the reproductive and stress physiology of wild European blackbirds. Elevated artificial night light intensities were significantly positively correlated with corticosterone and negatively with female estrone levels. No effects of artificial light were found for testosterone levels. Our results suggest that female blackbirds in particular perceive even low levels of artificial light at night as a weak but chronic stressor that interacts with the hypothalamic‐pituitary‐gonadal axis and leads to a reduced secretion of reproductive hormones. These findings point out that the impacts of light pollution are diverse and we only slowly disentangle its multiple effects on physiology, ecology, and biodiversity.

Behavioural plasticity in the onset of dawn song under intermittent experimental night lighting

“…Alternatively, birds may have roosted at the illuminated site, and may have been awake earlier due to the light, but may actively have chosen not to start singing. This choice may be conditional upon factors such as social stimulation (number of singing males; Foote, Fitzsimmons, Mennill, & Ratcliffe, 2011), body condition (Cuthill & Macdonald, 1990;Grava et al, 2009;Russ et al, 2015), personality (Naguib, van Rooij, Snijders, & van Oers, 2016), stress levels (Russ et al, 2015) or predation risk (Schmidt & Belinsky, 2013). The latter may play a role in our study, because night predators (owls) may be more numerous in forests than in cities (although evidence is equivocal, see Chamberlain et al, 2009), and are indeed common at the study site.…”

Artificial light at night alters behavior in laboratory and wild animals

“…The detection of the onset of day and night can therefore be altered (Dominoni & Partecke, ). Additionally, ALAN disrupts the daily corticosterone spike at the onset of activity, which alters waking cues (Russ et al., ) and disrupts the timing of morning arousal. Birds arise earlier with ALAN, and songbirds sing earlier in the morning, which can affect predator–prey interactions, as well as mating (Kempenaers, Borgström, Loës, Schlicht, & Valcu, ; Miller, ).…”

Nest height is affected by lamppost lighting proximity in addition to nestbox size in urban great tits

“…to improve sleep; Raap et al 2015Raap et al , 2016c. Artificial night lighting can be perceived as a chronic stressor (Russ et al 2015), well-known to modify bird stress physiology, depress their prolactin level, and, in turn, affect the current parental effort (Angelier and Chastel 2009). Yet, the avoidance of artificial light appears independent of female condition: in our study, higher-condition individuals do not seem to avoid artificial light at night more than individuals in lower condition do, and to force the later to occupy the nestboxes closest to lampposts.…”