Singing from North to South: Latitudinal variation in timing of dawn singing under natural and artificial light conditions

Abstract

Animals breeding at northern latitudes experience drastic changes in daily light conditions during the breeding season with decreasing periods of darkness, whereas those living at lower latitudes are exposed to naturally dark nights throughout the year. Nowadays, many animals are also exposed to artificial night lighting (often referred to as light pollution). Animals strongly rely on variation in light levels to time their daily and seasonal behaviour. Previous work on passerine birds showed that artificial night lighting leads to earlier onset of dawn song. However, these studies were carried out at intermediate latitudes with more limited seasonal changes in daylength, and we still lack an understanding of the impact of artificial night lighting in relation to variation in natural light conditions. We investigated the influence of natural and artificial light conditions on the timing of dawn singing in five common songbird species in each of three regions in Europe that differed in natural variation in daylength (northern Finland, 65°N; southern Germany, 48°N; southern Spain, 37°N). In each region, we selected five peri-urban forest sites with and five without street lighting, and we recorded dawn singing at the beginning of the local breeding season. Our results show that the earliest natural singers, that is, European robins (Erithacus rubecula) and common blackbirds (Turdus merula), started dawn singing earlier along with the natural increase in night brightness in Finland, with no additional effects of artificial night lighting. In contrast, the later singers, such as, great tits (Parus major), blue tits (Cyanistes caeruleus) and chaffinches (Fringilla coelebs), showed similar onsets of dawn song relative to sunrise across the season and similar effects of artificial night lighting at all latitudes. Artificial night lighting affected great tits, blue tits and chaffinches even in northern Finland where nights became very bright. Proximate factors such as differential light sensitivities may explain why early singers showed more plastic behavioural responses to naturally and artificially bright nights. The maintenance of rhythmicity in the late singers during bright northern nights and under artificial night lighting may also be an adaptive response to predation risk or costs of sleep loss.

Assessing the effects of artificial light at night on biodiversity across latitude – Current knowledge gaps

“…Under ALAN conditions, it was advanced for latitude-insensitive species only (Da Silva & Kempenaers, 2017).…”

Cavities shield birds from effects of artificial light at night on sleep

“…Although our study was done during winter when both male and female great tits roost inside cavities and nest boxes, during the breeding season mainly females sleep inside nest boxes (Hinde, ; Kluijver, ). Males are therefore possibly exposed to higher levels of light pollution, which could explain results observed on dawn song, a typical male behavior in great tits (Da Silva & Kempenaers, ; Da Silva et al., ; ; ). In our current experimental study performed during the winter period, we did not find any effects of our light treatment on sleep behavior of male and female great tits.…”

“…Light pollution or artificial light at night (ALAN) is an increasing worldwide environmental alteration (Falchi et al, 2016) and we are just beginning to explore the multitude of its effects. Light pollution disrupts natural light cycles and potentially poses an important threat for wildlife, biodiversity, and humans (Duffy, Bennie, Duran, & Gaston, 2015;Gaston, Bennie, Davies, & Hopkins, 2013;Hölker, Wolter, Perkin, & Tockner, 2010;Kyba & Hölker, 2013;Navara & Nelson, 2007;Rich & Longcore, 2005), since it results in a wide range of physiological and behavioral responses (see, e.g., Da Silva & Kempenaers, 2017;Dominoni, Quetting, & Partecke, 2013). For example, in two cavitynesting songbird species, blue tits (Cyanistes caeruleus) and great tits (Parus major), sleep behavior was disrupted by experimental light inside the nest box (Raap, Pinxten, & Eens, 2015, 2016cRaap, Sun, Pinxten, & Eens, 2017c;Sun, Raap, Pinxten, & Eens, 2017).…”

What type of rigorous experiments are needed to investigate the impact of artificial light at night on individuals and populations?

“…In addition, a wider breadth of taxonomic diversity in response to "realistic" ALAN in natural habitats is necessary. Lastly, studies exploring latitudinal and photoperiod variation, which both regulate physiology, are likewise rare and needed (Da Silva & Kempenaers, 2017). Lastly, studies exploring latitudinal and photoperiod variation, which both regulate physiology, are likewise rare and needed (Da Silva & Kempenaers, 2017).…”

“…Studies of amphibian and reptile physiological responses to ALAN are rare, even though photosensitivity and melatonin response of these taxonomic groups is notably different from other vertebrates (Underwood, 1986). Lastly, studies exploring latitudinal and photoperiod variation, which both regulate physiology, are likewise rare and needed (Da Silva & Kempenaers, 2017).…”