Arnaud Da Silva

Light pollution alters the phenology of dawn and dusk singing in common European songbirds

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.

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

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.

Melanin-based colour polymorphism signals aggressive personality in nest and territory defence in the tawny owl (Strix aluco)

Nest and territory defence are risky and potentially dangerous behaviours. If the resolution of life history trade-offs differs between individuals, the level of defence may also vary among individuals. Because melanin-based colour traits can be associated with life history strategies, differently coloured individuals may display different nest and territory defence strategies. We investigated this issue in the colour polymorphic tawny owl (Strix aluco) for which plumage varies from dark to light reddish melanic. Accordingly, we found that (1) our presence induced a greater response (flying around) from dark-coloured than light-coloured females and (2) dark reddish males suffered lower nest predation rates than light-coloured males. In experimentally enlarged broods, the probability that females reacted after we played back the hoot calls of a stranger male was higher if these females were lighter reddish; the opposite pattern was found in experimentally reduced broods with dark parents being more reactive than light parents. Finally, darker females alarmed more frequently when paired with a light than with a dark male, suggesting that partners adjust their behaviour to each other. We also tested whether colouration is used as a signal by conspecifics to adjust the level of their defensive behaviour. Accordingly, breeding females responded more vigorously to a dark than a light reddish stuffed tawny owl placed beside their nest. We conclude that melanin-based colouration is a signal of alternative nest and territory defence behaviour that depends on ecological factors.

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

The disruption of daily rhythms is one of the most studied ecological consequences of light pollution. Previous work showed that several songbird species initiated dawn song earlier in areas with light pollution. However, the mechanisms underlying this shift are still unknown. Individuals may immediately adjust their timing of singing to the presence of artificial light (behavioural plasticity), but the observed effect may also be due to phenotype-dependent habitat choice, effects of conditions during early life or micro-evolution. The main aim of this study was to experimentally investigate how males of four common passerine species respond to day-to-day variation in the presence of artificial night lighting in terms of the timing of singing. During two consecutive breeding seasons, we manipulated the presence of light throughout the night in a cyclic fashion in several naturally undisturbed forest patches. We show that individuals of all four species immediately and reversibly adjusted their onset of dawn singing in response to artificial light. The effect was strongest in the European robin, but relatively small in the blue tit, the great tit and the blackbird. The effect in the latter two species was smaller than expected from the correlational studies. This may be coincidence (small sample size of this study), but it could also indicate that there are longer-term effects of living in light-polluted urban areas on timing of dawn singing, or that birds use compensatory behaviours such as light avoidance. We found no evidence that our light treatment had carryover effects into the subsequent dark period, but robins progressively advanced their dawn singing during the light treatment.

Experimental illumination of a forest: no effects of lights of different colours on the onset of the dawn chorus in songbirds

Light pollution is increasing exponentially, but its impact on animal behaviour is still poorly understood. For songbirds, the most repeatable finding is that artificial night lighting leads to an earlier daily onset of dawn singing. Most of these studies are, however, correlational and cannot entirely dissociate effects of light pollution from other effects of urbanization. In addition, there are no studies in which the effects of different light colours on singing have been tested. Here, we investigated whether the timing of dawn singing in wild songbirds is influenced by artificial light using an experimental set-up with conventional street lights. We illuminated eight previously dark forest edges with white, green, red or no light, and recorded daily onset of dawn singing during the breeding season. Based on earlier work, we predicted that onset of singing would be earlier in the lighted treatments, with the strongest effects in the early-singing species. However, we found no significant effect of the experimental night lighting (of any colour) in the 14 species for which we obtained sufficient data. Confounding effects of urbanization in previous studies may explain these results, but we also suggest that the experimental night lighting may not have been strong enough to have an effect on singing.

Reciprocal preening and food sharing in colour-polymorphic nestling barn owls

Barn owl (Tyto alba) siblings preen and offer food items to one another, behaviours that can be considered prosocial because they benefit a conspecific by relieving distress or need. In experimental broods, we analysed whether such behaviours were reciprocated, preferentially exchanged between specific phenotypes, performed to avoid harassment and food theft or signals of hierarchy status. Three of the results are consistent with the hypothesis of direct reciprocity. First, food sharing was reciprocated in three‐chick broods but not in pairs of siblings, that is when nestlings could choose a partner with whom to develop a reciprocating interaction. Second, a nestling was more likely to give a prey item to its sibling if the latter individual had preened the former. Third, siblings matched their investment in preening each other. Manipulation of age hierarchy showed that food stealing was directed towards older siblings but was not performed to compensate for a low level of cooperation received. Social behaviours were related to melanin‐based coloration, suggesting that animals may signal their propensity to interact socially. The most prosocial phenotype (darker reddish) was also the phenotype that stole more food, and the effect of coloration on prosocial behaviour depended upon rank and sex, suggesting that colour‐related prosociality is state dependent.

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

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.

Nocturnal, diurnal and bimodal patterns of locomotion, sibling interactions and sleep in nestling Barn Owls

AbstractTemporal variation in physical activity is mainly determined by the day–night cycle. While this may be true for diurnal species whose vision at night is often poor, the situation might be more complex in nocturnal animals as many such species can see both in the dark and in the daylight. We examined in Barn Owl (Tyto alba) nestlings whether temporal variation of behavioural activities and sleep is shaped by parental feeding visits occurring during the first part of the night and the extent to which they also occur during daylight hours. We measured several behaviours in 280 individuals from 90 broods recorded in 4 years. Parental feeding visits progressively declined in frequency from the beginning to the end of the night, and a number of offspring behaviours followed the same pattern of activity (feeding, vocalization and self-preening). Surprisingly, nestlings were awake not only at sunset, but also at sunrise. Several behaviours (locomotion, wing flapping and sibling interactions, such as pecking and allopreening among nestlings) showed peaks of activity at sunset and sunrise, suggesting that they were performed for other reasons than to interact with parents. Allopreening was performed more often during the day than at night. We conclude that although adult Barn Owls are nocturnal, nestlings display a complex temporal pattern of activity that is governed not only by feeding but also by other unknown factors.ZusammenfassungNächtliche, tägliche und bimodale Muster der Lokomotion, der Interaktionen mit Geschwistern und des Schlafs bei Schleiereulennestlingen Der zeitliche Verlauf der körperlichen Aktivität wird hauptsächlich vom Tag-Nacht-Rhythmus bestimmt. Besonders tagaktive Arten sind oft nicht in der Lage nachts zu sehen, während nachtaktive Arten sowohl am Tag als auch nachts sehen können. Wir untersuchten an Schleiereulennestlingen (Tyto alba), ob zeitliche Variation von Verhalten und Gehirnaktivität von den elterlichen Besuchen in der ersten Hälfte der Nacht abhängen und ob Aktivitäten während des Tages ausgeführt werden. Wir bestimmten Verhaltensweisen von 280 Individuen aus 90 Bruten über vier Jahre. Elterliche Fütterungsbesuche nahmen über die Nacht stetig in der Frequenz ab, und einige der Verhaltensweisen der Nestlinge folgten diesem Muster (Fressen, Rufen und Putzen). Erstaunlicherweise waren Nestlinge nicht nur bei Sonnenuntergang wach, sondern auch bei Sonnenaufgang. Einige Verhaltensweisen (Lokomotion, Flügel schlagen und Interaktionen mit Geschwistern wie Picken und gegenseitiges Putzen) zeigten hohe Aktivität bei Sonnenuntergang und –aufgang, was darauf hindeutet, dass sie aus anderen Gründen ausgeführt wurden als mit den Eltern zu interagieren. Gegenseitiges Putzen wurde tagsüber öfter durchgeführt als nachts. Zusammenfassend ist zu sagen, dass Schleiereulen zwar nachtaktiv sind, Nestlinge aber ein komplexes Aktivitätsmuster zeigen, das durch die elterliche Fütterung vorgegeben ist, aber auch durch weitere, noch unbekannte Faktoren bestimmt ist.