Characteristics of the nests, nestboxes, surrounding environment, laying females and their clutchesLEGEND - *Collected in the field. **Calculated electronically. ***Lamppost map created based on the Mapinfo data from the city of Montpellier (opendata.montpelliernumerique.fr/) with the Geographic Information System (QuantumGis 1.7.4), and then layered with the nestbox map to determine lamppost presence around nestboxes. ****Computed with Delta software providing maps and aerial pictures of the city of Montpellier. SITE AND NESTBOX CHARACTERISTICS – Site: five sites in Montpellier, France (1=Font Colombe, 2=Grammont, 3=Mas Nouguier, 4=Mosson, 5=Zoo du Lunaret). Boxidentity*: nestbox number giving their identity. BoxtypeClass and Boxtype*: 2=small wood-concrete Schwegler versus 3=medium larch-wood versus 4=large larch-wood nestboxes. Year: the 6 years of study (2011 to 2016). BIOLOGICAL MEASUREMENTS AT NEST – Nestheight*: vertical height of the external nest wall (to the nearest 0.25 cm). Nestvolume**: nest volume calculated in multiplying nest height by the internal surface of the bottom of the nest chamber (cm3). Firsteggdate*: laying date of the first egg in a clutch (Julian date from January 1). Clutchsize*: clutch size from the second half of March onwards till mid-July. Stage: reproductive stage (nest measured 1=during the week before egg-laying versus 2=during egg-laying versus 3=after incubation onset). Clutchtype*: clutch type (1=first versus 2=second breeding attempts). FemaleRing*: female ring number giving the identity of the female parent. FemaleAge*: female age (1=yearling versus 2=older). FemaleMass*: female body mass to the nearest 0.1 g. FemaleTarsus*: female tarsus length to the nearest 0.01 mm. ENVIRONMENTAL MEASUREMENTS AT NEST AND TERRITORY – LamppostPresence***: lamppost presence (1=at least one lamppost within a 100 m radius around each nestbox vs. 0=none). Distance*: distance (0-50 m) between the entrance hole of each nestbox and the closest lamppost bulb. VerticalAngle*: the vertical angle (-2-90°) between the entrance hole of each nestbox and the closest lamppost bulb. HorizontalAngle*: the horizontal angle (0-180°) between the entrance hole of each nestbox and the closest lamppost bulb. PermanentCover*: the light-blocking, permanent vegetation cover (in classes of 25% from 0 to 100%) between the entrance hole of each nestbox and the closest lamppost bulb. PC1LightAvailability**: night light availability at nest from the closest lamppost bulb as the first principal component PC1 (explaining 38.2% of the total variance, with distance to lamppost bulb=0.69, vertical angle=-0.58, horizontal angle= 0.59, light-blocking permanent vegetation cover=0.60) from the correlation matrix. Vegetation****: green spaces within a 50 m radius around each nestbox. Trees****: tree cover within a 50 m radius around each nestbox. Oak*: oak cover within a 50 m radius around each nestbox. PC1Cover**: vegetation cover as the first principal component PC1 (explaining 81.9% of the total variance, with green spaces =0.90, tree cover =0.96, oak cover = 0.86) from the correlation matrix.Holveck et al JAB data.txt

Both natural and artificial light have proximate influences on many aspects of avian biology, physiology and behaviour. To date artificial light at night is mostly considered as being a nuisance disrupting for instance sleep and reproduction of diurnal species. Here, we investigate if lamppost night lighting affects cavity-nesting bird species inside their breeding cavity. Nest height in secondary cavity-nesting species is the result of trade-offs between several selective forces. Predation is the prevailing force leading birds to build thin nests to increase the distance towards the entrance hole. A thin nest may also limit artificial light exposure at night. Yet, a minimum level of daylight inside nesting cavities is necessary for adequate visual communication and/or offspring development. Against this background, we hypothesised that avian nest-building behaviour varies in response to a change in night lighting. We monitored nest height of urban great tits (Parus major) during six years and found that it varied with artificial light proximity. The birds built thinner nests inside nestboxes of various sizes in response to increasing lamppost night light availability at the nest. In large nestboxes, the nests were also thinner when a lamppost was present in the territory. Whether this relationship between artificial night lighting and nest height reflects a positive or negative effect of urbanisation is discussed in the light of recent experimental studies conducted in rural populations by other research groups.