DOI: 10.5061/dryad.73n5tb2xq
title: Color of artificial light at night affects incubation behavior in the great tit, Parus major

description: Artificial light at night (ALAN) has been recognized as a biodiversity
 threat due to the drastic effects it can have on many organisms. In wild
 birds, artificial illumination alters many natural behaviors that are
 important for fitness, including chick provisioning. Although incubation
 is a key determinant of the early developmental environment, studies into
 the effects of ALAN on bird incubation behavior are lacking. We measured
 nest temperature in nest boxes of great tits during the incubation period
 in two consecutive years. Nest boxes were located in eight previously dark
 field sites that have been experimentally illuminated since 2012 with
 white, green, or red light, or were left dark. We tested if light
 treatment affected mean nest temperature, number of times birds leave the
 nest (off-bout frequency), and off-bout duration during the incubation
 period. Subsequently, we investigated if incubation behavior is related to
 fitness. We found that birds incubating in the white light during a cold,
 early spring had lower mean nest temperatures at the end of incubation,
 both during the day and during the night, compared to birds in the green
 light. Moreover, birds incubating in white light took fewer off-bouts, but
 off-bouts were on average longer. The opposite was true for birds breeding
 in the green light. Low incubation temperatures and few but long off-bouts
 can have severe consequences for developing embryos. In our study, eggs
 from birds that took on average few off-bouts needed more incubation days
 to hatch compared to eggs from birds that took many off-bouts.
 Nevertheless, we found no clear fitness effects of light treatment or
 incubation behavior on the number of hatchlings or hatchling weight. Our
 results add to the growing body of literature that shows that effects of
 ALAN can be subtle, can differ due to the spectral composition of light,
 and can be year-dependent. These subtle alterations of natural behaviors
 might not have severe fitness consequences in the short-term. However, in
 the long term they could add up, negatively affecting parent condition and
 survival as well as offspring recruitment, especially in urban
 environments where more environmental pollutants are present.
description: The data includes raw data, processed data, and R analysis
 scripts (original analysis in R version 4.02). Data consist of life
 history data and incubation behavior data from 103 great tit nests at 8
 experimental field sites in the Netherlands collected in the breeding
 seasons of 2016 and 2017. Nests were located around lamp posts that emit
 green, red, or white light at night, or no light. Measured incubation
 temperatures were summarized into five incubation behavior parameters per
 incubation day measured (raw temperature data and summarizing script not
 included here): mean day and night nest temperature; mean variation in
 night nest temperature; mean off-bout frequency; and mean off-bout
 duration. The latter two measures were inferred from the data by fitting a
 running mean (RM) with a time-window of 2h through the nest temperature
 data with any drops below RM denoting an off-bout. Days with gaps larger
 than 1h due to temperature logger malfunctioning were excluded, leaving
 1032 incubation days for 103 boxes. Additional model output tables and
 figures have also been included, which can be partly reproduced with the
 scripts.
description: All code needed to rerun the analyses can be found in the
 included R scripts, which also include descriptions of the data
 sets. This deposition includes two datasets
 (incubation-behaviour.RData and incubation-and-fitness.RData), three
 analysis scripts (script_analysis-nest-temp.R, script_analysis-offbouts.R,
 and script_analysis-fitness.R), and two word files with accompanying
 figures and tables respectively.