DOI: 10.5061/dryad.8sf7m0czk
title: Breeding phenology and postnatal development data of northern bats (Eptesicus nilssonii)

description: Bats inhabiting northern latitudes are faced with short reproductive
 seasons during which they must produce and rear pups before fattening up
 in time to survive the winter hibernation. Therefore, the timing of
 parturition has considerable impacts on future fitness prospects for
 mother and pup. However, little is known about individual variation in
 breeding phenology and its consequences for postnatal development within
 bat populations. Here, we studied the phenology of breeding in Eptesicus
 nilssonii across seven years using data collected by day-to-day monitoring
 of a breeding colony in Norway (60.1°N) for which the identity and age of
 each mother (N = 8) and pup (N = 28) were known. Using mixed-effect
 models, we found that arrival at the colony was influenced by temperature
 conditions from mid-April to mid-May across all females, but that there
 were strong and consistent individual differences in arrival- and
 parturition time across years. Females generally arrived ~32.1 days before
 giving birth but the gestation duration was reduced if females arrived
 late, and prolonged if females left the colony when faced with cold
 weather conditions. Pups born later in the season were born smaller but
 had higher growth rates during the most rapid growth period (&lt;10
 days old). The within-individual effects suggest that the higher growth
 rates could be due to mothers compensating (e.g. through increased food
 intake) for late parturition rather than by improved food availability.
 Date of parturition did not influence adult body size in pups. Pups became
 volant at the earliest only 13.1 days after birth and approached adult
 flight patterns during their first flight week. Our results suggest that
 E. nilssonii is highly adapted to a short breeding season by producing
 large, fast developing and early volant pups, despite the environmental
 pressures bats face at northern latitudes.
description: # Breeding phenology and postnatal development data of northern bats
 (Eptesicus nilssonii)
 [https://doi.org/10.5061/dryad.8sf7m0czk](https://doi.org/10.5061/dryad.8sf7m0czk) ## Description of the data and file structure Data on breeding phenology and postnatal development in Eptesicuss nilssonii, collected in a small maternity colony in Nittedal (Norway) between 2017-2023. Missing values in the dataset are indicated with NA. The excel-file contains 8 spread-sheets, described in more detail below: **Spreadsheet Baby growth** A dataset which contains details on the development (forearm-length and body mass) of each pup born during the study period. The variables are the following: Year: the year the observation was made TimeDate: the date and time of the observation BabyBorn: the date the observed pup was born Baby: ID of the pup Sex: sex of the pup HoursOld: age of pup at observation, reported in hours (negative values indicate time before pup was born) DaysOld: age of pup at observation, reported in days (negative values indicate time before pup was born) Forearm: forearm length of pup, measured in mm Weight: body mass of pup, measured in grams Mother: ID of the mother MotherWeight: body mass of mother, measured in grams MotherFA: forearm length of mother, measured in mm MotherBorn: year of birth of the mother MotherAge: age of the mother **Spreadsheet Phenology** Data on phenology and yearly observations. The variables are the following: Year: the year the observation was made Spring_Onset: ordinal day of spring, calculated as the ordinal day where the 10-day smoothed daily temperature is above 0C for at least 10 days Mother: ID of the mother Mother age: Age of the mother Mother_arriving: Date the mother arrived in the bat box in spring Days from arrival to birth: Number of days from arriving in the box until giving birth Days missing early: Number of days mother is missing from the box in early pregnancy (less than 16 days after arriving in the box in spring) Days missing late: Number of days mother is missing from the box in late pregnancy (more than 15 days after arriving in the box in spring) Baby: ID of pup Sex: Sex of pup Born: Date and time pup was born BP lm growth: linear growth rate of forearm length of pup during the most rapid growth period (before 10.6 days old) Adultsize_FA: Largest recorded forearm length in pup Mom_FA: Forearm length of mother BP BM lm growth: linear growth rate of body mass of pup during the most rapid growth period (before 9.6 days old) Max BM 20days: Highest recorded body mass of pup before it was 20 days old Umb cord last obs: Time of last observation of umbilical cord being attached Umb cord age: Age of pup when umbilical cord was last observed being attached OpenEyes: Time of eyes being open for the first time Age_OpenEyes: Age of pup when opening eyes First_flight: Time for pup's first flight  Age first flight: Age of pup at first flight Mother leaving first time: Date of mother leaving the colony for the first time in the late summer Baby leaving: Date of pup leaving the colony for the first time in the late summer  Age leaving: Age of pup when leaving the colony for the first time **Spreadsheet GLM data arrival** Data for binomial model to predict probabilities of mother leaving the bat box during the gestation period.  The variables are the following: Year: the year the observation was made Mother: ID of the mother StartDate: Date of observation Present: Value indicating if mother is present (1) or not present (0) in the box Birth: Date and time for the birth of the pup Time_left: Days left until birth Days after arrival: Number of days since mother arrived in the box in spring Spreadsheet Weather three weeks to birth Meteorological data during the three weeks before a pup was born. The variables are the following: Baby: ID of pup Born: Birth date and time of pup DateTime: Date and time for meteorological observation Year: Year of observation Min temp: Minimum temperature measured past hour Max temp: Maximum temperature measured past hour Measured temp: Temperature measured Rain mm: Total rainfall (in mm) the past hour Wind ms: Mean wind speed (ms) the past hour MaxWind ms: Max wind speed (ms) the past hour Station ID: ID of meteorological station StationName: Name of meteorological station Sunrise next day: Date and time of the following sunrise Sunset: Date and time of the sunset Day night: Whether the observation was made during the day (before sunset) or during the night (after sunset) **Spreadsheet Environmental data (hourly)** Hourly meteorological data each summer of observing. The variables are the following: DateTime: Date and time for meteorological observation Year: Year of observation Min temp: Minimum temperature measured past hour Max temp: Maximum temperature measured past hour Measured temp: Temperature measured Rain mm: Total rainfall (in mm) the past hour Wind ms: Mean wind speed (ms) the past hour MaxWind ms: Max wind speed (ms) the past hour Station ID: ID of meteorological station StationName: Name of meteorological station Sunrise next day: Date and time of the following sunrise Sunset: Date and time of the sunset Month: Month the observation was made Day night: Whether the observation was made during the day (before sunset) or during the night (after sunset) **Spreadsheet Env data 3 weeks babygrowth** Meteorological data during the three weeks after a pup was born. The variables are the following: Baby: ID of pup Born: Birth date and time of pup DateTime: Date and time for meteorological observation Year: Year of observation Min temp: Minimum temperature measured past hour Max temp: Maximum temperature measured past hour Measured temp: Temperature measured Rain mm: Total rainfall (in mm) the past hour Wind ms: Mean wind speed (ms) the past hour MaxWind ms: Max wind speed (ms) the past hour Humidity: relative humidity in the air (%) Station ID: ID of meteorological station StationName: Name of meteorological station Sunrise next day: Date and time of the following sunrise Sunset: Date and time of the sunset Month: Month the observation was made Day night: Whether the observation was made during the day (before sunset) or during the night (after sunset) **Spreadsheet Emergence juveniles** Observations of emergence time of juveniles. The variables are the following: Year: Year of observation StartDate: Date (before midnight) of the observation DateTime leave: Date and time for emerging from the box at night  StartDate figure: Date (before midnight) of the observation, with the year changed to a common year for visualisation purposes DateTime figure: Date and time for emerging from the box at night, with the year changed to a common year for visualisation purposes Age: Whether observation is for a pup (juvenile) or mother (adult) FN_Karl: Flight night (1 is the first night pup flew out, 2 is the second, etc) of the pup with the ID Karl FN_PerOle: Flight night of the pup with the ID PerOle FN_MJ: Flight night of the pup with the ID Marie-Jo FN_Paul: Flight night of the pup with the ID Paul FN_Rune: Flight night of the pup with the ID Rune FN_Moritz: Flight night of the pup with the ID Moritz FN_Age: Flight night of the pup with the ID Age FN_Tony: Flight night of the pup with the ID Tony FN_PerInge: Flight night of the pup with the ID PerInge **Spreadsheet Trip duration juveniles** Observations of trip durations during foraging flights of juveniles. The variables are the following: Year: Year of observation StartDate: Date (before midnight) of the observation DateTime leave: Date and time for leaving the box at night  DateTime return: Date and time for returning after leaving flight duration min: Duration from leaving until returning (in minutes) pause time: time from returning until flying out again Number trips: number of trips registered for an individual Trip type: Type of trips, either "main" (first trip of the night) or "extra" (any trips made after the main trip) Age: Whether observation is for a pup (juvenile) or mother (adult) Flight night: Flight night of pup (1 is the first night pup flew out, 2 is the second, etc) ## Code/software Excel can be used to view the data file