DOI: 10.5281/zenodo.14478195
title: Temporal changes to foraging patterns in reproductive northern bats (Eptesicus nilssonii)

description: Description

In this dataset we present data on body mass, number of foraging trips (mean number at the colony-level), foraging durations (of the first trip of the night), and timing of first emergences and last returns. The r-script attached include codes for the models presented in the published article, titled "Female northern bats (Eptesicus nilssonii) respond to energetic demands of lactation by shifting foraging patterns".

 

Files and variables

Excel-file: Lilley_et_al.xlsx

The excel-file contains five different datasets, added as separate sheets. Below are descriptions of each dataset.

 

Dataset 1: mother_BM_df

General description of dataset:

Body mass data on reproductive E. nilssonii females before and after parturition during the breeding seasons of 2017-2023. Each female could be identified for these measurements, and we also knew the exact date of parturition for each individual female, which allowed us to investigate body mass changes on a detailed temporal scale across the reproduction.

 

Description of variables:

Year: The year of the observation.

TimeDate: The date and time of the weight-measurement (format: year-month-day hour:minute)

BabyBorn: The date and time of the birth of the pup belonging to the female that was measured (format: day-month-year hour:minute).

Baby: Name/ID of the pup.

Sex: Sex of the pup.

DaysOld: Age of the pup, in days. Negative values indicate that measurements are taken during pregnancy and specify the number of days left until birth, while positive values indicate that measurements are taken after the pup is born and therefore correspond to the age of the pup.

Mother: Name of the mother.

MotherWeight: Weight-measurement in grams.

Mother2: More generic ID of the mother.

rep_period: Stage of reproduction, either “Gestation” for pregnant females, or “Lactation” for lactating females.

summer_Ta: Mean temperature (Celsius) from 15th May to 15th July that year (annual value).

total_rain: Total rainfall (mm) from 15th May to 15th July that year (annual value).

 

Dataset 2: foraging_trips_df

General description of dataset:

Data on the mean number of trips made by the females in the colony each night (total number of trips/number of bats) in relation to the median parturition date in the colony, for the breeding season of 2021-2023. Trips were recorded with direction-sensitive infrared sensors (ChiroTec Tricorder 9006) installed at the box-entrance that recorded the timing of each emergence and return at night.

 

Description of variables:

Year: The year of the observation.

StartDate: Date of the trip-number observation (date correspond to date before midnight).

trips_per_bat: Mean number of trips per bat that night.

median_birth: Date for the median birth in the colony (format: date/month/year hour:minute) that year.

time_to_birth: Number of days left to (negative values) or since (positive values) the median birth date.

rep_period: Stage of reproduction, either “Gestation” for pregnant females, or “Lactation” for lactating females.

night_Ta: Mean temperature conditions (Celsius) for that night, based on hourly measurements.

night_rain: Total rainfall (mm) for that night.

 night_wind: Mean hourly wind conditions (m/s) for that night, based on hourly measurements.

night_length: Length of the night in hours.

 

Dataset 3: foraging_durations_df

General description of dataset:

Data on the duration of the ‘main’ foraging trips (first trips per bat each night) each night, from the breeding season of 2021-2023.

 

Description of variables:

Year: The year of the observation.

StartDate: Date of the trip-number observation (date correspond to date before midnight).

DateTime_leave: Date and time for the emergence (format: date/month/year hour:minute).

DateTime_return: Date and time for the return (format: date/month/year hour:minute).

Individual: ID of bats when possible to ID them – mainly just one individual (“Nikki”) as she was the only ringed bat in the colony these years.

duration_min: Duration of foraging trip in minutes.

duration_h: Duration of foraging trip in hours.

median_birth: Median date for the births in the colony (format: date/month/year hour:minute) that year.

time_to_birth: Number of days left to (negative values) or since (positive values) the median birth date.

rep_period: Stage of reproduction based on the date in relation to the median parturition date (either “Gestation” or “Lactation”).

night_Ta: Mean temperature conditions (Celsius) for that night, based on hourly measurements.

night_rain: Total rainfall (mm) for that night.

night_wind: Mean hourly wind conditions (m/s) for that night, based on hourly measurements.

night_length: Length of the night in hours.

 

Dataset 4: activity_out_df

General description of dataset:

Data on the timing of first emergences per night, from the breeding season of 2020-2023.

 

Description of variables:

Year: The year of the observation.

StartDate: Date of the emergence-observation (date correspond to date before midnight).

DateTime: Date and time for the emergence (format: date/month/year hour:minute).

Individual: ID of bats when possible to ID them – mainly just one individual (“Nikki”) as she was the only ringed bat in the colony these years.

sunset: Time of the sunset that night (format: date/month/year hour:minute).

sunrise: Time of the sunrise that night (format: date/month/year hour:minute).

time_since_sunset: Emergence time in relation to sunset (number of minutes since sunset).

night_length: Length of the night in hours.

sunset_Ta: Temperature (Celsius) at sunset.

sunset_rain: Total rainfall (mm) the last hour before sunset.

sunset_wind: Wind conditions (m/s) at sunset.

median_birth: Median date for the births in the colony (format: date/month/year hour:minute) that year.

time_to_birth: Number of days left to (negative values) or since (positive values) the median birth date.

rep_period: Stage of reproduction based on the date in relation to the median parturition date (either “Gestation” or “Lactation”).

 

Dataset 5: activity_in_df

General description of dataset:

Data on the timing of last returns per night, from the breeding season of 2020-2023.

 

Description of variables:

Year: The year of the observation.

StartDate: Date of the return-observation (date correspond to date before midnight).

DateTime: Date and time for the return (format: date/month/year hour:minute).

Individual: ID of bats when possible to ID them – mainly just one individual (“Nikki”) as she was the only ringed bat in the colony these years.

sunset: Time of the sunset that night (format: date/month/year hour:minute).

sunrise: Time of the sunrise that night (format: date/month/year hour:minute).

time_until_sunrise: Return time in relation to sunrise (number of minutes until sunrise).

night_length: Length of the night in hours.

median_birth: Median date for the births in the colony (format: date/month/year hour:minute) that year.

time_to_birth: Number of days left to (negative values) or since (positive values) the median birth date.

rep_period: Stage of reproduction based on the date in relation to the median parturition date (either “Gestation” or “Lactation”).

night_Ta: Mean temperature conditions (Celsius) at night, based on hourly measurements.

night_rain: Total nightly rainfall (mm).

night_wind: Mean wind conditions (m/s) at night, based on hourly measurements.

 

Code/software

The data is saved in an excel-file. A Microsoft-subscription is needed to access the data.

The codes are saved as an r-script. The free software R is needed to access the codes.
description: Article abstract:

Unpredictable environmental conditions affecting prey availability and short summer nights reducing foraging time present nocturnal insectivorous mammals with an energetic dilemma at northerly latitudes during gestation and lactation. This is pronounced for aerial hawking bat species, for which prey activity is highly dependent on ambient temperature. Here, we describe changes in activity of female Eptesicus nilssonii, the northernmost breeding bat species, switching from gestation to lactation at a roost site in southern Norway (60.1°N). Roost exits and returns were recorded using an infrared barrier at the entrance, and parturition dates were registered via a camera set inside the roost. Our results indicate significant temporal changes in behaviour throughout the breeding season, with lactating bats both setting out to forage earlier than during gestation and returning later. This behaviour is dependent on ambient temperature, with bats refraining extending foraging time at elevated temperatures. We infer these behaviours to occur as a response to the increased energetic needs of lactation, and the effect of increased temperature to reflect increased food availability which allows females to avoid increased predation pressure as a consequence of advanced roost exit or delayed return. Our study reveals mechanisms in high latitude insectivorous bats to cope with a short season with fluctuating resources.

 
description: Study system:

A small maternity colony (total Nind = 8) of E. nilssonii  was roosting in a bat box hanging 1.5 m above ground on a garage-wall in Nittedal, Norway (60.11°N, 10.85°E), during the breeding seasons of 2017 to 2023. 

In this dataset we present data on body mass, number of foraging trips (mean number at the colony-level), foraging durations (of the first trip of the night), and timing of first emergences and last returns.

Data collection:

Biometric measures (weights to nearest 0.1 g using a digital mini-weight and forearm-length to nearest 0.1 mm using dial callipers) of reproductive females were generally taken in the morning throughout the breeding season (five to 15 times per individual per season). Because the parturition dates were known for each female, we calculated the time relative to parturition for each measurement. Body mass data were collected each year from 2017 to 2023.

Before the breeding season of 2019 we installed a camera (D-link DSC-2670L) in the bat box, which provided motion-triggered video-recordings in addition to real-time observations (software mydlink, version 2.11.0, D-Link Corporation). Before the breeding season of 2020 we installed direction-sensitive infrared sensors (ChiroTec Tricorder 9006) at the box-entrance to record the timing of each emergence and return at night. Each pass registered by infrared sensors were checked against the motion-triggered video recordings to remove any false passes (i.e. if bats went to the exit, but did not fly out), to include passes that had been missed by infrared sensors, and to determine whether the recorded activity belonged to reproductive females or volant pups. Volant pups were distinguishable from adults on camera based on size and fur characteristics throughout their first flight week, after which the separation of volant pups and adults became increasingly challenging. Data on activity patterns therefore also include data from volant pups after they became undistinguishable from adults. However, pups adopt adult foraging patterns a week after gaining volancy, and we therefore do not expect the inclusion of such individuals to cause large impacts in the data; nevertheless, this could be a source of variation to activity patterns observed towards the end of the breeding season.

The colony was monitored across the breeding period through daily box checks and video recordings to determine individual timing of arrival and parturition.