DOI: 10.5061/dryad.sn02v6x7r
title: The risk faced by the early bat: individual plasticity and mortality costs of the timing of spring departure after hibernation

description: Hibernation is a widespread adaptation in animals to seasonally changing
 environmental conditions. In the face of global anthropogenic change,
 information about plastic adjustments to environmental conditions and
 associated mortality costs are urgently needed to assess population
 persistence of hibernating species. Here, we used a five-year data set of
 1,047 RFID-tagged individuals from two bat species, Myotis nattereri and
 Myotis daubentonii that were automatically recorded each time they entered
 or left a hibernaculum. Because the two species differ in foraging
 strategy and activity pattern during winter, we expected species–specific
 responses in the timing of hibernation relative to environmental
 conditions, as well as different mortality costs of early departure from
 the hibernaculum in spring. Applying mixed-effects modelling, we were able
 to disentangle population-level and individual-level plasticity in the
 timing of departure. To estimate mortality costs of early departure, we
 used both a capture mark recapture analysis and a novel approach that
 takes into account individual exposure times to mortality outside the
 hibernaculum. We found that the timing of departure varied between species
 as well as among and within individuals, and was plastically adjusted to
 large-scale weather conditions as measured by the NAO (North Atlantic
 Oscillation) index. Individuals of M. nattereri, which can exploit milder
 temperatures for foraging during winter, tuned departure more closely to
 the NAO index than individuals of M. daubentoniid which do not hunt during
 winter. Both analytical approaches used to estimate mortality costs showed
 that early departing individuals were less likely to survive until the
 subsequent hibernation period than individuals that departed later.
 Overall, our study demonstrates that individuals of long-lived hibernating
 bat species have the potential to plastically adjust to changing climatic
 conditions, although the potential for adjustment differs between species.
description: Bat capture and data
 logging We studied arrival (first recorded activity per
 hibernation period) and timing of departure from the hibernaculum (last
 recorded activity per hibernation period) of individually marked
 Natterer’s bats (M. nattereri n = 540) and Daubenton’s bats (M.
 daubentonii: n = 507) at a hibernaculum in North-Rhine Westphalia (Figure
 S1) (Stumpf et al. 2017,
 Meier et al. 2022). We
 caught bats using harp traps at the entrance of the hibernaculum, sexed
 them and distinguished two age classes, young of the year (1st
 hibernation) and adults (&gt;1 hibernation; for details
 see Reusch et al.
 2019). At this site,
 bats have been marked with
 individual RFID-tags (ID 100, Trovan) since 2002 for Natterer’s bats and
 since 2008 for Daubenton’s bats. Here, we focused on the years 2011 to 2015, for which
 we had continuous monitoring of bats entering and exiting the
 hibernaculum. All capture
 and marking were conducted
 under the permits (50.0835.2.1, 84-02.04.2015.A508, 70.2-2012/0254,
 70.2-0228/10, 70.2-0197/08 and 70.2.2.27), issued by
 the relevant
 authorities. The studied hibernaculum has two small entrances
 (8 cm x 5 cm), which were monitored by RFID-logger-antenna systems
 (LID-650, EURO I.D.). These systems continuously recorded the ID and a
 timestamp for all tagged individuals without interfering with the bats’
 behaviour (Reusch et al.
 2019, Meier et al. 2022).
 As only one antenna was employed per entrance, we could not directly
 assess whether a tagged bat entered or left the hibernaculum when detected
 by the RFID-logger. Therefore, we defined an arrival period (Aug 1st - Dec
 31st) and a departure period (Jan 1st - Apr 30th) for each hibernation
 (Ht) based on activity patterns known from direct observations in the
 field, light barrier recordings (that count the number of bats entering
 and emerging) and RFID recordings (as in Meier et al. 2022). For each individual and year, we determined the
 date of the last recording during the departure period (departure date of
 Ht) and the date of the first recording during the subsequent arrival
 period (arrival date of Ht+1). An individual was considered dead if it was
 not recorded in the subsequent hibernation period (Ht+1, Aug-Apr). We
 confirmed this assumption based on the available data: In our 5-year study
 period of continuous monitoring at the hibernaculum only one out of 1,047
 tagged individuals re-occurred after not being recorded during a complete
 hibernation period. Moreover, in 13 years of bat surveillance only 24 out
 of 1,111 bats (2.2 %) assigned dead according to the abovementioned
 criteria re-appeared at another RFID-monitored hibernaculum in close
 proximity to the study site (&lt; 500 m distance) for at least one
 more year [Grosche and Meier, unpublished data].
 To make sure that recorded
 individuals have indeed used the hibernaculum for hibernation, we excluded
 those individuals that had not been recorded during both, the arrival and
 the following departure period of a given hibernation period (Aug-Apr.; M.
 nattereri: 18 out of 540 individuals (3.3 %); M. daubentonii: 32 out of
 507 individuals (6.3).
description: Data file may be opened with excel, any text editor, and R. All
 Analyses were performed with R.