Hibernation duration data
We compiled hibernation duration data from literature, publicly
available datasets, and our own field data. We also solicited data-based
estimates of hibernation duration from local bat researchers across
North America where few records were available from other sources (Table
S1, Figure S1). We restricted the study region for this analysis to
temperate North America (above the Tropic of Cancer and below the Arctic
Circle), although the published range of M. lucifugus extends
into the Arctic (Fenton and Barclay 1980). Spatially explicit records of
immergence and emergence collected from the literature generally
reported the average day of entrance or emergence, although some data
were presented only as the duration of hibernation. Where sex-specific
dates were given for a location, dates were averaged as insufficient
data existed to complete a sex-specific analysis.
Acoustic bat recorders (Songmeter SM2+BAT; Wildlife Acoustics, MA, USA)
were deployed by Wildlife Conservation Society Canada (WCS-C) to record
bat activity across western Canada between 2008 and 2016. Microphones
(either SMX-US or SMX-U1) were placed on 12-18-foot-tall telescoping
poles above likely hibernation or commuting areas (e.g. riverbanks,
cliff ridge tops) starting as early as mid-August. Acoustic activity was
typically recorded throughout the duration of the winter and data were
retrieved between mid-March and mid-May. Recordings were manually
analysed using AnalookW software (Titley Scientific, Inc.) and
customized noise-filters were used to pull files containing bat pulses.
The occurrence of at least 2 bat echolocation pulses in a file was
required to identify the recording as a ‘bat pass’, and the number of
passes were summed nightly. The start of the hibernation period was
defined by the last 3-night window between August 15 and December 31, in
which ≥10 passes were identified, while the end of the hibernation
period was defined by the first 3-night window between March 1 and May
15 in which ≥10 passes were recorded (Lausen and Barclay 2006). In
locations where bat activity was consistently low throughout the year
(spring and fall nightly activity often failing to exceed 10 passes),
hibernation start and end points were defined by date of the last and
first bat recordings, respectively. For sites with multiple years of
data, we took the mean immergence and emergence dates.