Mid-Atlantic Big Brown and Eastern Red Bats: Relationships between Acoustic Activity and Reproductive Phenology

Abstract

Acoustic data are often used to describe bat activity, including habitat use within the summer reproductive period. These data inform management activities that potentially impact bats, currently a taxa of high conservation concern. To understand the relationship between acoustic and reproductive timing, we sampled big brown bats (Eptesicus fuscus) and eastern red bats (Lasiurus borealis) on 482 mist-netting and 35,410 passive acoustic sampling nights within the District of Columbia, Maryland, Pennsylvania, Virginia, and West Virginia, 2015–2018. We documented the proportion of female, pregnant, lactating, and juvenile big brown and eastern red bats within each mist-net sampling event and calculated locally estimated non-parametric scatterplot smoothing (LOESS) lines for each reproductive and acoustic dataset. We compared the peak in acoustic activity with the peaks of each reproductive condition. We determined that the highest levels of acoustic activity within the maternity season were most associated with the period wherein we captured the highest proportions of lactating bats, not juvenile bats, as often assumed.

Factors influencing the detection and occupancy of little brown bats (Myotis lucifugus)

“…We suggest that there may need to be greater survey effort at sites further from water due to the decreasing detection rate as distance to water increases if to 15 August (USFWS, 2023), there may be benefits to increasing levels of survey effort early in the field season. Detection probability increasing later in the summer is likely due to the young of the year taking flight (Kaiser & O'Keefe, 2015;Pauli et al, 2017)., increasing abundance and likelihood of detection (Clement et al, 2014) or possibly changes in foraging patterns through maternal progress (Deeley et al, 2022).…”

“…Detection probability increasing later in the summer is likely due to the young of the year taking flight (Kaiser & O'Keefe, 2015; Pauli et al., 2017). , increasing abundance and likelihood of detection (Clement et al., 2014) or possibly changes in foraging patterns through maternal progress (Deeley et al., 2022).…”

“…With additional acoustic recorders in other types of land cover such as grassland, residential, and agricultural fields, to comprehensively survey the available landscape for occupancy analysis. We hypothesized that date would influence detection as maternal condition changes through the active season and young become volant (Deeley et al., 2022 ; Fenton & Barclay, 1980 ) increasing the number of individuals in the population for detection (MacKenzie et al., 2017 ). This was also a consideration for detection due to bats using waterways as flight corridors and foraging on aquatic insects (Hagen & Sabo, 2011 ).…”

Conservation Value to Bats: Assessing Multiple Functional Habitats in a Nature Preserve at the Urban-Agricultural Interface via Temporal Ecology

“…These efforts yield a total of 402 detector nights. For each recording night, we calculated its Julian date as a covariate [32,33]. We extracted nightly minimum temperatures from VisualCrossing (https://www.visualcrossing.com/ accessed on 31 January 2023) as a survey covariate as bat activity responds to temperature variations [27].…”

“…Another aspect of temporal ecology is examining bat activity patterns across nights, months, or even years. At these scales, variation in bat activity may indicate life history events, such as arousals from hibernation [31], the arrival of migrators [32], preparation for lactation [33], or fall swarming and overwintering [34], which correspond to different resources provided by different habitats. In terms of foraging, bats generate unique feeding buzzes that can be recorded and identified to quantify foraging activity patterns [35,36].…”