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

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.