Although 5 species of bats have been documented in Southeast Alaska, information on species not of the genus Myotis is derived solely from 4 specimens of the Silver-haired Bat (Lasionycteris noctivagans). We acoustically monitored for bat species that produce low frequency echolocation calls (<30 kHz minimum frequency), specifically Hoary Bat (Lasiurus cinereus), Silver-haired Bat, and Big Brown Bat (Eptesicus fuscus) at 40 sites in 16 locations across Southeast Alaska from 2011 to 2013 using passive bat detectors. The Hoary Bat was not previously known from Alaska, but we recorded 25 call files of this species (of 26,151 low frequency bat files) at 5 sites in northern Southeast Alaska (4 mainland sites and 1 site on Chichagof Island); an additional 110 call files were classified as probable Hoary Bat, but were ambiguous. We recorded 3075 call files that contained echolocation calls diagnostic of Silver-haired Bats; no files had characteristics diagnostic of Big Brown Bats. The rest of the low frequency recordings were identified as probable Silver-haired Bat calls, although Big Brown Bats cannot be ruled out due to the extensive overlap of acoustic characteristics between these 2 species. We recorded Hoary Bats almost exclusively during the autumn migration period. By contrast, Silver-haired Bats were detected throughout the summer active season, indicating at least some individuals are resident in Southeast Alaska. Silver-haired Bat activity was greatest at sites on or near the mainland, with most sites showing peaks of activity in spring, suggesting bats from the interior may be overwintering in the region. Winter recordings suggest Silver-haired Bats (and Big Brown Bats if present) are active to some extent during winter in Southeast Alaska. Understanding the distribution and seasonality of Hoary and Silver-haired Bat activity in Southeast Alaska is a critical 1st step toward identifying their habitat requirements and conservation needs in this region.