Roosting behaviour and roost selection of female big brown bats (Eptesicus fuscus) roosting in rock crevices in southeastern Alberta

We studied big brown bats (Eptesicus fuscus) roosting in rock crevices along the South Saskatchewan River in southeastern Alberta. We documented roosting behaviour and roost selection. During pregnancy and lactation, individuals aggregated as several small groups or one large group (maternity colony). Postlactating females roosted alone more frequently. During postlactation, individuals periodically returned to roost with a group dominated by pups, between periods of roosting alone. We identified 72 roosts used by members of the colony. Adult females switched roosts frequently and few roosts (24%) were reused. During pregnancy and lactation, the colony roosted in a 1.25-km length of the river valley on the northwest side of the river. With the onset of postlactation, females began roosting on both sides of the river and within a longer section of the river valley, and roosts faced in a more southerly direction. Crevices selected as roosts were more vertical in orientation, were farther from level ground above, and had openings that were smaller than those randomly available. Roosts used during pregnancy, lactation, and postlactation differed in physical attributes; lactation roosts were deeper and had larger openings. Selection of crevices with particular attributes suggested that selection was based on microclimate and avoidance of predation.