The medium-sized Leisler's bat (Nyctalus leisleri) is similar in appearance to the noctule bat (Nyctalus noctula), but it is both darker and smaller. The fur is short, reddish-brown on the back and yellow-brown on the belly. Hairs on the back are dual coloured, being blackish-brown at the base, and reddish towards the tips. The wing membrane, face and ears are blackish-brown. Juveniles are darker in colour than adults.