It was found in English and Scottish tawny owls that the weight down to which males and females could survive starvation could go as low as in males and in females. In Spain, the average weight of 16 males was and for 19 females was . In total, weight can vary from in full grown tawny owls. Hearing is important for a nocturnal bird of prey, and as with other owls, the tawny owl's two ear openings differ in structure and are asymmetrically placed to improve directional hearing. A passage through the skull links the eardrums, and small differences in the time of arrival of a sound at each ear enables its source to be pinpointed. The left ear opening is higher on the head than the larger right ear and tilts downward, improving sensitivity to sounds from below. While the species does show the typical ear asymmetry of an owl and the right ear is consistently larger, the average differences of 7-13% are relatively modest for an owl. Both ear openings are hidden under the facial disk feathers, which are structurally specialized to be transparent to sound, and are supported by a movable fold of skin (the pre-aural flap). The ear slits average reportedly on the left and on the right. The movable pre-aural skin flap on tawny owl averages on the left and on the right. The tawny owls has a comparable ear morphology to the Ural owl ("Strix uralensis"). They tend to have a less complicated ear structure than those of "Asio" species but a more complicated, well-developed and relatively larger ear structure than those of other large generas of typical owl like the "Bubo" genus or "Otus" genus. The internal structure of the ear, which has large numbers of auditory neurons, gives an improved ability to detect low-frequency sounds at a distance, which could include rustling made by prey moving in vegetation. The tawny owl's hearing may be ten times better than a human's, and it can hunt using this sense alone in the dark of a woodland on an overcast night. However, the patter of raindrops can make it likely difficult for these owls to detect faint sounds, and prolonged wet weather, especially the crashing din of heavy rain, can lead to starvation if the owl cannot hunt effectively. The tawny's range is estimated to average 0.4-0.7 kHz with a maximum of around 3 kHz.