Barn Owl
Have you ever wondered why owl faces are dish-like? Owls are highly reliant on their sense of hearing but birds don't have external ears like most mammals. I should add at this point that the "ears" on a Long-eared Owl are not real ears, but just decorative tufts of feathers: www.flickr.com/photos/timmelling/33818323195/in/photolist
The external part of the ear in mammals (called the pinna) helps gather sounds and if we cup our hands behind our ears it enhances our ability to detect sounds. An owl's dish-like face acts like a parabolic reflector, or maybe two giant pinnae on either side of the beak, gathering sounds and directing them to the ears, which are set asymmetrically on either side of the dish. The asymmetric setting of the ears apparently facilitates the pinpointing of rodent prey. Tim Birkhead's book "Bird Sense" mentions experiments done with a captive Barn Owl in total darkness where the owl could always capture a mouse on a floor covered with rustly leaves with pinpoint accuracy. But the owl would only do this if the light levels were reduced gradually and it was familiar with the surroundings. In an unfamiliar room in total darkness the owl would remain on its perch and would not attempt to catch a rustling mouse, presumably for fear of damaging its eyes on an unseen twig. When the owl did capture a mouse in total darkness it would always return instantly to its perch to avoid any unnecessary flying around where it could damage itself. The need for familiarity with the territory might explain why many nocturnal hunting owls don't move far. We know that birds can detect ultra violet light (invisible to us) but there was once a suggestion that owl's might perceive infra red light from the heat of the mouse. To test this the owl was placed in a room covered with foam rubber and a mouse was introduced with a rustly leaf tied to its tail. In total darkness the owl would always pounce on the leaf, not the mouse, showing that it was hearing (not infra red) that the owl relied on.
Barn Owl
Have you ever wondered why owl faces are dish-like? Owls are highly reliant on their sense of hearing but birds don't have external ears like most mammals. I should add at this point that the "ears" on a Long-eared Owl are not real ears, but just decorative tufts of feathers: www.flickr.com/photos/timmelling/33818323195/in/photolist
The external part of the ear in mammals (called the pinna) helps gather sounds and if we cup our hands behind our ears it enhances our ability to detect sounds. An owl's dish-like face acts like a parabolic reflector, or maybe two giant pinnae on either side of the beak, gathering sounds and directing them to the ears, which are set asymmetrically on either side of the dish. The asymmetric setting of the ears apparently facilitates the pinpointing of rodent prey. Tim Birkhead's book "Bird Sense" mentions experiments done with a captive Barn Owl in total darkness where the owl could always capture a mouse on a floor covered with rustly leaves with pinpoint accuracy. But the owl would only do this if the light levels were reduced gradually and it was familiar with the surroundings. In an unfamiliar room in total darkness the owl would remain on its perch and would not attempt to catch a rustling mouse, presumably for fear of damaging its eyes on an unseen twig. When the owl did capture a mouse in total darkness it would always return instantly to its perch to avoid any unnecessary flying around where it could damage itself. The need for familiarity with the territory might explain why many nocturnal hunting owls don't move far. We know that birds can detect ultra violet light (invisible to us) but there was once a suggestion that owl's might perceive infra red light from the heat of the mouse. To test this the owl was placed in a room covered with foam rubber and a mouse was introduced with a rustly leaf tied to its tail. In total darkness the owl would always pounce on the leaf, not the mouse, showing that it was hearing (not infra red) that the owl relied on.