Owls

The owls are the nocturnal version of diurnal raptors, with some similar physical and behavioural adaptations: They eat other animals, they use their feet to catch and kill prey and also to carry it to away.

All owls have large rounded forward facing eyes, similar to humans. Not all owl species only hunt at night- the majority hunt at dusk and dawn (known as crepuscular hunting) but some species prefer hunting during the daylight.

OWL FACTS

Owls use their very acute hearing to locate prey.
The Great Grey Owl is thought to be able to hear its prey (lemmings) upto 30cm (12inches) under the snow.
Most owls are cryptically coloured to prevent detection while roosting.
Owls with yellow coloured eyes (iris) are generally daytime hunters
Owls with orange coloured irises are generally crepuscular hunters (dusk and dawn)
Owls with dark coloured irises are usually nocturnal hunters
Smallest is the Elf Owl (Micrathene whitneyi) from southern US and Mexico
Largest is the European Eagle Owl (Bubo bubo) from north and west Europe

Most species of owl are protected by law but many are threatened with habitat destruction and through the use of pesticides. Some species are critically endangered.

GENERAL ADAPTATIONS OF OWLS

EYESIGHT

Owls cannot see in complete darkness. They do need light to enable their eyes to work, but at much lower levels than us. On the retina (back surface of the eye) owls mostly have rods (compared to cones of Diurnal Raptors) which enable them to see in darkness. They do not have very good colour vision as the cones are responsible for this (diurnal owls do have some colour vision but their night vision is reduced). The retina of owl is very large compared to other birds. A rod is nearly the size of three cones and therefore the larger surface area is for more rods to be placed there.

As the eye is so large it cannot be moved within its socket in the same way our eyes work. As an owl's visual field is approximately the same as ours they have to have a very flexible neck to turn the head to see behind. They can turn just over 180^o from the front (they cannot keep going round and round as some children think they can!- the head would fall off!)

HEARING

As the owls are usually nocturnal they have evolved to use their hearing to locate their prey. Their ears are located behind their eyes and are offset. Therefore sounds reach the ears at slightly different times and they can pinpoint prey.

The facial disk possessed by owls allow them to funnel sounds into their ears the same as our outer ear. The Great Grey Owl has an extremely large facial disc to funnel sounds of lemmings into its ears. In the winter it can manage to hear lemmings up to 12 inches under the snow. Barn Owls also have large facial discs to help them locate prey while they are flying.

SILENT FLIGHT

The silent flight of owls is obtained partly through plumage and partly through specially designed wing feathers. The body feathers are very soft to smooth the flow of air and on the outside edge of the primary feathers (longest wing feathers) they have a serated edge which are known as barbs. These again help the air to pass though more easily and reduce friction and therefore noise.

FEET AND CLAWS

Like diurnal raptors owls have powerful feet to catch and hold onto their prey. Scientifically the black curved parts at the end of the toe are called 'claws' on an owl (compared with talons on a diurnal raptor).

Owl References:

Konig C., Weick F. and Becking J. (1999) Owls: A Guide to Owls of the World. Pic Press, Sussex

LINK: Owl Pages: A good site on all Owl species and detailed information about them.