The Barn Owl

Description

The Barn Owl Tyto alba is a much loved British bird with its distinctive white heart shaped facial disc and its predominately white breast/under parts in contrast to the plumage of the head, upper body and wings which are a golden buff colour delicately marked with black specks and silvery grey mottling. The soft feathers and comb like fringe along the leading edge of the outer main primary wing feathers give the owl its silent flight. The female tends to be darker in colour above with variable black spotting down breast and under wing whereas the male is lighter with little or no spotting down breast.

Their size ranges between 33cm to 39 cm with a wing span of 85cm to 93cm. They weigh between 280g and 350g, the female being slightly larger and heavier than the male.

Voice

A long drawn out blood-curdling screech particularly when in flight but also hisses and chirrups. The female will sometimes snore when begging for food from the male which is also a characteristic of the young at the nest site. The adult owls become more vocal during the breeding season.

Hearing

Barn Owls are mainly nocturnal and hunt predominatly by sound. They have an acute sense of hearing and can detect the slightest movement and sound of their prey. The ear openings are situated inside the facial disc just behind the eyes and are set asymmetrically, meaning one ear is slightly higher than the other. The facial disc acts as a sound funnel, collecting and filtering sound. This allows the owl to detect the movement of its prey with complete accuracy.

Vision

The Barn Owl has small button like black eyes which are forward facing. The forward facing aspect of the eyes gives it binocular vision (seeing an object with both eyes at the same time) and enables the owl to judge the distance of its prey more accurately. The eyes are fixed in their sockets thus limiting peripheral vision but to compensate for this the owl can rotate its head through 270 degrees. As the owl is predominately nocturnal the retina in the eye is extremely sensitive to light allowing it to see when hunting in very low light levels.

Breeding

The Barn Owl normally begins courtship in February or March in the UK. The first egg is usually laid in late April or early May but this can vary according to weather conditions and the availability of food. The Barn Owl will choose one of its many roosting places as its breeding site which may be in an old barn, a bale stack, a tree hole or a purpose built nesting box. The female will usually lay between 4 and 6 white eggs but this could be higher if prey is abundant. The eggs are laid at intervals of two to three days. Incubation lasts 30 to 31 days but the female begins when the first egg is laid therefore the young will hatch at two to three day intervals. The young owls are able to fly short distances at around 55 days old and become fully fledged at about 67 days. After a further 1 to 2 weeks the young owls will usually leave the nest site permanently. Second broods can occur when food is in great abundance.

Records show that the survival rate for juvenile Barn Owls in their first year is only about 30% - most will have unfortunately died through the winter months due to starvation because of their inexperience in hunting in winter conditions plus the reduction in small mammal prey at this time of the year.

Habitat

Open country or farmland with rough tussocky grassland, typically along field margins, ditches, woodland edge, young plantations where a high density of small mammals can be supported.

Food

Mainly small mammals such as short- tailed field vole, common shrew, bank vole, wood mouse and young rats. The shot-tailed field vole constituting the most popular of prey items amounting to over 50%. Occasionally small birds will also be taken as prey.

Hunting

The Barn Owl hunts mainly by night but can be seen before dusk and around dawn particularly during the breeding season when feeding young. They can sometimes be seen in the daytime when continuous rain the previous night has prevented them from hunting and also during winter months when there is less prey. Using its acute sense of hearing, night vision and silent flight the owl will float moth-like over the tussocky grass margins beside hedgerows, along ditches and around woodland edges hunting for unsuspecting small mammal prey.

Once the prey has been detected the owl will hover momentarily then swoop down stretching its legs and talons forward into the long grass and onto its prey. The prey is normally swallowed whole or taken directly back to the nest site to feed the young owlets.

Prior to hunting the Barn Owl will normally regurgitate a large smooth blackish pellet which contains the indigestible parts such as bones, teeth and fur etc from previously consumed prey. Pellet analysis can be helpful in determining the owl’s diet and also what small mammals exist within the owls hunting range which would typically be around 3km² in the breeding season.

Decline

National surveys showed that in 1932 there were 240 pairs of Barn Owls in Cheshire but only 35 pairs were recorded in a 1982 – 1985 survey (Shawyer 1987) This is a staggering 85% decline over 50 yrs which is more than the 69% recorded nationally.

The decline can be attributed to several reasons:

• Loss of suitable habitat as a result of land development and modern farming practices

• Loss of suitable nest and roost sites, through felling of mature trees and conversion of farm buildings

• Changes in weather patterns

• The construction of major new road networks not only fragmented habitat but also enabled traffic to travel faster, resulting in more road deaths. (Road deaths account for approx 50% of all recorded Barn Owl deaths)

• The use of rodenticides leading to secondary poisoning. Monitoring of Barn owl carcasses by the Predatory Bird Monitoring Scheme shows 91% of owls contain rodenticides (PBMS, 2019).

Since the formation of the Barn Owl conservation groups in Cheshire and Wirral, the downward trend has now been reversed with our best breeding year being in 2007 where 151 known breeding sites were recorded in Cheshire & Wirral. Significant fluctuation can occur in the breeding numbers depending on the cyclic nature of the small mammal population which normally occurs over a 3 to 4 year period.

The aim of the groups has been to increase and preserve the Barn Owl population in Cheshire and Wirral by working with landowners and interested members of the local community by encouraging and creating habitat improvement with wildlife corridors, erection of nesting boxes and by promoting the general awareness to the plight of the Barn Owl.