Barn Owl Ecology
Barn Owls were once stated to be the most widely distributed land bird in the world, but sub-classification now restricts UK Barn Owl subspecies (Tyto alba alba) distribution to southern and western Europe, stretching to north Africa.
It is estimated that there are 4,000 Barn Owl pairs in the UK (Toms et al. 2000) but there is an absence of more recent data. Various threats such as indirect exposure of rodenticides through ingested prey have decreased over recent years but can still remain a problem, as well as loss of prey rich habitat and nesting cavities. Prolonged, severe winter weather conditions and major, un-screened roads with suitable verges for hunting also present a significant threat to Barn Owls, and are the major causes of mortality for this species, especially dispersing juveniles.
Barn Owls have very distinct colouring in comparison to other UK owl species, with white underparts and golden backs; it is thought that their backs provide them with camouflage from above, while their white underparts work as an anti-silhouette strategy from below.
Across their preferred habitat of open rough grassland, they are well adapted to hunting mice, voles and shrews, with a light body weight and large wings with comb like fringed edges, enabling them to fly slow and silently. Their heart shaped face acts as a disc allowing them to focus sound, while their long legs help them to catch their prey through long grass.
It is not easy to sex a Barn Owl when seen in flight, but at closer inspection males tend to be lighter across the buff areas and the females have visible black spotting across the chest and under wing.
(C) James Wainscoat
Barn Owls don't call often, but in circumstances such as courtship or in response to a threat they can screech, hiss or make a snoring/purring sound. As a nocturnal species, Barn Owls are seen at night but often begin to be active at dusk and cease their activities at dawn. However, inclement weather can stop Barn Owls from hunting successfully, so they may be seen foraging during the day if conditions have hindered nocturnal hunting opportunities.
Courtship begins over Winter and by early Spring pairs are spending much of their time at their nesting site. The male and female will cement their bond by cheek rubbing and preening, while the male increases his hunting excursions to feed the female to increase her weight, ready to breed with her. On average, Barn Owls lay between 4 - 6 eggs on a base of regurgitated pellets, laid over an 8 - 21 day period; incubation begins when the first egg is laid (unlike many other bird species which start incubation when all eggs have been produced), therefore each egg in the clutch hatch at different stages, known as 'asynchronous' hatching.
The breeding season distribution of Barn Owls in Britain and Ireland as shown in the BTO Bird Atlas 2007-2011
After around 30 days of incubation by the female, eggs will hatch within 2 -3 days of one another, with the aim of extending food supply requirements over a longer period of time. There can often be a 3 week age difference between the youngest and oldest chick. By 8 - 9 weeks Barn Owls have attempted their first flight and by 10 to 11 weeks old many owlets will now look like adults and will be attempting to hunt for themselves.
Once fledged, juvenile Barn Owls will look to disperse from the natal site, with distances varying depending on food supply, roost opportunity and the presence of a prospective mate. Once a suitable area for roosting, hunting and breeding is found, this home range can vary in size from 350ha up to 5,000ha, and often overlap with neighbouring Barn Owls; an increase in food supply will usually contract the size of a home range.