Barn owls are unquestionably one of the most instantly recognisable birds in Britain and were once a common sight in our countryside. In recent years the Barn owl has suffered a decline in numbers to the point that seeing one is an increasingly rare privilege. Habitat loss, increasing volumes of road traffic and the use of rodenticide poisons to reduce populations of rats and mice on which they feed are considered the main causes behind the Barn owl’s decline, although climate change may also be having a detrimental impact. Encouragingly, 2017 appears to have been a good year for the species and many landowners are now much more aware of the needs of this species, so hopefully this is a positive sign.
That which follows is a summary of Barn owl natural history. The detailed article for this species will follow in due course.
The Barn owl at a glance
At least 31 subspecies proposed, based largely on colouration, but DNA data imply only 10 valid; type subspecies, Tyto alba alba, found in UK.
Size: Smaller than many people imagine, standing 34cm (1 ft) tall and weighing 250-480g (0.5-1 lb.). No apparent sexual difference in size, although females generally heavier than males. Wingspan of 90-98cm (3 ft).
Colour/Appearance: Unmistakable white, heart-shaped face with tan/buff back and wing tops; pure white or speckled underneath.
Distribution: Fairly wide distribution in UK, although has suffered significant declines during the past 50 years. Absent from much of central and southern Scotland as well as northern-most Scotland and Scottish Islands. Absent from north-west Ireland. RSPB estimate UK wintering population to be 12,500 to 25,000 birds, with 3,000 to 5,000 breeding pairs.
Longevity: Typically 1 to 3 yrs, although 21 yrs recorded from captivity.
Sexing: No significant difference in size, but the vast majority (~98%) of males have pure white breast, while females chest is flecked with black dots; juvenile females heavily flecked, fading with age.
Activity: Hunt nocturnally (best time to see them is dawn/dusk), but may be active during the daytime especially when feeding young. Often found sitting in trees during the day. Predominantly sedentary bird in Britain but may migrate considerable distances according to prey distributions.
Territory/Habitat: Most often bird of open country, hunting along field edges and ‘quartering’ larger fields (flying low and covering area in sections). Preference for grassy headlands and fields with un-tended edges and hedges (with fence posts for perching). Also found along riverbanks and may hunt along roadside verges, where they’re susceptible to traffic. Not uncommon near urban areas. Generally resident, but will migrate substantial distances (500km / 340 mi.) if food becomes scarce. Generally chooses secluded areas (e.g. barns, abandoned buildings, ruins etc.), especially for nest sites. May be found in cliff holes, mines and holes in trees. Take readily to nest boxes. Arguably impossible to estimate territory accurately, but some suggest 4-5 sq-km (2 sq-mi.) required to support a pair.
Diet: Short-tailed voles significant prey, along with wood mice and brown rats (overall 90% diet is rodents). May take shrews. Report from Sussex during 1985 of owl killed by dog as it tried to attack one of its puppies (presumably aberrant behaviour). Food swallowed whole and indigestible parts regurgitated as pellet.
Reproduction: Typically monogamous (life-pair), although not always. Productivity linked to small mammal (prey) populations. Breeding condition reached at 350-425g (12-15 oz.) and breeding season runs March-August, with older birds breeding earlier. Copulation occurs after food presentation; may also engage in mutual preening to strengthen pair-bond. Egg laying date affected by habitat quality (food availability); starts late March/early April in good vole habitat (e.g. young conifer stands), while more likely during May/June in arable farmland. Most eggs laid April/May. Four to seven white eggs (up to 15 in good vole years) laid over several days (about two days between laying). Female incubates alone, fed by male who brings in an average of 9 items per day during incubation, increasing once young have hatched. Eggs incubated for around 30 days and hatch at two-day intervals (different aged birds in nest at same time). Eyes open at 8-11 days and skeletal growth complete (can walk) by 5 or 6 weeks old. Wing growth complete and birds fledged at 8-10 weeks old. High mortality (up to 75%) during first year.
Behaviour and Sociality: Lives singly or in pairs and hunts alone. Various different call types; long, harsh ‘chrrrrreeh’ call made while perched and long-drawn ‘rushing’ sounds during aggressive encounters.
Threats: Significant population declines across much of Europe and North America associated with numerous factors, including changes to farming practices. Susceptible to traffic while hunting road verges and agricultural rodenticides. Hit hard by prolonged bad weather (esp. heavy rain and snow), may fall prey to peregrines and goshawks and may suffer kleptoparasitism (food-stealing) by kestrels.
Bibliography
Nick Baker’s British Wildlife: A month by month guide - by Nick Baker
New Holland Publishers
-- 2003
-- ISBN: 978-1845171131
Silent Fields: The long decline of a nation’s wildlife - by Roger Lovegrove
Oxford Univesrity Press
-- 2007
-- ISBN: 978-0199548156
Simon King’s Wildguide - by Simon King
BBC Books
-- 1994
-- ISBN: 978-0563364962
The Darkness is Light Enough: The field journal of a night naturalist - by Chris Ferris
Sphere Books Ltd.
-- 1986
-- ISBN: 978-0718126902
Wild Animals of Britain & Europe - by Helga Hofmann
HarperCollins Publishers
-- 1995
-- ISBN: 978-0007627271