Dave Leech

The Barn Owl must surely be one of the most iconic and well-loved bird species in the UK.  While it is actually one of the most widespread species globally, occurring on all continents except Antarctica and occupying a surprising range of habitats, in the UK it has particularly strong associations with agricultural land and has become a symbol of the conservation issues facing farmland birds in this country. 

The first national Barn Owl survey, indeed the first national survey of any bird species, was carried out by George Blaker in 1932.  Blaker estimated that there were approximately 12,000 pairs of Barn Owls in the UK, although he noted that the species already appeared to have been in decline during the 30 or 40 years prior to his survey.  Surveys conducted over the next 50 years identified a continued decline in numbers and by the time of the Hawk Trust survey in 1982-85, the population was thought to have fallen to just 4,450 breeding pairs. 

This decline, along with that of many other farmland bird species, has been linked to the intensification of agricultural practices in the UK during the 20th century.  Areas of grassland and rough pasture in which the favoured prey of Barn Owls, the Field Vole, thrive had become less and less abundant, as had the old trees and barns in which owls find cavities to nest.  The increasing use of organochlorine pesticides such as DDT, which caused thinning of eggshells and led to the eggs breaking in the nest during incubation, further worsened the situation and the future looked increasingly bleak.

However, the use of DDT and related compound was banned in the UK in the 1970s and since then, and conservationists have attempted to implement other measures, including the provision of nestboxes and development of more Barn Owl-friendly agricultural policies.  In 1995, the BTO joined forces with the Hawk & Owl Trust to conduct Project Barn Owl, which produced a population estimate of approximately 4,000 pairs, suggesting that the decline might have started to level off.  What was really needed, however, was a system of monitoring the species on an annual basis.  Compared to many birds, Barn Owls are an awkward species to monitor – they are nocturnal, they occur in relatively low densities and they do not sing.  It was therefore necessary to develop a specialist survey for the species, and thus, in 2000, the BTO’s Barn Owl Monitoring Programme (BOMP), funded by The Sheepdrove Trust, was born. 

Each year since 2000, volunteer observers holding the required Schedule 1 Licences have visited a national network of potential Barn Owl nesting sites, the majority of them nestboxes, recording whether owls are present and if so, whether they are attempting to breed.  During the first two years of the project, The Wildlife Conservation Partnership monitored 200 sites in England.  Since 2002, this total has been supplemented by an extra 300-400 sites monitored each year throughout the whole of the UK as part of the BOMP Network, and the number continues to rise.  On average, 62% of sites contain breeding owls, but this figure varies from 50-80% depending on both the abundance of voles and weather conditions during the previous winter.

Observers visit the sites on several occasions, and each time they record what’s actually in the nest, counting the numbers of eggs of chicks that they find in the same way that participants in the BTO’s Nest Record Scheme (www.bto.org/goto/nrs.htm) do.  As well as being used to calculate clutch and brood sizes, the data collected can tell us when the eggs were laid and the proportion of nests that successfully produce fledged offspring.  The measures of productivity may also vary between years as food availability and weather conditions fluctuate.  They may also vary between habitats, with rough grassland providing better feeding habitat than arable or pastoral areas, resulting in larger average brood sizes.

BOMP may only be six years old, but it has already proved to be one of our most popular recording schemes and has provided a sound foundation on which we can build the future of Barn Owl monitoring in the UK.  We’re very grateful to the network of observers and landowners for all the time and energy they put into keeping an eye on the fortunes of this amazing species. If you’d like to know more about the project, please visit the website at www.bto.org/goto/bomp.htm.