How many Barn Owls did there used to be in the UK?
- The first reliable UK population estimate – 4,000 pairs (±c. 30%) – came from Project Barn Owl conducted between 1995 and 1997.
- Surveys by Blaker (1932) and Shawyer (1987) were great achievements in their day but do not meet modern scientific standards.
- Evidence for the species’ historical decline in Britain, although overwhelming, is largely anecdotal.
- The often-quoted figure of a 70% decline in England and Wales between the 1930s and 1980s cannot be relied upon.
- Since 1995-97 no reliable population estimates have been made.
Between 1995-97 and 2009 the number of Barn Owl sightings recorded by the BTO Breeding Bird Survey (BBS) increased dramatically – strongly suggesting a population increase. However, after 2009 BBS recorded a 63% decline in Barn Owl sightings. Unfortunately BBS is only a daytime bird survey so its reliability as an index of Barn Owl abundance is debatable, particularly as an increase in Barn Owl sightings by day is usually a sign that the birds are struggling to find enough food.
An entirely separate project, the Barn Owl Monitoring Program, recorded a 50% drop in the number of nests in the period 2000 to 2009 but this figure is also thought to be unrepresentative. It is possible that by 2009 the UK Barn Owl population reached significantly more than c. 4,000 pairs – no one will ever know for sure. Population estimates produced since 2000 are not reliable. Why therefore, is Barn Owl no longer an Amber-listed species?
At European level, the Barn Owl is still listed as a bird of ‘Conservation Concern’ in Birdlife International (2017) European Birds of Conservation Concern. Whilst here in the UK, in 2015, the Barn Owl was moved from the Amber List in Birds of Conservation Concern 4 to the Green List suggesting a reduction in concern. However, the species move to the Green List was not made because of any change in the UK population level but simply because an updated European Birds of Conservation Concern (SPEC) list was not available at the time.
Why were Barn Owls more common in the distant past?
- There is a strong consensus that Barn Owls must have been a lot more common before agricultural mechanisation.
- Farming was very much less intensive and overall, wildlife was much more abundant.
- Small mammals would have been much more common when there were more hedgerows, more marginal grazing land, and pasture was mainly permanent, “unimproved”, and much less intensively grazed.
- Stored cereal crops, in ricks or barns, became so infested with mice and rats that some enlightened farmers encouraged Barn Owls into their buildings via special access holes or “owl windows”.
- There was no fast traffic or overhead wires for Barn Owls to fly into and no poisons in the food chain.
It’s quite likely that Barn Owl decline started in the mid-1800s as a result of persecution by gamekeepers, egg collectors, and birds shot for taxidermy. The fact is we shall never know to what extent these activities might have affected the Barn Owl population. Indeed they may have only caused the temporary suppression of local population levels.
In the late 1800s and early 1900s increasing human population levels and the proliferation of mechanised farming led to an increase in the intensity of land management, resulting in the loss of Barn Owl habitat. This accelerated during WWI and again in WWII, with a drive for Britain to become more self-sufficient. The idea that British farmers had a duty to produce as much food as possible became deeply ingrained during WWII, and a system of government grants that paid farmers to destroy wildlife-rich fields and hedges, continued right up to the 1980s. The changes in farming practices, stimulated by the legacy of WWII, human population expansion, government policies, and consumer pressure for ever-cheaper food, are the main reasons behind the Barn Owl’s historical decline in Britain.
Why are they less common now?
There is little doubt that the main factors are;
- Low food availability due to intensive farming.
- Road mortality, especially dispersing juveniles on fast trunk roads.
- Loss of traditional roost/nest sites through conversion or decay.
Other contributory factors may include;
- The effects of secondary poisoning by rodenticides.
- Increased frequency of extreme weather events.
How have extreme weather events affected the UK Barn Owl population?
The winters of 2009/10 and 2010/11 were unusually cold, which no doubt resulted in increased mortality. The following springs were also very cold and unusually dry, which suppressed small mammal activity. This in turn limited Barn Owl breeding success. By the autumn of 2011, Barn Owl numbers had probably been knocked back to around 4,000 pairs, i.e. any increases in the period 2000-09 had probably been wiped out.
The late winter peak in mortality, which occurs every year, normally subsides as temperatures increase in March. However, in 2013 the extremely cold weather experienced through January and February continued throughout March and mortality kept increasing. By mid-April, when temperatures finally increased, most Barn Owls were dead. The few that survived failed to breed or bred late. The average number of breeding pairs in each county was 70% below normal. In some counties, there was no breeding recorded at all. The only exceptions were Cumbria and SW Scotland, where the number of nests was reported to be “low” rather than “disastrous”. Numbers of non-breeding birds are always difficult to gauge, however, there can be little doubt that numbers dropped well below 4,000 pairs (the last reliable estimate). It is possible that there were fewer than 1,000 pairs nesting, nationwide. In May 2013 there were probably fewer Barn Owls in Britain than at any time since records began.
Note: Although the winters of 1947 and 1963 were more extreme, they were affecting a much bigger Barn Owl population.
Prolonged wet spells
Generally speaking, the winter of 2011/12 was not too severe and March 2012 was unusually hot resulting in early egg-laying and above average clutch sizes. By the end of May many nests contained 4-6 young; well above the average of 2.9. In fact, 2012 was all set to be a bumper year for Barn Owls – then it all went horribly wrong. From 8th June onward prolonged rain caused massive nestling mortality, although some pairs did nest successfully later in the year. Overall, 2012 was probably an average year – not the bumper year that was so badly needed.
- December 2009 to January 2010 – worst winter weather (cold/snow) for 30 years.
- December 2010 – coldest December for 100 years.
- First 2 weeks of February 2012 – coldest since 1991.
- March 2012 – hottest March since 1997.
- June 2012 – wettest June in England and Wales since 1766.
- March 2013 – coldest March since 1962.
- July 2013 – hottest July for 7 years.
- December 2013 – worst December floods since 1953.
- January 2014 – the wettest January ever recorded.
- December 2013 to February 2014 – the stormiest (windiest) and wettest winter for 250 years.
- September 2014 – driest September since records began in 1910.
Since 2013 we have been collating Annual Monitoring Data from c.37 independent groups across the UK who between them check about 7,000 potential nest sites every year. We’ve also become increasingly aware of Climate Change, particularly the ‘new normal’ meandering of the Jet Stream caused by Arctic Amplification (the arctic warming 2-3 times faster than the equator). It has become abundantly clear that frequent extreme weather events are having profound effects on Barn Owl survival and nesting success – a trend that looks set to continue. More information is available in the annual ‘State of the UK Barn Owl Population‘ reports.