In the seventies barn owls populations had dropped to their lowest numbers in history. At present, and as a result of protection measures, the barn owl is again an often sighted bird of prey in agricultural landscapes.
Published in: EOS magazine 9, 2009 (in Dutch: Kerkuil maakt comeback – pdf)
European barn owl (Tyto alba) populations were having a hard time in the seventies, not only in Flanders and The Netherlands, where breeding pairs were estimated at only 100. This number was far below the 1000 respectively 1500-3000 breeding pairs that were estimated earlier for Flanders and the Netherlands. Philippe Smets from the Flemish Barn Owl working Group explains that the harsh winter of 1962-63 was to blame in the first place. ‘As a result of freezing temperatures and abundant snow, barn owls couldn’t catch enough mice.’ But agricultural pesticides were also a major culprit, especially the heavily used insecticide DDT. In Western Europe the barn owl population had dropped to only 10% of its original numbers. The development of industrial agriculture, where the agricultural landscape – favorite hunting ground for barn owls – completely changed, was another unfortunate event that added to the decreased availability of prey species.
‘But of equal importance in the decline of the barn owl was the lack of suitable breeding locations,’ explains Smets. ‘Openings to church and barn attics had been locked as to prevent wild pigeons from entering. As a result, more and more barn owl couples didn’t find a suitable nesting location to raise their young.’
The importance of nest boxes
In Flanders and The Netherlands Barn Owl Working Groups were founded about 30 years ago. Their major effort was to install nest boxes in church towers, farms and barns. Each year, volunteers checked the nest boxes for young and provided them with a ring. This resulted in detailed data on breeding success. ‘Today the barn owl has largely recovered’, says Smets. ‘In 2007, we counted 964 breeding pairs, that altogether raised 4000 young in Flanders. 2008 resulted in a lower reproduction output with 742 young, probably as a result of a harsh winter and wet spring. We found that 80% of barn owls used a nest boxe to raise their young, thereby showing the importance of the protection measures by the Barn Owl Working Group. With 3000 breeding pairs the future looks bright for Dutch barn owls too.’
The barn owl is on its return, but new dangers have been identified. Currently, traffic mortality is the highest cause of death in barn owls. ‘In 2008, 180 barn owls were killed by traffic in Flanders, which is three times as much as in 2007. The increase is attributed to poor food conditions that year, leading to more barn owls hunting along roads outside their territory. If large numbers of barn owls get caught by traffic, this may eventually stop population growth,’ explains Smets. ‘Another major threat is the abduction of barn owl young for pet keeping,’ explains Jan Rodts from Bird Protection Flanders. ‘By providing the young with a false ring it looks as if they were legally born from captive barn owl parents.‘
EXTRA: Birds of prey recovering from poisoning
The barn owl was not the only bird of prey suffering from the toxic effects of DDT and other pesticides. In 1962, American biologist Rachel Carson described in her book Silent Spring the decline of wild bird populations after exposure to DDT. DDT caused egg shell thinning, and led to broken eggs and embryo mortality. Birds of prey were especially vulnerable due to their position on top of the food chain, as a result of which they accumulate very high concentrations of pesticides and other toxic compounds. The peregrine falcon (Falco peregrinus) was the biggest loser in this story. Between 1950 and 1974, peregrine falcon populations had dropped with almost 90% in both Europe and North America. This decline was exclusively attributed to the use of DDT and other toxic pesticides. In the 60s, the peregrine falcon was completely extinct in Belgium. Only after establishing a regulation for the use of DDT and other pesticides could populations recover. In Belgium the Fund for the Protection of birds of prey (FIR) helped the peregrine falcon by installing nest boxes on cooling towers from nuclear installations, electricity pylons, and other high buildings, such as cathedrals.
As a result, in 2008 in Flanders counted 35 breeding pairs and 78 young. Other birds of prey that had suffered from pesticide usage – such as buzzard, sparrow hawk and kestrel – also recovered. ‘But caution is needed, especially since hunters shoot or poison birds of prey because they believe them to be competitors for game meat,’ says Jan Rodts.