August 4th is International Owl Awareness Day, so what better bird of the month for August than the barn owl? One of five species of owl in the UK, the barn owl is paradoxically both instantly recognisable and yet rarely seen by most of us. Once encountered, though, they are never forgotten. Their ghostly, silent flight, seen across a field at dusk or glimpsed in car headlights, only adds to their air of mystery.
The Ghost Bird
Barn owls have a very distinctive appearance. White underparts and face combine with buff wings and back. This buff area has varying levels of grey and white mixed in to give a subtle mottled effect. Despite not being completely white, in low light this is the overwhelming impression. In fact, their scientific name, Tyto alba translates as ‘white night owl’, which is a good description. Males and females are almost impossible to tell apart.
Short, stiff feathers surround their heart-shaped faces, making a disc of the face which acts like a reflector to direct sounds to their asymmetric ears. The asymmetry helps them pinpoint their prey easily by sound. This is a huge advantage for a mostly nocturnal species, although birds in the UK will hunt in the daytime much more than their overseas counterparts. Large, dark, forward-facing eyes complete the appearance. Although they predominantly use sound for hunting, they also have excellent eyesight, particularly useful for finding prey at dusk or at night.
Traditionally, humans have labelled owls as one of the wisest birds, probably due to their front-facing, flat faces. These make them look more human than many other birds. Sadly, we now know that they are not in the same league as corvids and other birds with problem-solving skills. This is because they use so much of the brain for processing the information they receive from their excellent sight and hearing, leaving not as much left for other cognitive activities.
A Bird of Farm and Field
In the UK, while tawny and long-eared owls are woodland birds, barn owls are predominantly birds of open, lowland countryside. This is often farmland, but can be heath, saltmarsh or even golf courses! Their ideal habitat is open grassland with plenty of small mammals, hunting perches and roosting opportunities nearby. They are often seen quartering over fields or working their way along field margins, listening for vole movements in the grass. Because of their long legs, they are not restricted to short turf and can reach into quite thick vegetation.
As their name suggests, they often use disused barns and other farm buildings to rear their young, as long as these are undisturbed. They also nest in tree holes and will use artificial nest boxes. For a reasonably large bird, they lay quite big clutches. These can be between four and seven eggs, although up to eleven is possible. Females lay them at intervals, with the last chick to hatch often not surviving long in years with low vole numbers.
The survival rate for chicks generally is low with approximately 75% of young not making it through their first year. This makes larger clutches a good strategy, increasing the chance of some young making it to adulthood. Life expectancy beyond that is low too, with most not living beyond three years, although the European record is a bird of 21.
A Life of Challenges
Being a barn owl is not easy, despite the brilliant evolutionary adaptations that help them hunt. In the mid-twentieth century the use of chemicals such as DDT in the countryside almost certainly affected them adversely. These pesticides become more concentrated in birds and animals higher up the food chain, as famously documented in Rachel Carson’s 1962 book Silent Spring. One of the consequences was that predatory birds (including peregrine falcons and barn owls) became infertile or produced eggs with shells that were too thin and easily crushed in the nest.
Carson’s book ultimately led to DDT being banned and, in the UK, affected species have recovered to some extent. However, the challenges for barn owls are not over. While natural fluctuations in prey populations mean they will always have good and bad breeding years, bad weather affects their ability to hunt. A warming climate may bring increased periods of rain and wind to the UK. Both make it difficult for barn owls to hunt by impeding their ability to hear prey.
One of the biggest causes of death, though, is traffic collisions. Because they hunt at low heights and often swoop over roads, they are frequently hit by vehicles. The Barn Owl Trust estimates that cars kill approximately 4,000 barn owls each year, many of them youngsters moving to find territories of their own. The vast majority of these deaths occur on major roads. A straightforward mitigation measure is to install a screen of trees on either side of roads to force the owls to fly higher and avoid collisions. Making verges less attractive for hunting by letting scrub grow would also help.
Owls Overseas
The barn owl is globally the most widespread owl and is also one of the most widely distributed of all bird species. It lives on all continents except Antarctica. This has inevitably led to some diversification and variation in appearance across its range. Some of the estimated 28 subspecies are much darker than in the UK and even have brown faces. There are also some behavioural differences, with some barn owls overseas being forest-dwellers rather than birds of open habitat. These differences between populations have led some scientists to believe that a few of the subspecies have split to full species level.
The Demon Owl
If you are anywhere with suitable habitat, look out for this charismatic and ghostly bird. But don’t expect to hear one making a cliched owl hooting sound. If this owl makes any noise at all it is a horrible mixture of shrieks and hissing. Which probably explains one of its nicknames, the demon owl! Far from demonic, though, this is a beautiful species and surely one of many people’s favourite birds