What is a Barn Owl?

The barn owl (Tyto alba) is one of the most distinctive birds of prey in the world. It is also one of the most widely distributed birds in the world, being found in almost every corner of the globe (excluding some very desert or isolated places). It has a much loved heart-shaped face, mottled buff back and ghostly white front and underside. It belongs to the Tytonidae group of owls, a group separated from the more numerous Strigidae – the typically woodland owls. The barn owl tends towards open countryside, such as farmland and meadows, where it can fly silently and unobstructed, listening out for small scampering animals that make up the majority of its prey.

Like most owls they are nocturnal, relying on their incredibly acute sense of hearing to detect their prey. Both their ears are hidden underneath feathers, they are different sizes and are not symmetrically placed on the side of the head. The feathers covering the face act like funnels, directing sound towards the ears, allowing the owl to hear in exquisite detail. It is said that a barn owl can hear a mouse’s heart beating up to 30ft away, so it is easy to imagine how loud a mouse running is across a field!

Whilst a barn owl’s favourite meal in Europe appears to be voles, they will gladly take shrews, mice, bats, lizards, amphibians and even insects such as grasshoppers will be taken. The prey is generally swallowed whole or in very large chunks. The bones (or parts of the exoskeleton) are indigestible and so remain in the pellets, making it easy to observe what the barn owls have been feeding on.

Common Myths… Busted!

It is a common thought that all owls are wise – even in children’s TV, remember “Owl” from Winnie the Pooh? This myth stems from Greek mythology, where Athena, the goddess of wisdom, had a pet owl. People presumed that because she was wise, owls must be too, right? Wrong. They have a skull the size of a tennis ball, and a brain weighing only a few grams! That’s not to say they’re not good at what they do, they boast an exceptionally high hunt success rate – way higher than that of most birds of prey. They’re just terrible at learning, compared to crows, who are exceptionally smart.

How are Barn Owls Protected? 

As with all birds, the Wildlife and Countryside Act 1981 protects the eggs and nests of the barn owl. They are listed under Schedule 1 of the amended version of the Act, which makes it illegal to:

• Kill, injure of take (catch/capture or have in one’s possession) a barn owl
• Take, damage or destroy the nest of a barn owl, whilst the nest is in use or being built
• Take or destroy a barn owl egg
• Have in one’s possession or control a wild barn owl (dead or alive) or egg
• Intentionally or recklessly disturb any dependent young of wild barn owls

Signs of Barn Owls

If a site that is to be modified or built on has large trees that may be capable of housing a barn owl, and evidence of owls has been found, it might be necessary to conduct a barn owl survey.

There are several signs that could be found whilst surveying that would be indicative of a barn owl presence:

Pellets

Contrary to some beliefs, the pellets are not droppings, instead they are regurgitated by the owl as a way of clearing their stomach of the indigestible bits of their dinner. This is primarily hair, bone and insect exoskeletons. The pellets are distinguishable from those of other species when they are fresh, as they are the only known pellet that is black when fresh, slowly turning grey over time. Other species such as kestrel, little owl and buzzard all produce grey pellets.

Droppings

This is a slightly harder sign to distinguish, as barn owl droppings are white, watery ‘splashes’ (if they land on the floor) or ‘streaks’ (if they… slide… down a wall), sometimes with small black parts. Basically, they are the same as most other birds droppings! Usually they will be found under suitable roosting or perching places, such as branches and beams. As they are hard to distinguish, they cannot be used solely to determine barn owl presence, and will often be found with other signs.

Feathers

Needless to say, finding barn owl feathers is (bizarrely…) indicative that a barn owl was once there. With a trained eye it is possible to determine whether they are male or female, and whether they are adult or nestling feathers.

Nest/Roost Debris

There is an important distinction to make here between nest debris and roost debris. Where a barn owl only roosts, the pellets will have time to age and dry without being disturbed, and will still look like pellets. In contrast, in a nest, the pellets will be continually walked on whilst they are still soft, resulting in a compacted layer that will solidify into a mass without many individually distinguishable pellets.

Along with the pellets, there is likely to be nesting materials – grasses and soft vegetation, perhaps even some un-eaten small mammals and insects that are left there as a cache for when hunting becomes harder in winter months.

  Barn Owl Tree Roost Site

Suitable Nest Sites

Barn owls tend to nest away from dense human populations, frequenting barns and other agricultural buildings that are near to open rough grassland or river banks. Alternatively, and more naturally, they will nest in suitable mature trees – anything from a standalone tree in the middle of a field to a mature tree forming part of a hedgerow or woodland edge.

The trunk diameter of trees at about chest height is a good way to estimate the age of the tree and the likelihood of a barn owl using it as a nest. The guidance for barn owl survey methodology lists the common trees as such; in ash, sycamore and willow trees, 0.5m diameter is considered noteworthy. In horse chestnut and beech the diameter only becomes ‘interesting’ when it reaches 0.75m, and in oak trees it must be 1.5m diameter! These figures are only guidelines however, and are not strict rules.

Activity Surveys

In order to categorically state whether a barn owl is using one of the suitable nest sites, it must be ascertained whether the suitable trees and buildings are a Potential Nest Site, or an Active Roost Site.

Potential Nest Site

The suitable sized trees as mentioned earlier are closely inspected to see if they have a big enough crack or hole (that tend to naturally appear with age) for a barn owl nest. The hole or crack must be at least 80mm wide, with a “floor” area of about 250cm x 250cm. Again, these are only guidelines, and therefore common sense plays a part in determining a Potential Nest Site.

Active Roost Site

These are not nest sites, i.e. the owls do not breed at these sites. These will be marked with those features mentioned previously – splashes or streaks of droppings, pellets and feathers. The chances of finding an Active Roost Site are much higher than finding a Potential Nest Site, as each owl will have several roost sites compared to one of two nest sites.

Active Roost Sites can be found in any place where the owl may stop to feed or to rest. Tending towards the same habitat of open grassland or woodland edges, the roost sites could include branches, beams, machinery and roofs, just about anywhere an owl can land and feel safe.

The signs that indicate an Active Roost Site can be used to estimate how active the site is, whether it is regularly or occasionally used. Additionally, we can estimate when the site was last used, usually categorised as up to three years ago, or greater than 3 years ago. It is rare that this level of information is required for a barn owl survey, however.

If an Active Roost Site is found with only occasional pellets and feathers is indicative of a rarely used Active Roost Site, and may be classified as a Temporary Rest Site, though this level of distinction is rarely needed.

Barn Owls are Present!

Contrary to popular belief, finding a barn owl (or any other protected species) on a proposed development site is not the end of the world, nor is it always a huge financial drain. If a barn owl is found on your site, the likelihood is that only alteration will be when you can conduct the work, and perhaps adding in a barn owl box, to keep the owls happy once you’ve done your work, but the ecologist will guide you through this and make it painless and easy. Simple!

Photo used with permission from Gerry Gutteridge.

Ben Jones