Chapter 9 of 23

Home Ranges, Roosts and Habitat

Where Barn Owls live, and what they need to stay there

About 6 minute read

A home range, not a territory

Many people picture a Barn Owl as a bird that guards a patch of countryside and chases away rivals. In truth it is a much more relaxed neighbour. Barn Owls do not defend territories. Their home ranges are simply too big to guard, and they overlap a great deal. Watchers have seen owls from neighbouring nests hunting a couple of hundred metres apart, aware of each other and quite unbothered. The only time a Barn Owl really loses its cool is when a strange male walks into the actual nest site, and that seems to be about protecting the mate and not the land.

And what big home ranges they are. It is easy to assume that a bird you always see in the same field never goes anywhere else, but tracking studies show that is not the case. During the nesting season, most of a pair's hunting takes place within a kilometre or two of the nest, in an area of a few hundred hectares. The nest is rarely in the middle of the range. Away from the nest, in winter, owls may commute three or four kilometres to hunt and sometimes even further. In a Suffolk study, several neighbouring farmers each proudly described the resident Barn Owl on their own land, and it took radio tags to show that they were all talking about the same bird.

Sticking with what you know

Barn Owls are homebodies. Once an adult has settled, it will often live its whole life within a single home range, using the same nest and the same roosts year after year. In one long study in Scotland, almost every male nested in the same place from one year to the next, and the females were not much different. Birds that did move usually did so after losing a mate, and nearly always to a site nearby. A pair will also stay together for as long as both are alive.

There is good sense in this. An owl that knows its patch knows where the voles are, where the good posts are, where the wind drops, and which routes are safe on a dark, foggy night. It may even keep a kind of mental map of sounds. A bird that has to start again in a completely unfamiliar landscape wastes a lot of energy, and for an animal that cannot store fat, that can be fatal. It is also why an adult that has been in care after an injury is best released back where it came from.

Roosts

A Barn Owl needs two kinds of home. A roost is a place to rest during the day, and a nest is a place to raise a family. Often they are the same place, but they do not have to be. In a typical range, a bird will use one nest site, between one and four regular day roosts and a few odd corners for nights out, and most pairs roost apart from each other for much of the year. As the breeding season nears, the female moves into the nest site first, and the male follows, and by ten days before laying, they are usually together.

A good roost is high, dry, quiet and out of the wind, with an easy way in and out that leads to open country. It is usually at least three metres off the ground. Barn Owls use farm buildings, church towers, old ruins, hollow trees, quarries, cliffs and occasionally mine shafts. They often tuck themselves between straw bales, which is a wonderful bit of insulation. They will also use dense trees, especially young birds and especially in dry weather, though they seem to be happier in a building or a hollow tree in the long run.

In Britain there is a clear east to west divide. In the west, nearly all nests are in buildings, because there are not many trees with the right sort of hole. In parts of the east, between a third and four fifths of nests are in trees. The birds are not choosing one over the other. They are using what is there, and the same owl will happily swap between a tree and a barn.

There is more on where and how they sleep in Barn Owl Roosting on the website.

Old sites and returning owls

Some Barn Owl sites are ancient. There are buildings and hollow trees where owls have nested for as long as anyone can remember. Even when a site goes empty for years, it is often reoccupied later, and by different birds. One long running monitoring scheme found that over a third of its sites were empty for a while and then came back into use, on average after about three years. The lesson is a hopeful one. A traditional site is worth looking after even if it looks abandoned.

The perfect patch of grass

What makes a place good for Barn Owls? In two words, rough grass. More precisely, the ideal habitat is a semi permanent stretch of thick, tussocky grass, never mown short and never heavily grazed, with a deep mat of dead grass at its base, at least seven centimetres thick. Field voles love it. It gives them cover from above, plenty to eat and a network of runs beneath the surface.

The numbers tell the story. In a well known Scottish study, live traps in short grazed pasture caught no voles at all. Hay meadows caught very few. Rough grazing did somewhat better. But traps set in strips of rough grass two to four metres wide caught many more voles, and traps in strips four to six metres wide caught more than double that again. In a typical farmed landscape there may be as few as fifteen voles in a hectare. In good rough grassland the number can be in the hundreds.

A good range has other things as well. Bushy hedges, isolated trees and small areas of scrub support a wider range of small mammals, which helps when voles are scarce. Fence posts about two metres high give the owls somewhere to perch. Small, isolated patches of rough grass are surprisingly useful, and owls seem quite happy to fly across less suitable ground to reach them. They do not need everything to be joined up.

What they avoid

Barn Owls generally avoid dense woodland, high ground, busy roads and large towns. In Britain they are widespread but patchy. They are commonest in lowland farmland, especially in eastern England, and more scattered elsewhere, and they are missing from the more remote islands, such as the Outer Hebrides and the Northern Isles. Scotland is home to the most northerly Barn Owls in the world.

Boom and bust

The last part of the habitat story is the vole cycle. In many places, field vole numbers rise and fall over a period of about three or four years. When voles are everywhere, Barn Owls lay more eggs, raise bigger broods and survive better, and numbers climb. When voles crash, some pairs do not breed at all, and the population can fall by half or more. The swings are biggest in the north, where the cycle is strongest, and much gentler in the south. This is a big reason why Barn Owl numbers are so hard to pin down.