Chapter 13 of 23

Survival, Dangers and Numbers

Why life is short for most Barn Owls, and how many there are

About 5 minute read

A short life for most

It may surprise you to learn that most wild Barn Owls do not live very long at all. Of all the young owls that leave the nest, only around one in four survives its first year, and some studies suggest the figure is a bit higher, at up to about a third. Adults do better, with roughly two in three surviving each year. A bird that gets through its first year can expect to live to around four years old, and a bird that reaches five is considered an old one.

Some do far better. The oldest wild Barn Owl found through British ringing records was a little over fifteen years old. Owls in captivity, safe from hunger, traffic and bad weather, often live to twenty or twenty five, and one bird at an owl centre in Gloucestershire reached the astonishing age of 34, confirmed by the paperwork attached to its leg ring. The gap between the wild and the captive birds tells you how dangerous the outdoor life really is.

Experience counts, too. In one long study in Scotland, a bird's chance of surviving another year improved as it grew older, from around a quarter in its first year to nearly two thirds by its third. An owl that has learned to hunt from fence posts in the cold and to roost between straw bales is a better survivor than a youngster that has only ever hunted on the wing, and slept out in the open.

When do owls die?

The deaths come in two waves. The first and biggest is in autumn, when the young of the year are dispersing and are most likely to starve, get soaked, be killed by a fox or a buzzard, or be hit by a car. The second comes in late winter, in January and February, when both adults and first year birds run short of food and the weather is at its worst. Spring and summer are safer times, at least for those who have already settled.

The hazards

The list of things that can kill a Barn Owl is long. Here are the main ones.

• Starvation. A Barn Owl carries very little fat and cannot go long without food. A run of wet or snowy weather that stops it hunting can be deadly, and so can a crash in vole numbers.
• Cold and wet. Soft feathers soak up water, and a wet owl cannot fly or keep warm.
• Roads. Grass verges are full of voles, and owls hunt along them and fly low across the road. Road deaths are one of the biggest known causes, particularly for young birds dispersing in autumn and for adults in late winter, when they roam furthest. Major roads seem to take birds that would otherwise have survived.
• Poison. Rat and mouse poisons, particularly the powerful second generation types, can pass along the food chain when an owl eats a poisoned rodent. Tests on dead owls have found traces in a large share of them. The full effect on their health and their numbers is still not known.
• Water troughs. Barn Owls trying to bathe or drink sometimes fall into deep, steep sided containers such as cattle troughs and drown, because they cannot climb out with wet wings.
• Wires and fences. Owls flying low sometimes hit overhead cables and other obstacles.
• Predators. Foxes take owls that end up on the ground, and buzzards occasionally take young ones by day. Adults have very few enemies.
• Falls from the nest. Owlets that tumble out of a nest with a low entrance often cannot get back in, and are ignored by their parents.
• Loss of homes and hunting grounds. Old barns are converted or collapse, hollow trees are felled, and rough grassland is ploughed, mown or overgrazed.

None of these hazards is new, but taken together they mean that a pair of Barn Owls is always living a little on the edge.

The people who study them

A lot of what we know comes from volunteers and researchers who have spent years watching, ringing and tracking owls. They fit tiny radio tags, weigh and measure nestlings and follow them for months. They look at nest cameras. One of their most important discoveries is that the survival of young owls after they leave the nest matters more to the total population than any other stage of life. Raising the number of young that survive their first winter would do more for Barn Owls than laying more eggs or fledging more chicks.

How many are there?

Nobody knows exactly, and it is worth being honest about that. Barn Owls are hard to count. They are mostly active at night, they nest in hidden places, and their numbers can double or halve in just a few years as voles come and go.

The best picture we have goes something like this. In 1932, a survey estimated about 12,000 pairs in England and Wales, and it was already clear that numbers had fallen over the previous decades. They declined further in the middle of the twentieth century, hit by pesticides, the loss of hunting grounds and the harsh winters of 1947 and 1963. A big national survey in the mid 1990s, called Project Barn Owl, came up with about 4,000 pairs for the UK, give or take around a third. That was the first reliable count. Since then, no one has managed an equally trustworthy nationwide figure. Sightings and nest records suggest the population grew for a while, and figures of 10,000 pairs or more have been suggested, but the numbers have also swung up and down with the weather and the voles.

What we can say is that the Barn Owl was moved from the Amber list of conservation concern to the Green list in 2015, reflecting the fact that it was doing better than it had been. It is a bird that has improved, and yet it is still one bad winter away from a bad year.