Barn owl boxes clearly help these much-loved birds build their nests and raise their young — but it’s important to resist over-monitoring
I’ve been building barn owl boxes for the past few years. We have some excellent habitats for barn owls across the open moors and rough field margins, but our main problem is suitable nesting sites.
There is no shortage of trees in this part of Galloway but the huge majority is commercial softwood; trees like Sitka spruce and lodgepole pine. These vast plantations have little value for breeding barn owls and, while the birds sometimes roost in the deep thickets, they do not have much to offer nesting birds. The dark, swaying trees are much more useful to long-eared owls, which lay their eggs in the abandoned remains of crow nests.
There are a few old ash trees out on the hill and I worked hard to get boxes up where I felt they would do most good. Some of this effort was misguided and one of my boxes has now been up for eight years without a single sign of occupancy. I was on more reliable ground hanging boxes in the rafters of old cattle sheds and one seemed to have instant success; a white feather was found on the hard earth floor less than a week after the box was put in.
I resisted the temptation to look too closely at the nest box for fear of disturbing the occupants, so I set up my trail camera nearby to see whether or not the box was “active” or whether I had simply had a single visitor. I returned the following day to find my memory card full of photographs.
Two owls had bustled and shuffled around the platform of the box for several hours and I flicked through the images with delight. Resisting the temptation to over-monitor the box, I withdrew and let the sheds return to peace and quiet. A fortnight later, I heard owls calling from the shed when I was out lamping and was thrilled to think that my box was helping them.
I returned later in the summer to reset my trail camera. I reasoned that chicks would now be emerging and I wanted to get some footage of the youngsters. By this stage I had been granted a licence to check barn owl boxes from Scottish Natural Heritage as part of a long-term barn owl monitoring project in Galloway. Ten days went by and the camera revealed that the only activity at the box was a visit from a single pigeon. From this I assumed that the coast was clear and went in for a closer look. A thick cobweb across the doorway added further proof that nobody was home.
Peering in through the door, I found that the box was carpeted with a deep bed of dead voles. Mounds of corpses lay strewn in a mat almost 3in deep and many of them were mummified, frozen forever in a dry, twisted rictus — little yellow teeth bared like Egyptian mummies.
In the far corner of the box were two small, white, almost spherical eggs. I came away from the box quite confused. Reading through my books on barn owls, I found that barn owls can lay large clutches of eggs and one or two often don’t hatch. It’s possible that these owls reared a large brood of healthy owlets and the two eggs were simply the leftovers, but I couldn’t reconcile the thought of large, mucky, scuffling chicks crowded together in a small space for an extended period without leaving a single mark on the pure white eggs.
It seemed more likely that the nest had been abandoned after only two eggs were laid, but judging from the vast surplus of food that had been gathered and wasted, it was hard to see hunger as a cause. I can’t ignore the possibility that disturbance might have played a part, since this is a functioning agricultural shed that can see lots of activity during the summer months.
To some extent this is unavoidable, but my family remembers barn owls breeding in these sheds when they were in far more active use. I’m confident that the box is in a suitable spot but if disturbance did play a part, we must take extra care next year.
There is also the chance that one, or both, of the adult owls was predated. We have a healthy population of goshawks in the forests around the hill and it is not uncommon to find the remains of dead barn owls strewn around their favourite plucking posts. Whatever the reason,
I am tantalised by this progress and can’t wait to experiment with more boxes.
“It’s possible that the owls reared a healthy brood and the eggs were simply leftovers”
Patrick Laurie is a project manager at the Heather Trust. He has a particular focus on blackgrouse conservation and farms Galloway cattle in south-west Scotland.
A barn owl at a nest box; old cattle sheds make good sites for nesting boxes for these shy birds