Owls, Humans, Rodents, and Food Loss

Owl Hole under the eaves on a barn in Wiltshire, England

See that hole high up under the eaves of the barn. Check the little landing platform under the hole. That’s a hole for a barn owl (Tyto alba).  (Ignore what looks like an L-shaped extension to the left. Those are the outhouses of the farmhouse across the yard).

And perhaps, while you are at it, admire this lovely two-story nineteenth-century barn built of Jurassic limestone, rubble for the walls, dressed stone for the corners, roofed with Welsh slate. Dairy cattle spent the winter on the lower level, the loft above that right up to the rafters held straw for bedding and hay for feed. Originally there was an open passage through the middle of the barn, now covered with black corrugated iron. In the fall the year’s wheat, oats and barley would have been threshed there.

Grass seed, weed seeds, and grains made a perfect feast for mice and voles (rats too, but rats are too big for owls).  European farmers, then, from at least the seventeenth century and probably long before, constructed owl holes to encourage owls to nest in the safety of their barns.

In a year a nesting pair of owls and their young could do away with 1000 of those little mice and voles that gobbled away at the farm stores.

Barn owl with its prey. CC. Norfolk Wildlife Trust. Elizabeth Dack Strumpshaw. 2013

It’s a lovely example of the intersection of the wild and the cultivated, the natural and the artificial, wildlife and humans.  Going in to the farm yard at night and seeing a barn owl swooping by almost silently in the dusk was a treasured experience.

By the late twentieth century, though, the numbers of barn owls in England (and in many other places) had plummeted. Precise figures are impossible to come by but estimates suggest that they fell by 70% between 1932 and 1985. In England, the Barn Owl Trust started a campaign of monitoring nests, erecting nesting boxes, and weighing and measuring the young.

All kinds of causes have been suggested for the decline.  Perhaps it was the pesticides used to decimate the rodent population. Perhaps it was the huge increase of fast moving vehicles on the roads.  Perhaps it was the change in farming methods. With the tractor, horses disappeared from farms and so did the hay and grain that was their food. With the combine harvester, threshing was no longer done on the threshing floor.  With the building of corn dryers (elevators in the US), grain was corralled by metal that rodents could not chew through. With the closing of dairies, hay was no longer stored in the lofts.

Probably all three causes played a part.  But it’s the last that interests me. And, be warned, the following are ruminations, not my main area of expertise.

There are now many, many studies of post-harvest waste of grain with traditional farming methods.  Moisture, mold, insects and rodents all take their toll, destroying as much as a third to a half of the grain harvested.  Technically this should be called loss, not waste, because the grain is not thrown away but lost to damage. Often, though, loss and waste are rolled in together particularly when authors want to bring about change.

In England (and elsewhere), post-harvest grain loss has fallen to a negligible level–a good thing surely.

But the fall in post-harvest grain loss has been accompanied by the decimation of the barn owl population–not such a happy result for a bird that has lived in symbiosis with farmers ever since there have been farmers.

Life is complicated.

One last thing. The recommended feed for adopted baby barn owls is dead day-old cockerels.  They are dead because they won’t grow up to grow eggs. Currently there are moves to try change breeding techniques so that only hen chicks are born or to argue that eggs should not be eaten.  More trouble for the barn owl?

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