Birds not rodents fill owls' beak

Most people would skip rats and mice as a menu item and so it seems do short-eared owls.

The long standing assumption was that owls provide a major service to humans by gobbling up rodents, but a new study shows they prefer munching their way through local birds instead.

A study at a coastal site at Ballymacoda, Co Cork revealed that of 1,030 prey items taken by short-eared owls, birds accounted for more than half of the total number but 83 per cent of the total by weight.

Only 17 per cent of the prey by weight was accounted for by rodents and other mammals.

The short-eared owl (Asio flammeus) is a regular visitor here and while resident it forages for just about anything it can catch, bird or rat, said authors Chris Cullen and Patrick Smiddy, writing in Biology and Environment: Proceedings of the Royal Irish Academy.

Previous studies of the owl were relatively small but this one involved sampling prey items over six winters. The authors then added another year’s study conducted in 2005 to account for more than 1,000 prey items taken by the owls.

Most of the assessment involved studying the contents of owl pellets but also bones and other debris left behind after a meal. Most often on the menu was the dunlin or sandpiper, along with snipe and redshank.

The thrust was also popular, accounting for about 10 per cent of the total weight of prey eaten by the owl. The unfortunate wood mouse was the most popular mammal species, amounting to just over eight per cent of the weight taken.

Other rodents and shrews were also caught and eaten, the authors say in their report.

They speculate that the severe winter of 2010-2011 may have influenced things given more birds and fewer mammals than expected were taken by the owls.

The authors argue that studies of the diet of top predators such as owls can contribute to their conservation.