Fifteen Eighty Four

Why were these 17 species such successful colonisers in contrast to most other birds?

Most cosmopolitan birds exploit water environments and because there is water everywhere, with continents surrounded by oceans, this is not surprising! There are just four cosmopolitan species that are not associated with water: pigeons, house sparrows, peregrine falcons and barn owls! Leaving aside pigeons and sparrows, which are globally distributed because humans introduced them everywhere on Earth, we are left with only the peregrine falcon and the barn owl – two species out of 10, 000. This is exceptional!

Why is the barn owl so cosmopolitan?

People usually think that this is because they live close to humans by breeding in our buildings. Since humans have migrated across the Earth, you could assume the barn owl may have just followed us. Wrong! Agricultural practices, which is when we believe humans became settled, began only 10, 000 years ago, long after the barn owl had colonised the planet. Therefore, we are left to find other reasons to explain why this bird is such a good explorer, and was able to settle down once it colonised a new place. A good explorer? This is paradoxical because this owl is not migratory, it only very rarely crosses bodies of water and it is not known for flying exceptionally long distances. To conquer the world, it is therefore not required to be the best flying machine but instead to be able to exploit the newly discovered environments. Even if it takes millions of years to reach every place on Earth, the key aspect is to be sufficiently adaptable to find food and live in new conditions.

What makes the barn owl so amazingly capable of surviving anywhere?

Many biological particularities may have helped the barn owl to conquer the world:

1. Plumage: there are no two identical barn owls. Differently coloured owls exploit the environment in a different way. Because of this diversity in colouration, habitats that may not be suitable for white barn owls may be suitable for reddish coloured barn owls. Animals showing such a huge diversity in colouration are typically better placed to exploit a larger diversity of ecological conditions than monomorphic animals.
2. White as a ghost. The barn owl is the only white nocturnal predator (OK the snowy owl is white but this is to be cryptic in snowy environments) which seems counter-intuitive. Why be white at night and hence more easily detected by rodents? In fact, moonlight reflects on the white plumage which scares rodents to the point that they stay immobile for so long that the owls have enough time to capture them. To look like a ghost to scare their prey, this is the trick.
3. Generalist diet. Barn owls eat mainly rodents but also many other small animals such as birds, reptiles, frogs and invertebrates. This means the owl can go anywhere and will always find something to eat!
4. Killing machine. The barn owl has evolved many adaptations in order to fly silently and capture their prey by surprise.
5. Baby boom. The barn owl is like a passerine, producing large families and raising more than one brood per year! The species can therefore spread very quickly and fill the ecological niches before other species.

Understanding why the barn owl is cosmopolitan requires knowledge about every aspects of its biology. This is why our research group has been dedicated to studying the barn owl for 25 years and counting! This is also why I wrote this new book (Barn Owls: Evolution and Ecology) that compiles the knowledge accumulated worldwide. To this end, I read 3,696 papers written just on the barn owl and relatives (masked owls, sooty owls and grass owls). Barn Owls reports the facts about its evolutionary ecology aspects with an accessible writing style and is illustrated by dozens of wonderful paintings and drawings by accomplished artist, Laurent Willenegger. Even if I am an academic, I was initially an enthusiastic amateur ornithologist. This is why my goal with this book is to present the natural history of the barn owl to a wide audience from academics to the general public.

The study of the barn owl is more than just accumulating scientific data. We are also involved in Education and Environmental Peace building.

Illustrations: Laurent Willenegger

Barn Owls: Evolution and Ecology

Alexandre Roulin