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Owls: A Guide to Every Species in the World

Found on every continent other than Antartica, the owl is anything but an unexceptional bird. Their piercing gaze, uncanny ability to swivel their heads in the round, and their spooky stealth has long made them the subjects of art, literature, and films. And even those only slightly interested in birdwatching can’t help being thrilled by hearing or seeing an owl in the wild.

But there is a lot more to know about owls than just the basic facts and mythologies about these remarkable predators. The best place to start may well be Owls: A Guide to Every Species in the World (Harper Collins; Nov 2016; U.S. $50). This fascinating owl encyclopedia was written by Marianne Taylor, author of a dozen natural history books, including Beautiful Owls and Owls. Her most recent owl book explores all 225 known species, from the snowy owl in the Arctic tundra to the burrowing owl of the Mexican deserts;  from the enormous eagle owl that preys on young deer and foxes, to the elf owl that eats insects.

Apart from detailed profiles and images of each of the species, Taylor provides a lot of fascinating information about how owls see, hear, fly, hunt, mate, and more. In an email exchange with Voices, she shared some of the secrets of one of the world’s most charismatic birds:

There are some 220 or so species of owls in two families. What are the families and what differentiates one family from the other?

The families are Tytonidae (barn-owls) and Strigidae (true owls). Nearly all owls are in the family Strigidae. Barn-owls make up a small, distinct family of about 20 species. They are all rather similar with relatively long, heart-shaped faces, long legs and small eyes, and their plumage tends to be pale and without strong patterning. The two families are also differentiated on the basis of small but consistent details of internal anatomy, which reveal that their lineages separated at an early point in owl evolution.

We think of owls as being mysterious creatures of the night. But some are diurnal. What makes them so, and what niche have they carved out for themselves in the daylight?

Most of the diurnal owls are birds of open countryside and are also active hunters, flying low and slow and listening/watching for prey, rather than using the more common owl tactic of sitting in a hidden spot and waiting for prey to come close. So these diurnal owls occupy a similar niche to certain day-flying birds of prey, particularly the harriers, and indeed come into competitive conflict with harriers on occasion.

Owls famously can turn their heads, apparently some of them almost full circle. How can they do it and why have they developed such an ability?

Owls have exceptionally flexible necks. The neck is also long (which is not obvious when you look at an owl, but very obvious when you look at an owl skeleton!) The ability to turn the head so freely compensates for owls’ lack of ability to move their eyes easily within the eye sockets. The owl eye-ball is tube-shaped rather than spherical, which allows for a larger retina (the part of the eye that contains light-sensitive receptor cells), and the eye socket has extra bony plates to support this elongated eyeball. However, it means owls cannot easily glance from side to side as we do, so instead they turn their heads.

From your book I learned some fascinating insights about owls’ eyes, which most of us know as bright yellow and piercing. Yet there are some special features that enable them to see in very dim light. Tell us a bit abiut the structure and capabilities of their eyes.

The large retina (as mentioned above) is key – more space for light-detecting cells. So is the make-up of the retina. Vertebrate eyes have two kinds of light-detecting cells – rods, which are highly sensitive to light levels, and cones, which are less sensitive and react to specific wavelengths of light that correspond to a particular colour. Our eyes contain three kinds of cone cells, mixed in with rods. In most birds there are four kinds of cone cells, meaning they have more refined colour vision than we do. However, owl retinas contain nearly all rods, which means they have poor colour vision but can detect even the slightest contrast. This is much more useful after dark. Also, behind the retina is a reflective membrane (tapetum lucidum) which bounces back light. This gives the retinal cells a ‘second chance’ to react to the light.

You say owls have good telescopic vision (like humans), but they can’t see objects at close range; they have other ways to lock on to their prey when they are about to strike. What are those?

Most owls use their extremely accurate hearing to target their prey. At close range the fine whisker-like feathers around the owl’s bill (the filoplumes) provide sensory information – such as whether the prey they have caught is still moving or not.

Yet you say vision is not the strong suit in the owls’ senses? Their real superpower is hearing. Can you describe a little about how their physiology has adapted to be such efficient listeners, and how they can pinpoint their prey in the dark just by what they hear.

Owls have very sensitive hearing, and the distinctive shape of their heads with the facial disk of stiffened feathers helps to channel sound into the ear openings, located on the sides of their heads. The ear openings are assymetrical, so sound coming from directly below or above reaches one ear before the other. This enables them to determine the source of a sound in three-dimensional space with pin-point accuracy, so they can pounce at exactly the right spot with no need to set eyes on the prey that is making the sound. Additionally, the area of their brain devoted to processing input from the sound receptors in their ears is proportionately very large. Their highly sensitive and accurate hearing means owls can hunt in near darkness and can also catch prey moving under a layer of snow – so owls of the far north can often stay on their territories through winter when other birds would be forced to move south and risk being unable to reclaim the territory when they return.

Harry Potter and many other stories and movies portray owls as wise. But you say they are not the smartest birds. Where do they fall in the spectrum of avian intelligence?

Like most predators, owls (especially larger species) are reasonably bright, certainly in the top half of the class, as it were, as they need to find ways to outwit their prey which includes some pretty intelligent mammals. But, by the criteria with which we usually assess intelligence (speed of learning, innovation, problem-solving etc), they are not up to the level of the really clever birds like crows, parrots and gulls. These species are noted for being very adaptable and inventive, as well as highly social and able to learn from one another. Owls are rather more creatures of habit, and much more solitary. However, as falconers can tell us, owls can learn new tricks and tactics quite readily with patient training, and can also build strong affectionate relationships with their owners.

Owls are superb hunting machines, and not just because of their vision and hearing. They are also extremely stealthy and have various ways to search for prey. Tell us a bit about that.

Many owls use a ‘sit and wait’ approach when hunting – they find a well-concealed perch and wait silently for prey to come into range (either they see or hear it). The actual swooping attack is silent (thanks to modified flight feathers which muffle the sound of their wing-beats) so the prey usually knows nothing of the danger until it’s too late. Owls that hunt actively also fly silently, which means they can hear prey easily, and their long legs allow them to strike at it even through long grass.

I remember as a child a tracker looking for and showing us owl pellets. Where would you look for those and what do they tell about the owls in the neighborhood?

Owl pellets can be found near nests and regular roosting spots. Analysing the contents of pellets reveals the owl’s diet and can give an insight into which prey species are present in the area. Some small mammals’ distributions are only known in detail because of studies on owl pellets. Studying owl diet is much easier than with most other animals, because they swallow their prey whole so pellets contain intact and easily identified bones and other indigestible prey parts.

What are the biggest threats to owls, both in nature (what preys/troubles them) and from the human world? What can we do to help them survive?

Habitat loss is the biggest threat, mainly due to human activities like clearing forest (specifically removing the large, old and partly decaying trees that are most likely have cavities that can harbour nesting owls). Also, some farming practices can be harmful. Many owls hunt on open ground adjacent to the woodland where they nest, so loss of hedges and wild field margins, and excessive pesticide use, all reduce prey for owls. Providing nestboxes mitigates loss of good nesting trees (particularly helpful for the larger species of owls). Buying organic produce supports wildlife-friendly farming practices.

Are there any interesting tidbits to learn about the mating habits, gender roles and territorial behavior of owls?

Unpaired male owls hold territory and “sing” to attract a mate. If a male’s territory is productive enough and holds good potential nest sites, an unpaired female will join him. A bonded pair perform “duets” to help affirm their bond, and to discourage rivals of both sexes.

In almost all species of owls the females are distinctly larger than males. Their role in breeding is to stay at the nest and guard eggs and young from predators – a riskier task than the male’s, which is to catch prey and bring it to the nest, for the female and the chicks.

Once the chicks are larger and hungrier the male can no longer provide enough food on his own, so the female begins to hunt for the family as well. By this stage the chicks are stronger and better able to defend themselves, so it is less risky to leave them unattended.

What tips do you have for people who want to look for owls? They can be extremely difficult to spot, especially in the day.

The day-flying owls (like Short-eared) are easiest to see, and are most likely to be out hunting from mid-afternoon, on fine days with a light breeze, especially in summer when they probably have a nest full of hungry chicks to feed. They use the wind for uplift so are more likely to fly closer if you position yourself with the breeze behind you. Finding territories of nocturnal owls is possible if you listen for them at night, and then search areas where you’ve heard them, looking for holes in trees that could be nest-sites, and for pellets on the ground that would reveal a roosting spot. Owls are very loyal to their nest-sites and favourite roost sites, so if you find one such site you may be able to observe the owls there for many years. Be mindful when searching, though, that many owls are strictly protected from any kind of disturbance and some can be fiercely aggressive to intruders near their nest, and don’t approach too closely.

Marianne Taylor is a freelance writer, illustrator, photographer, and editor. Her interest in natural history began at an extremely early age, as she became passionately interested in first butterflies and then birds. The daughter of two librarians, one of whom later became a secondhand bookseller, Marianne was as bookish as she was bird-obsessed. She worked for seven years in natural history publishing, first for bird book publisher Christopher Helm, and later for Birdwatch magazine. Her particular interest in owls and other birds of prey was fueled by a brief but unforgettable adventure in 2005, when she joined bird ringers studying Ural, Tengmalm’s, and Eagle owls in the forests of Sweden. She began a new career as a writer in 2007, and since then has written more than a dozen books for adults and children on a range of natural history subjects. Her previous work includes RSPB British Birds of PreyBeautiful Owls, and Owls.