Tracking Tawny Owls

Tawny Owls (Strix aluco) are starting to become very vocal again at this time of year.  Nesting earlier than a lot of other birds, the youngsters are at this time of year are becoming independent and are dispersing away from their nesting areas.  The need to find areas to establish their own territories so they will do this by calling, if a suitable area is unoccupied and there is no response they will take up residence and then in mid winter begin calling again to attract a mate. If there is a resident bird already there they will aggressively call back and try to drive the new bird out. 

Picture courtesy of the World Owl Trust (www.owls.org)

Despite being very audible they are usually difficult to spot being almost completely nocturnal and usually frequenting mature deciduous woodland.  You may occasionally catch a glimpse of them silhouetted against the sky as they move from tree to tree or sometimes you may spot them in your car headlights as they drop down on an unsuspecting mouse or vole crossing a country road at night.

Despite this they will leave clear clues around to their presence.  Within their territories they will have several favourite roosting spots that they use but these may be changed on a frequent basis. Normally these will be tucked away against the trunk of a tree, screened behind dense foliage in additional they will also have their favourite hunting perches. Tawny Owls are predominantly “still hunters”, simply perching in one of several hunting perches they wait until they hear their prey moving on the forest floor and then drop down on to it.  At both of these locations they may be signs left behind.  The most obvious sign from a distance will be something that is affectionately known as white wash. Owls and diurnal birds of prey forcefully expel their thick white liquid faeces often leaving distinct white streaks beneath the roost or perch or down it however from this alone it won’t normally be possible to identify exactly what species of owl or bird of prey it is. To do this you will need some additional clues.

Fortunately these can be easy to find. Unlike most birds, owls have no crops and any food the eat passes straight into their stomachs. The stomach acid of owls is relatively weak and so only the softer parts of their prey are digested leaving fur, feathers, bones, insect carapaces etc. virtually untouched. The exit from the stomach into the intestine is quite small and so only the liquid, digested parts are allowed to pass through all the undigested bits are compacted into a pellet which is the regurgitated and eject through the owls mouth. Generally a Tawny Owl will produce two pellets, a large one just before it leaves the roost to go hunting and a second smaller pellet during the night before the second period of hunting activity prior to dawn. Fortunately for us in the UK the pellets of our native species can be distinguished by their shape and size.  Tawny Owl pellets are often pale grey in colour, quite crumbly and about 20-50 mm long compared. If in the open they quickly break up and disintegrate in the rain. The similar sized Barn Owl produces larger, darker, more compact pellets and will be rarely found in woodland.

Because Tawny Owls have quite weak beaks the prey is often swallowed whole, which means that small mammal bones are normally completely intact, including the skull and jawbone which makes it possible to identify exactly what they have been eating. They have an incredibly varied diet which includes mammals up to the size of young rabbits, roosting birds up to starling size, goldfish from ponds, frogs, as well and insects and earthworms.  This means the pellets can be quite variable depending on the diet.  To help identify owl pellets and also their contents the FSC Guide to British Owls and Owl Pellets is very good.

The second clue to be found at roost sites are their moulted feathers. Tawny Owls moult in the summer and will only moult a few of their flight feathers each year so that they are always able to fly efficiently and get food. Although Tawny Owls can be found in two colour phases grey and rufous. In the UK the rufous seems to predominate.  The feathers, particularly the wing and tail feathers will be plain rufous brown barred with dark and pale bands.

Finally is you are very fortunate you may stumble across the track from a Tawny Owl.  Most of their food is terrestrial, which means that when they hunt they generally land on the ground, given the right substrate such as snow, sand or soft mud the keen tracker may be able to detect the distinctive foot print of the Tawny Owl.  Owls have a reversible outer toe, designed so that they can grab and kill their prey by having two toes at the front and two behind, literally squeezing it lifeless like a vice.  The resulting track  is a clear “K” shape.

Right footprint

Whilst tracking on a recent teenager course in our Oxford woods we were lucky enough to stumble across the clear track where a Tawny Owl had landed in a muddy section on a track, leaving a series of prints. The right foot print is particularly clear. The size and location as well as the slightly stubby toes identify it as Tawny Owl as opposed to other species.

For more information on bird sign we recommend the Tracks and Signs of the Birds of Britain and Europe by Roy Brown, John Ferguson, Michael Lawrence and David Lees.