Know-how to Wow an Owl

Tawny Owls ( Strix aluco ) generally do not build a traditional nest structure. They select a ready-made nesting site instead, which they often choose in the autumn. Here are the details of their breeding behaviour.

The Nest : Tawny Owls do not build a nest with materials like sticks and leaves. They typically use a cavity in a mature tree, an old nest of another species (like a crow's), a crevice in a building, or a purpose-built nest box. They claim the site, and the female makes a shallow depression, or ‘scrape’, in the debris already present in the cavity, a process which takes place in the autumn or winter, well before egg-laying.

Egg-laying : Egg-laying in the UK usually takes place in late winter or early spring. The first egg is typically laid around mid-March, though it can be as early as February in mild conditions. They lay a clutch of 2-3 white eggs, with incubation starting immediately with the first egg.

Territoriality : Yes, Tawny Owls are highly territorial and are resident, meaning established pairs remain on their territory all year round. They fiercely defend their territory to secure familiar hunting grounds for themselves and their young. Territorial behaviour peaks in the autumn when young birds are dispersing and trying to establish territories of their own. They are known to be quite aggressive in defending their space, even towards humans approaching a nest.
Bird photographer Eric Hosking lost an eye to a tawny owl, hence the title of his autobiography; ’An Eye For a Bird‘ (1973)

What you've found is an important clue, but it points to a potential competitor rather than the Tawny Owl itself. Here is a breakdown of what the twigs and leaves most likely indicate:

1. The twigs and leaves are unlikely to have been left by a Tawny Owl as they do not build a nest. They are cavity nesters, meaning they use natural holes in trees or man-made nest boxes. They do not bring in their own nesting materials. If you have provided a substrate (like wood shavings or chips) in the box, the female owl will simply make a shallow ‘scrape’ in that material to lay her eggs.
   A collection of twigs and leaves is the classic sign of a Grey Squirrel or a Jackdaw. Both of these species will aggressively colonise an owl box, often filling it with material very quickly to create a drey (squirrel nest) or a typical bird's nest.
2. Is it Still an Owl Territory? Even if the material was put there by a competitor, it doesn't mean the Tawny Owls haven't noticed the box or aren't in the area.
   The most reliable sign of a Tawny Owl territory is their calls. Since it is now October and autumn, this is when their calling is at its peak. This is because young birds are dispersing to find territories, and established pairs are defending their boundaries in preparation for the upcoming breeding season.
   Listen for the classic male's hoot: “hooo hu huhuhuhoo”. Listen for the female's sharp contact call: “kee-wick”. The well-known “twit twoo” sound is actually a duet between a male and a female.
3. Roosting Behaviour . If a pair of Tawny Owls are in the area and have claimed a territory, their roosting behaviour is as follows:
   Roosting Location : Tawny Owls roost during the day, usually in the dense cover of a tree, often close to the trunk or in another natural cavity within their territory.
   Proximity to Nest Site : If they have been checking out or are intending to use your nest box, they will generally roost somewhere very close by - in the same tree or an adjacent one as they need to be vigilant about defending their chosen site from rivals such as the one that left the twigs!
   Cleaning the Box : If your intention is to attract a Tawny Owl, it is advisable carefully to clear out the twigs and leaves left by the competitor now, in the early autumn, to make the box available for the owls to claim for the winter/spring nesting season. Make sure to wear gloves and check for any occupants (like a sleeping squirrel) before cleaning it out.

That is exactly the right action to take after clearing out the competitors’ material! Because Tawny Owls do not build a nest, they need a soft substrate in the box to create a ‘scrape’ to hold their eggs safely and prevent them from rolling around or getting chilled on the bare wood. Here is the best advice on what to add.

• Recommended Best choice for Substrate : Wood shavings, wood chips, or shredded bark. These provide insulation, drainage, and a soft base for the owl's eggs.
• Quantity : Aim for a layer of about 5 to 10 cm (2 to 4 inches) deep across the floor of the box.

What to avoid .

• Fine sawdust : This can be a problem as it can stick to food the parent is tearing up and be ingested by the chicks, which can cause health issues.
• Soil or sand : These are generally less suitable as they can become cold, wet, or heavy, and they do not provide the same cushioning and drainage as wood products.*
  * Hay is also not recommended as a possible source of parasites or fungal spores.

Timing As Tawny Owls choose their territory and nest site in the autumn and winter, right now is the perfect time to make the box ready for them. By adding the wood substrate now, it gives any potential resident female the chance to settle in, claim the box, and make her ‘scrape’ready well in advance of the early breeding season (which starts in late winter/early spring). So, once you have safely removed the twigs and leaves, a generous layer of coarse wood shavings is the ideal way to make the box attractive and functional for a pair of Tawny Owls.