Tawny Owls, Nest Boxes (and Grey Squirrels) …. a year in the life.
It was five years ago that we put up the first nest box in Woodcock Wood designed to attract Tawny Owls. Since then, we have watched, photographed and researched the nesting behaviour of these lovely birds, and are beginning to understand the factors that determine whether they will adopt a nest box and stay with that site over the years.
Noctural In Habit
Unlike the Barn Owl and the Short-eared Owl, which are open country hunters, and often seen during daylight hours, the Tawny is a woodland bird that hunts mainly at night. They hunt from favourite perches, sit and watch, listen and pounce. They get to know the physical features and boundaries of their territories intimately. Their excellent spatial memory and acute hearing enable them to navigate swiftly and safely even on the darkest nights.
Highly Territorial
They hold territories of 50 acres or more, which they defend against other Tawny Owls. Even their own young are driven from the territory in the autumn when they are old enough to have developed adequate hunting skills of their own.
Woodland and Parks
Although they are primarily a woodland bird, they are also well adapted to life in urban parks and wooded gardens. Although rarely seen because of their very nocturnal habits and cryptic plumage, they are the most common of the UK’s owl species. During the day they will perch high in the tree, close to its trunk, and rely on their mottled brown plumage to remain hidden from view.
Provided there is not undue disturbance and change, Tawny Owl territories are maintained over many years. When an adult dies it will be replaced by a young bird looking for a territory.
A Basic Nest is Sufficient
The same nest site is used year after year, provided they aren’t disturbed. Their ideal site is a hole or concealed hollow in an old tree, but in the absence of these, they will nest high up in the crook of a tree or even in old corvid nests. But of course, the more exposed the site, the more vulnerable the young are to attack by crows.
They will also take readily to nest boxes. And as they don’t build nests as such, a few leaves and twigs in the box is adequate nesting material.
Owlet in its nest, high in the crook of a conifer
Generalist Feeders, Except When Nesting
Over the course of the year, Tawnies catch a wide range of prey, from large insects and earth worms, to birds and rats. They have even been recorded as taking large goldfish from garden ponds. But during the time they are feeding their young, their primary diet are voles and mice, which are the perfect size for the young to eat. The owls’ breeding success is closely linked to the abundance of these small rodents in particular years.
Breeding Record 2021 / 22
Although Tawny Owls will vigorously defend their eggs and young, they will readily desert the site if disturbed in the early stage of nest site selection. Therefore I set up the cameras in October, and left them unmonitored until April.
By listening to the owls over that period we were certain they were nesting in one of the boxes. By April I was confident the adults wouldn’t abandon the nest, and checked the box on 21st. There were two young owlets on the floor of the box. On the 15th May, the two owlets left the box.
Using our observations and camera record, we have developed the following story:
During late summer and early autumn the pair tend to go their separate ways within their territory, using a number of favourite hunting and roosting spots. This will also be the noisy season for the owls, as it is the time that this years’ fledging tawnies are leaving the area where they were reared and trying to find a territory of their own. Our Tawnies will be keeping a wary eye open for intruders and driving them out with much hooting and calling.
In late October, our pair come together again. The pair bond is re-established around November, and courtship displays take place around the chosen nest site – see video 2 below. We recorded this a couple of years ago, when the pair were checking out one of the boxes. It gives some idea of the intimacy of their relationship at this time of the year.
During autumn the cameras show a lot of activity close to the box, and not just from the owls. A number of birds take an interest … from the general curiosity of the Great Tits and Blue Tits investigating any holes and cavities, through to the challenge of the Jays, and the genuine interest of the Stock Doves (the pair nested in this box late in the season in 2021).
Squirrels
The main competitors though are Grey Squirrels. There is a very uneasy relationship between the two species. As video 1 shows, the owls can be extremely swift and aggressive in the confrontation, and squirrels are certainly wary of them. But quite often what we witness is a standoff position.
It seems from our observations though, that once the owls have selected their site they are well able to defend it. But the problems arise when squirrels get to the box first, and start to fill it with leaves and twigs.
They can do this at tremendous speed. We have seen them fill the box from empty to full over the course of a day. This renders the box unusable for the owls. The owls would make no attempt to empty it. The squirrels then have their drey complete, and the owls would need to go else where.
During the early autumn we empty the box of twigs to try to prevent this outcome. The provision of the box is an artificial situation for owls and squirrels, and we regard the emptying as a necessary part of that intervention.
Incubation and the rearing of young
Working backwards from the owlet’s fledging date of the 15th May, the eggs would have been laid during the first week of March.
The female laid two eggs. She undertakes all the incubation and relies on the male to bring her food. The eggs hatched around the 18th April. The owlets were hidden from view for the next 3 to 4 weeks, but the camera showed clearly that the female was feeding young.
On the 12th May an owlet first appears, followed shortly after by its sibling.
Over the next 3 days the two make regular appearances, singly or together, exploring a little along the branch, stretching their wings, and most importantly looking … adapting their eyes. The video illustrates this well.
On the 15th I checked the box, and both owlets were inside. On the same day they both left the box, either climbing into the tree canopy, or flying a short distance and then climbing.
… and then?
Well, and then. it is tough! Research suggests that the owlets are at their most vulnerable during the first 10 days after leaving the nest. Foxes and corvids are the most frequent predators. During this time the owlets tend to spend time near the ground. As they grow stronger they are more able reach higher into the tree canopy, where they are safer from predation.
But hunger is also a factor, and in good years for voles, the young owls are more likely to survive.
Research also suggests that the stronger the owlet when it leaves the nest the better its chances of survival. Nesting in the type of box we have provided means the owlet has to be strong to clamber up and out onto the ledge. The video shows this well.
Owlets nesting in open crooks of tree trunks are more vulnerable to just toppling out of the nest before they are really ready to leave.
Sadly, neither this little fellow nor its sibling (photographed still in the nest, above) survived more than a couple a days. From its appearance and development of its feathers, it seems younger and weaker than this year’s pair, when they left their nest box.
If the two survive their first two weeks, then they will be fed by the parents until they have developed independent hunting skills. In early autumn they will be driven out of the territory and will have to find a suitable patch, not yet occupied by a Tawny Owl pair, or a territory occupied by a single owl of the opposite sex – not an easy task for them. Unlike fledgling Buzzards, they don’t travel far, two or three miles at the most. Many won’t meet this challenge.
It is a sad fact that about 80% of this year’s brood won’t make it to through their first year of life. It is tough for these endearing birds.
Video 1: A 4 minute video illustrating some of the points in the blog:
Video 2: A short video of Tawny Owls selecting nest site / courtship display:
Also, see our earlier blog that describes the boxes and position of the boxes in Woodcock Wood: https://woodcockwood.com/tawny-owls-and-nest-boxes/
Chris and Chris Saunders May 2022
[…] See also for a discussion and video of the Tawny Owls breeding success during 2022: https://woodcockwood.com/tawny-owls-nest-boxes-and-grey-squirrels-a-year-in-the-life […]