Some Thoughts on Owl Nesting Boxes, and Rodenticides.


392 Barn owl iat roost in quarry JF 5770 PP DFine (2)

Image of Natural Cliff nest in quarry, owl visible in darkness


BAO Box PPoi0379_RJ II (2)                                                                                                                                                                                            Newly made nest box
General talk about Owl Nesting Boxes
Here in Southern Africa, like in other parts of the world, the Barn Owl [Tyto alba] and its other subspecies, are the number ONE rodent catchers. Their impact as biological rodent control is huge, especially in the grain and grape producing areas.
Other owl species , like the Marsh owl[ Asio capensis ] , African Grass-owl[ Tyto capensis] and Spotted Eagle-owl[Bubo africanus] also play a role in rodent control, but to a much lesser extent. These owls are more specialized in the prey they take, whereas the Barn owl, which has a wide spectrum of prey.
The most a frequent asked questions I get at my slide shows or talks that I do on owls, have been in the past, “what camera or lens are you using”, or “aren’t the owls scared off by the flash “. Nowadays people say “ I have owls near my house and would like to put up an owl box ,where would be a suitable place ” or “ ’ we have a rodent problem, but don’t want to use poisons” .
The Good News is……..
People are more aware that owls provide a free, environmentally safe option to rodent control. Especially wheat and pig farmers, which have a surplus food available, who has realised that owls have a positive impact on their property and livestock.(see articles from the Western Cape) A breeding pair of owls which has to feed their young is the best solution .
City dwellers on the other hand enjoy nature by hearing owls call at night or to see them sitting at night on their favourite hunting perch.
Although here seems to be a constant search for suitable nesting sites for owls, nesting boxes are not mysterious contraptions!
As you can see from the illustrations, the boxes can be made of the materials that are cheap to come by, especially If you have timber or wood lying about your property, use your imagination and some improvisation. Don’t waste good timber to meet the exact millimetre sizes.
The size and way of the box opening face are the two important factors when constructing an owl box. The opening should not be too large and not face an area with high activity. Thus the owls will have a darker area to “hide” and would not fly off every time someone passes the entrance. A large opening will also allow other predators like crows to harm owlets. Facing away from direct sunshine is better.



Western Barn Owl chicks still in Nesting box





Even the size of the box is not so critical, but keeps in mind that owls regularly raise six chicks, and the box must accommodate them, and perhaps the female/mother too!   (See photo chicks inside box)

Owl chicks still in the nest box Young barn Owl nestlings in the box
The measurements see slide, is a standard that I try to keep to, but I have found a lot of natural occurring nest spaces used by owls, much smaller and more cramped, than a good owl box. (See Cliff nest in opening paragraph)
Try putting the box in a protected area, in a barn, under a roof overhang, or under covering of a tree, at a height of about 3 meters high, to keep it out of “h/arms way”. Some people have success in putting it up on an isolated pole (photo Stellenbosch), but such a box can get rather hot and cramped. Some roofs material e.g.. Corrugated iron, which leaves ventilation through on hot summer days, is ideal. This is necessary even when the owls are not breeding as the parents use the nesting box to roost in during the day.


Dimensons of a Standard Western Barn Owl Nesting Box


Tri-Angular Box , new research


Diagram of Artificial Nesting box
Floor 500 x 400 mm
Height 400 mm Opening 120x 150 high Barn Owl nest box in Vineyards in Stellenbosch suburbs

Tri-angular owl nesting box
Another option is tri-angular boxes, as seen in the illustration at Spier Rehabilitation Centre. They are much easier to carry and put up, has an inspection door to clean annually and ring the chicks. There are also large ventilation holes near the top, which limits the nesting of bees. So far I have not had records of the preference of the owls to the new concept.
Owl boxes do not leave a negative impact on the environment. As soon as not needed in the area, it can be moved or eliminated.
By just utilizing the owls present, some farmers have cut down on their use of pesticides to as low as 20% of their normal use.
As Quartus Laubscher of Cloeteskraal, Hopefield district mentions in an article in magazine Country Life of April 2011 ,” the river of poison , flowing into our streams , would be a slow trickle” on his farm and also neighbouring farms owned by likeminded farmers,( See photo Jan Kotze , inspecting his nesting boxes Baartjieskraal, Western Cape , near Laaiplek/Veltdrif .)

Farmer checking owl nesting box next to lands



Farmer checking his Barn Owl Box next to his fields



How do we start the box to be active? Or advertise to the owls
We can just supply the box, and if the owls are around, and they are in need of a roosting place or nesting box they will find it. Sometimes it takes a long time, which means, either they had a good place otherwise, or that a new pair moved into the area, or some of the previous brood is still around. Even if other birds, like speckled pigeons find it first, the owls will evict them and clean out the twigs and nesting material, take over the box without much ado. (Zeta WRT box)
The other tenants that are not so easy to evict are HONEY BEES and WASPS, and an eye should be keeps on the box regularly, try to evict them as soon as possible, because when they are in, they are IN!


BAO Box PPoi0358_RJ II (2)





Owl Box taken over by Bees IMG_8125 Selection of Owl and Bat Boxes

Nesting box taken over by bees               Inspecting owl box attached to house

When bees are seen flying around the entrance and inspecting the inside , a well-placed mosquito coil is enough to get rid of them. Be warned once they have built their combs and fixed the wax to the walls or roof of the box, you might as well write off the box. The bees will return time after time, notwithstanding the washing with detergents, like Jeyes Fluid, and spraying with Doom etc., or with Bye-Bee-Bye .
Using old wood , saturated with old oil, as building material ,seem to keep the bees away from building nests. It may even deter wasps too. The wood should not be so “wet” with oil as to soil the feathers of the owls.

                                                                                                                    Display of owl boxes for Barn and Spotted Eagle-owls.(Spier Rehab Centre)

Another question is how far apart should these boxes be put up , or specifically , how NEAR will a breeding pair tolerate another pair to their territory. My past experience was approximately 80 meters apart. The one nest was in the ceiling of a barn and the other on the floor of an open silo. I the one nest in the silo probably belonged to off-spring from the other older nest.
During breeding the birds will be more tolerant of having off-spring around , but in the off-season they will be forcefully evicted from the breeding territory. In the Western Cape , owl boxes were put up at very close distances of each other , but it may be that not all were nesting boxes , some might be just have been roosts where male and females were in separate boxes.
Beware of owl Nest Box manufacturers that claim they have boxes that suit every species of owl. Some owls are so specialized in their manner of nesting that it is impossible to build boxes for the “Nesting Specialists”.
The first few species that come to mind is the African Grass-owl [Tyto capensis ] and the Marsh owl [ Asio capensis]. They breed on the ground in grass and very choosy about the area.
Cape Eagle-owl[Bubo capensis ] is a ground or cliff nesting owl, and very specific in its preferred nesting area.
Some years ago Charles Chinning had a project outside Windhoek in Daan Viljoen Reserve to make boxes for small, hole nesting owls e.g.. African Scops-owl [ Otus Senegalensis ].To their surprise they not only had Scops and Pearl-Spotted owls using these but also Hornbills. ( Two illustrations B+W of box measurements and box in a tree)

Scops box Nam

Nest box dimentions




Diagram of African Scops-Owl nest box and a used one attached to a tree
I suppose that African Barred owls [Glaucidium capense ] and African Wood- owl [ Strix woodfordii ] could also use similar but slightly larger boxes, if they were put up in habitat where they occur.
Spotted Eagle-owls , are much easier , as they take anything , even a flower pot used on a porch or window ledge, as long as it looks like a tray or an open box with lots of space (see picture from Stellenbosch University).




 Box Stellb Univ






Owl box in a tree , for Spotted Eagle-Owls
Verreaux’s Eagle-owl [Bubo lacteus ] have the habit of taking over other raptor nests , e.g.. Wahlberg’s Eagle , in their off-season. So far I have no knowledge of these bigger owls making use of man made nesting platforms. The same goes for Pel’s Fishing-owl[Scotopelia peli ], they prefer to use a big hollow in a tree or nook where big side branch has broken off.( See article on Blackinstonia’s Fishing –owl for nest boxes in Japan ?)






POISONS , especially Rodenticides,  and poisoning are the biggest issue , especially where rodenticides are used to protect crops. Rats, mice and other mammals raid crops and are killed by poisons , then owls prey on these poisoned animals , and then they die of secondary poisoning!





SEO Racumin Advert Racumin_poison

Deadly collection of poisons, in a shop, not all suitable for use. Racumin , a more safe poison to use
Even using “safe” poisons , e.g.. Racumin (Bayer) can be harmful [ see article “On the Farm” Internet] The “Safe “ poisons has to be consumed in such large doses to be effective in killing the target prey, that their bodies contain such high concentrations of poison by the time they die, resulting in owls and other non-target raptors being killed .
According to Quartus Laubscher , that implemented owls, as rodent control, on his farm for years (from1997) , his use of poisons has changed from a stream of poison flowing into the habitat , to just a small trickle.(Country Life April2011).
Using poisons brings with it a huge responsibility , e.g.. keeping it under lock, removing excess, and presenting it in correct dose and manner to the target prey. Furthermore prevent accidental contact by children and pets.
Remember there are birds that are day-time hunters e.g.. Black-shouldered kites and falcons. They also prey on rodents, like the Three-striped Mouse which is active during the day.
Conclusively I want to remind you that the next time you see an owl or raptor hunting, they are our allies in protecting our planet and also fighting the spreading of diseases to mankind.
Please help to protect our heritage – it cannot be replaced.


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