Owls and Integrated Pest Management

Barn Owls (Tyto alba): a natural ally in the control and management of rodents

The idea of harnessing Barn Owls (Tyto alba) in an attempt to control rodents is not a new one. The first introduction of this species for that purpose can be traced back to 1899 when seven birds were imported from London by the Otago Acclimatisation Society and liberated at West Taieri in New Zealand. This attempted introduction did not work and these owls were not recorded after 1900. Barn Owls were also released in an effort to control rodents between 1910 –1960 to the Seychelles; Bermuda; Tasmania; St Helena and Hawaii. In South Africa the Barn Owl is a common resident to most parts of the country, so the issues relating to re-introduction are interesting, but not necessarily applicable.

Barn Owls are specialised rodent hunters. They are one of the few predatory species that have the ability to dramatically regulate their clutch size in a response to eruptions in the population of their prey.  When a rodent explosion occurs, Barn Owls are capable of producing “super clutches”. The healthy condition of the female owl allows her to lay anything from 8 to 20 eggs in a clutch and, as found in the Malaysian Palm groves, Barn Owls are capable of raising two clutches per year. In years in which rodent numbers decline, the clutch will be smaller.  The growth rate of a young owl is very fast. From hatching to flight takes about 40-50 days and in this time the young owl’s food requirements are enormous. An owlet can easily consume 2-3 rodents per night. Parent owls will continue to provide food even when the youngsters are satiated. It is not uncommon to visit occupied owl boxes and find a larder of dead rats cached in some corner. The relationship between predator and prey is always a complex one; in many cases, it is not just predation that controls the prey, but the behavioural adjustments required by the prey in order co-exist with the predator. The control of Rock Hyrax (dassie) numbers by the Black Eagle is not related as much to the number of hyraxes caught by the eagles, but to the reduction of foraging freedom created by the presence and the potential threat of predation by the eagles. The presence of an occupied eyrie prevents the hyrax from straying too far from the rocks in its foraging endeavours. This control reduces food availability and in turn, reduces the population. (Davies, PhD. thesis)

Barn Owl projects have been implemented in many countries worldwide. The Malaysian palm grove projects were well documented in a doctoral thesis and dealt with the financial comparisons between baiting and owl boxes. Over a seven-year study, it was found that 75% of the 275 owl boxes erected were utilised. The reduction in rodent damage was reduced by 62% and the use of poison eradicated. The boxes were placed at a ratio of one per 5ha stand and the cost of maintenance and construction was recouped within the first 5 years. The occupancy rate of the owl boxes was fascinating and endorsed the concept of “natal recognition” amongst owl species. Natal recognition is the desire in young owls to replicate the breeding site in which they were raised when they too reach breeding maturity. In the Malaysian project the first year produced an occupancy rate of just 7%; in year 2 this increased to 17%; by year 3 it had risen to 30% and in year 4 it climbed dramatically from 30% to 62%. This huge increase in occupancy can be explained through the collective young from the first three years reaching adulthood and actively searching out owl boxes to breed and rear young of their own. Similar trends have been experienced in the Everglades Barn Owl Project undertaken by the University of Florida.        

The occupancy of the owl boxes and the production of young is directly related to rodent numbers. The size of a territory held and defended by an owl pair is governed by the prey availability required by that pair. In years where rodent numbers are high, territories will be smaller, while the converse is true when rodent numbers diminish.

The implementation of a rodent control program through the erection of owl boxes is a relatively simple undertaking. EcoSolutions always recommend placing owl boxes at farm villages and schools as these are always areas where rodent numbers are high. The education required by the farming community can also begin at these sites. In addition to schools and dwellings, boxes should be positioned near areas where rodent damage is highest. (feedlots; stables; certain crops etc.) The box itself is easily constructed and a search on the internet will provide various owl box designs.

When erecting boxes it is important to work on a minimum height of 3 meters - this will prevent predators from gaining access to the box.  In addition, the boxes should be placed on the edge of fields, or at a point where a mosaic of different habitats occur. Barns and old abandoned buildings are excellent places for barn owl boxes.  The placement of boxes quite close to a farm road or track is ideal; this allows for easy access when checking, cleaning and also where the ringing of young owlets is undertaken. The owl boxes we use have a sliding door on the breeding chamber and it is this door we use to access the chicks or clean out the box. The inside of the breeding chamber should be lined with a pea gravel substrate. Pea gravel allows for better drainage and is less prone to bacterial build up. In boxes without substrate, owls will regularly use their regurgitated pellets to line the nesting cavity. An owl produces an indigestible pellet on a daily basis. This is comprised of the bones and fur of its previous night's catch. These pellets are great for ascertaining rodent data as well as providing fascinating educational props for kids and biology classes where they can be dissolved and studied. The owl box should be cleaned after each breeding cycle. It is a good idea to wait at least a month after the chicks have fledged before spring cleaning as young birds will usually sleep in the box during the day until they have become fully independent.

It needs to be remembered that Barn Owls will never completely eradicate rodents within farmlands, but a well implemented Barn Owl project can reduce rodent damage to manageable levels in a sustainable and responsible manner.

Eco-Solutions is currently involved in numerous owl box projects and is able to provide suitable boxes as well as advice, box installation and project monitoring (ringing chicks, GIS etc). An EcoSolutions owl box project in Irene, Gauteng currently has 12 occupied owl boxes that we service and manage. Through pellet analysis, it was established that these Barn Owls (Tyto alba) collectively consumed more than 9000 rodents in 2016.

For assistance in setting up owl boxes as a viable component to an integrated pest management programme (IPM) please feel free to contact EcoSolutions at info@ecosolutions.co.za or visit our website at www.ecosolutions.co.za  If you wish to read further on owl box location, orientation, occupancy etc. please follow the link provided.
http://ecosolutions.co.za/news/autumn-newsletter-2017

 

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Reviews

Karen Stander
Our box have a spotted eagle owl! We stay on a smallholding in the Chancliff area, Krugersdorp and discovered that our recently serviced owl box, has a long awaited inhabitant! So glad and thankful to have the privilege of sharing our piece of nature with hopefully a breading pair soon! Have to tell you the bats are also happily occupying their box!

Cheryl Siewierski
Brilliant service from hugely knowledgeable installers at our home in Harties this morning. We are thrilled with our new bat and owl boxes and sure the residents of these will be too! Excellent to know that EcoSolutions also monitors numbers and patterns of the owls in perpetuity. Thank you!

Beryl Scott-Payet
Fantastic, thanks to all at Eco Solutions for your support and help with Strix (our injured owl) and the installations of the boxes and houses at Steyn City.

 

Owl Ring Recoveries


 

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