Owls in agriculture

Barn Owls vs rats and mice

• 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 Verreaux's eagle (Aquila verreauxii) 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 their foraging endeavours. This control reduces food availability and in turn, reduces the population. (Davies, PhD. thesis)

How it works

• 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.

Implementation

• 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.).

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Owl boxes

• 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 manufacture have a sliding door on the breeding chamber and we use this 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.

What to expect

• 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. A well managed owl project can respond to rodent eruptions, provide information on rodent diversity and exert significant pressure on rodent species currently impacting crop yield.
• Eco-Solutions is involved in numerous owl box projects and are 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, serviced and managed owl boxes. Through pellet analysis (picture alongside), it was established that these Barn Owls collectively consume more than 9000 rodents per annum.

Lets do it?

• 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 visit our FAQ section here.
• EcoSolutions manages integrated pest management projects both nationally and abroad. We undertake remote consultations using google imagery where we plot optimum owl box placement sites. We deliver and install owl boxes countrywide. The key to a successful owl box programme is correct site selection and maintenance and management. To find out more:

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