Poor designs, construction, and materials used to make barn owl boxes lead to a multitude of issues for owls. Owls will often inhabit less than adequate boxes driven by instinct and desperation to nest. It’s tempting to believe that the boxes must be good if a bird is nesting in it, but this isn’t necessarily the case. Since barn owls are cavity nesters who are also facing the additional issue of habitat loss, often the owls have no choice but to inhabit a poorly designed box. This causes a variety of problems, including:
Boxes that are too small.
Boxes that are too small will not be able to comfortably accommodate a brood of young birds. Barn Owls have the potential to lay 2–18 eggs, although typically 5–7 is the average number of eggs in a clutch. Since the owlets stay in the box until they are about 9-10 weeks and increase in size, it is imperative that the box be large enough to accommodate multiple owlets with the mother. Ideally, nest boxes should be at least 16” deep, 24" wide and 22"+ tall – minimum. This is because the owlets require ample space to stretch out and engage in activity to strengthen their wings so they can fledge successfully.
Boxes without a maintenance hatch.
A family of barn owls, with exception to the male owl and towards the end of the owlets’ development, the female too, will roost in a location near the nest, often in trees and other barn owl boxes close to the nesting box, while their owlets remain in the same box they hatched in for the whole season. This means that the debris from the owls, such as pellets, excrement, even dead remains, etc., stay in the box.
Investing in a box with a maintenance hatch should make annual box maintenance safer, faster and easier for the technician doing the work. Boxes that do not give access to the inside for seasonal cleaning, can quickly become filled with waste, possibly causing health concerns for the owls and greatly contributing to the deterioration of the box itself. Owls will return to nest in familiar boxes regardless of debris pileup, which can cause serious health concerns for the whole owl family over time. Choosing boxes that are easy to maintain, will assure the owls a safe and healthy stay during the time they occupy the box and cleaning will be much easier and also ensure your boxes last for many years.
Although last on the list of concerns for owls, human safety is a significant factor that contributes to the well-being of barn owls. If the box is so high off the ground and it puts humans in danger, it is more than likely the barn owl boxes will never be cleaned or maintained. Studies show that barn owls prefer nest boxes at least 10 feet off the ground, but did not show strong preference for heights greater than that. Since maintenance of a barn owl box should be done annually at the end of every nesting season, it is important to have the barn owl box height no higher than 15 feet. We recommend 10 to 15 feet.
Solution: It is our hope that after spending some time on our website that you will gain a solid understanding of exceptional barn owl box construction. Ideally, nest boxes should be at least 16” deep, 24" wide and 22"+ tall – minimum. This is because the owlets require ample space to stretch out and engage in activity to strengthen their wings so they can fledge successfully. Barn Owl Boxes purchased through members of The BOMP Coalition Project will meet these important criteria.
Barn Owls face a variety of serious threats that are not widely known because they are nocturnal and seen infrequently. These dangers can be eliminated by educating yourself and using proven solutions to help support them. The threats and dangers are listed below from the most urgent, to the most concerning.
Poor Box Design
Rat poisons are a common tactic used by people who are having issues with rodents. The most serious of these substances are called second-generation anticoagulant rodenticides (or SARs) containing the active ingredients brodifacoum, bromadiolone, difethialone and difenacoum. These can only be used legally by licensed applicators (professional exterminators). Strychnine is used as a rodenticide, but can only legally be used to control pocket gophers and must be placed underground in gopher burrows. Strychnine should not be used to control mice, rats or ground squirrels. Any above-ground use of strychnine may lead to unintentional poisoning of wildlife and pets. Often, people using these chemicals don’t know of the dangers they are causing to owls and other raptors, wild mammals, and pets.
Rodents consuming these poisons typically do not die until several days after feeding and may continue to ingest more poison. The poison is then available to a predator or scavenger that eats the rodent. If the exposed rodent does not die, the poison can persist in its body for several months, and any animal that eats the rodent will ingest the poison. This is called “secondary” poisoning.
Many of the wildlife professionals in our Coalition report getting intakes of owls and other large raptors who, for all intents and purposes, have a healthy body composition, are strong, and have no sustained injuries. Intakes like this go rapidly downhill because of secondary poisoning – they’ve eaten a rodent who was poisoned. It is important to understand the risks to birds, and many other mammals, when deciding how to control rodent populations.
Remember, barn owls, in a single night, can catch many rodents hunting. By poisoning the rodents (and therefore the birds), you’re eliminating a major resource and organic method of rodent control. Even more concerning, the parent owls are also bringing back poisoned rodents and feeding them to their owlets.
Although our Coalition members who run a BOMP program may consult, research, and perform maintenance, none of our BOMP members will install barn owl boxes where known rodenticides are being used. One of our main goals is to help reduce the use of rodenticides. It would be highly unethical for any of our members to install a barn owl box in a location they know is using rodenticides.
Solution: The first step to minimizing and eliminating the use of rodenticides is to educate yourself, your neighbors and your community about the important ecological role these birds of prey play in urban and wild areas. It’s equally as important to gain an understanding how damaging these products can be to pets, children and wildlife alike. In becoming a visitor to our website, you have already taken the first step in becoming a part of the solution.
Habitat loss -- including the loss of trees used for nesting, shelter and rest, and the loss of grasslands and oak savannah -- is making it challenging for barn owls to find adequate areas for nesting, hunting prey, and raising their young. The BOMP Coalition is striving to remedy these ongoing issues with our Barn Owl Maintenance Programs. These birds are cavity nesters and instinct drives them to search for and locate much needed places to lay their eggs and raise their young. Because of the expansion of urbanization, there has been a significant drop in nesting areas such as old barns and big trees with cavities and crevices, and our cutting edge barn owl box design, when placed in relevant locations, can help boost and maintain barn owl populations in local communities. Studies show that barn owls are more likely to occupy a nest box when there is natural habitat nearby. And owls nesting in boxes and tracked with GPS were found to hunt in nearby grasslands and other natural habitats, in addition to agricultural areas. Therefore, the conservation of natural habitats such as grasslands, oak savannah, and forests can help ensure barn owls will nest in boxes and hunt for rodent pests. Installing our barn owl boxes in specifically chosen locations on your property, effectively encourages a nesting opportunity, thereby significantly contributing to the success of barn owls overall.
Solution: One way to help barn owls is to leave an old barns and sheds available for nesting or roosting owls if possible. If this can’t be done, you can instead recreate a space within a new building that owls can safely use. You can also install barn owl boxes on your property with the help of a BOMP Coalition Member. Appropriately placed barn owl boxes are an effective strategy for recreating nesting opportunities because boxes mimic the nesting habitat these owls instinctually seek out.
Some boxes, if mounted where predators can access them, become a problem in and of themselves. Even though barn owls are birds of prey, it’s important to also recognize that these birds have predators. It is critical that when deciding where to place barn owl boxes, an awareness of how a predator could access the box be considered. Boxes that are placed in trees, on barns, or on other structures that predators like raccoons and opossums can climb are potentially open to predation. We recommend mounting your box to a high, slick, metal pole that would be difficult for a predator to grip and climb. It’s also important to place the box away from trees or any other high object that could grant a predator access by climbing and jumping to the box. Our team of wildlife professionals can assist you in choosing the perfect location for your barn owl boxes.
When it comes to predation, it’s not only where the box is placed that should be considered. Equally important is the size of the entry hole. You may not think that something as simple as an entry hole could be so important to owl box design; however, proper placement of the entry hole is imperative to the safety of the owls. In order to deter potential predators, the entry must be at least 4" but no greater than 6”. We designed our entry holes in a unique “oval” shape that ensures Great Horned Owls can’t be granted access, while still allowing entry to the barn owls. Our boxes also have a security shield installed inside. This ensures that the owls will have a place of refuge should Ravens and Hawks poke their head in to investigate. Placing the hole at least 16 inches high from the bottom of the box ensures that there will be adequate protection from rainwater, falling from the box, or being pushed out.
Solution: Purchasing your box through a member of The BOMP Coalition Project will ensure that your box will meet predator-proof criteria. In addition, you will be working with wildlife professionals who will be able to assist you with box placement and consult with you on potential threats in regard to predation. Should you decide to purchase through another vendor or build your owl box, we recommend you consider all the information in this article. Avoiding adding perches to your box, adhering to entry hole recommendations, and using a pole mounted box are all critical factors to consider in your purchase and/or building plans. There are some “hawk perch” styles of barn owl boxes out there that are attached, or, in close proximity to, the nest box. This style should never be used, as it attracts hawks to sit and become accustomed to this perch for hunting. The problem with this is that the owlets inside the box will vocalize and attract the predator instincts of the hawks. Once the owlets begin to fledge, they are easily preyed upon by hawks that have grown accustomed to this perch and are waiting for the opportunity to catch the “easy” prey.
Challenges Owls Face
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