Barred owls (Strix varia) are medium-sized owls native to North America. They are highly adaptable birds that have expanded their range dramatically over the last century. Barred owls nest in natural tree cavities but will also readily use artificial nest boxes intended for other species. The use of nest boxes by barred owls has implications for forest management and conservation of cavity-nesting species. This article explores the key questions around barred owls’ use of nest boxes:
Do barred owls actually use nest boxes?
Yes, there is extensive evidence that barred owls will nest in artificial boxes. Studies have documented barred owls using nest boxes intended for species like wood ducks, eastern screech-owls, and American kestrels. Barred owls likely started using boxes opportunistically but have now learned to associate them as potential nest sites.
How often do barred owls use nest boxes versus natural cavities?
Barred owls show a preference for natural tree cavities for nesting but will readily use nest boxes in areas where natural sites are limited. One study in North Carolina found barred owls used nest boxes and natural cavities at approximately the same frequency in a managed pine forest. However, in another North Carolina study, barred owls strongly preferred natural cavities over nest boxes when given a choice.
What nest box designs and locations are best for barred owls?
Barred owls have been documented using a wide variety of nest box types, including boxes for wood ducks, kestrels, screech-owls, Northern flickers, and bats. They do not seem very selective. Boxes with interior dimensions of around 12″ x 12″ x 24″ are suitable. Barred owls prefer boxes placed high up, 15-30 feet above ground. They often choose boxes on the edge of open areas adjacent to mature forest.
Advantages of Nest Box Use for Barred Owls
Barred owls gain several advantages from using artificial nest boxes:
Earlier nesting
Nest boxes provide enclosed, weatherproof cavities available early in the spring. This allows barred owls to start nesting earlier than waiting for natural cavities to form in trees. Earlier nesting gives owl young a head start.
Lower predation
Nest boxes may provide more secure nest sites safe from predators compared to natural cavities. Boxes can be equipped with predator guards to prevent raccoons and other animals from entering.
Improved breeding success
As a result of earlier nesting and reduced predation, barred owls may fledge more young per nest when using nest boxes rather than natural cavities. One study found barred owl nests in artificial boxes fledged 3.0 young on average compared to 2.2 in natural cavities.
Expanded habitat options
Nest boxes effectively increase the number of potential nest sites for barred owls in an area. This allows barred owls to colonize and thrive in habitats like younger forests that lack natural cavities.
Disadvantages of Nest Box Use for Barred Owls
While nest boxes clearly benefit barred owls, there are some potential downsides:
Competition with other cavity nesters
Barred owls may compete with native species like wood ducks and screech-owls for nest boxes. Barred owls are larger and more aggressive, so can displace other species from their nest boxes.
Artificially inflated populations
An abundance of nest boxes may lead to higher densities of barred owls in an area than would naturally occur. This could negatively impact populations of prey species or lead to barred owl range expansion.
Disease transmission
Re-using nest boxes without disinfection could promote the spread of diseases like owl pox. Sick owls may also become concentrated around popular nest box areas.
Loss of natural behavior
Reliance on artificial nest boxes could cause barred owls to lose natural cavity nesting behaviors. This may have long-term impacts on population health and resilience.
Impacts on Other Cavity Nesting Species
The use of nest boxes by barred owls has significant impacts, both positive and negative, on other cavity nesting birds that also rely on the boxes:
Wood Ducks
Positive Impacts | Negative Impacts |
– Barred owls may chase away predators like raccoons that eat wood duck eggs | – Barred owls compete directly with wood ducks for nest sites |
– Presence of barred owls may indicate good nesting habitat | – Barred owls may take over or damage wood duck nest boxes |
Eastern Screech Owls
Positive Impacts | Negative Impacts |
– May benefit from barred owls chasing away predators | – Direct competition for nest cavities |
– Unlikely to co-occupy nest box with larger barred owl | – Barred owls may kill or consume screech owls |
American Kestrels
Positive Impacts | Negative Impacts |
– May have some protection from predators | – Much smaller kestrels excluded from nest boxes by barred owls |
– Kestrels may reuse old barred owl nests | – Risk of barred owls preying on kestrels and their young |
Northern Flickers
Positive Impacts | Negative Impacts |
– Flickers are large enough not to be displaced by owls | – Potential competition for suitable nest cavities |
– May benefit from reduced predators around owl boxes | – Risk of owls preying on flicker nestlings |
Overall, the use of nest boxes by barred owls has mixed impacts on other cavity nesters – providing some protection against predators but also introducing a powerful competitor. Careful management strategies are required to minimize conflicts.
Management Strategies for Nest Box Use by Barred Owls
Several management approaches can help mitigate issues arising from barred owls using nest boxes:
Site boxes to favor target species
Place nest boxes in locations and configurations that favor intended native species over barred owls. For example, install wood duck boxes over water.
Use exclusion devices
Modify nest boxes with size restrictions or barriers that exclude barred owls but allow smaller species access.
Add more boxes
Install supplemental nest boxes so there are adequate sites for both target species and barred owls.
Clean boxes annually
Clean out old nesting material each year to reduce parasites and diseases. Avoid re-using boxes where owls have nested.
Selectively remove barred owls
In high priority areas for species of concern, selectively remove barred owls that claim nest boxes.
Educate landowners
Encourage practices like proper box placement and maintenance to minimize conflicts.
Conclusion
Barred owls have shown an ability to adapt to using artificial nest boxes, with both positive and negative impacts. Responsible management strategies, based on open communication, coordinated research, and continuous evaluation, offer a path to balance the needs of barred owls and other native cavity nesting species sharing our forests and wetlands. With proactive policies, these remarkable birds can continue thriving alongside one another.