What is a Bluebird House Predator Guard and what types are there?

Bluebird house predator guards are tools that help prevent predators from entering a nest box. Three common predator guards are baffles, Noel guards, and hole extenders. Additionally, bluebird landlords may install other devices to prevent competing birds from evicting nestling bluebirds.

After decades of research and experimentation, bluebirders have tested multiple types of predator guards as well as designed special boxes that obstruct predator entry while still allowing birds to nest.

Other predator guards bluebirders use include conical (cone-shaped) squirrel baffles, metal hole guards and flashing around trees (not very effective).

Some predator guards are designed to keep out specific animals, while others are more broad-spectrum devices, effective against several types of predators.

Aside from predator guards, mounting a bluebird house to a tall pole (5.5 feet or higher) can also help deter predators when paired with the right guard.

Because there are so many types of predators that can invade a nest box, a more universal predator guard or guard combination is highly recommended.

Learn about 8 of the most common bluebird predators

List of common predator guards

• Stovepipe baffle
• Conical baffle
• Noel guard
• Metal flashing
• Metal hole guard
• Hole extenders
• Unique nest box designs

Among this list of predator guards, the most popular predator guard is the stovepipe baffle.

A second popular guard type is a metal hole guard or hole reducer. Usually, if a smaller bird such as a chickadee decides to nest in a bluebird house, bird landlords will add a metal hole guard to prevent bird eviction and aid the nesting bird’s survival.

The stovepipe baffle (8-inch x 24-inch, or 8-inch x 60-inch) is not only the most popular type of predator guard, when installed on a properly mounted nest box pole, it is one of the most effective predator guards out there.

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Are predator guards necessary for bluebird houses?

Predator guards are essential when housing bluebirds, tree swallows, chickadees and other cavity nesting birds. Unlike open nesting birds such as robins, cardinals, and house finches; cavity birds have no escape when a predator enters the nest box. They immediately become trapped.

While losing eggs or nestlings can be heartbreaking, there is a higher ecological cost when a predator takes the adult bird.

Cavity nesting bird numbers have already been on a decline, as we lose viable reproductive adult birds, there is a potential exponential loss involved.

As you journey into bluebird care and bluebird landlording, it is important to understand the responsibility that comes with job.

When attracting and housing bluebirds, we must prioritize their survival over our pleasure and think with a heart for conservation.

Nest box predators of bluebirds include raccoons, snakes, opossums, chipmunks, squirrels, cats and sometimes birds of prey.

Therefore, predator guards are vital when protecting and conserving our native cavity birds.

How does a bluebird house predator guard work?

How bluebird predator guards work depends on the guard itself. For instance, the wobbling element and the size of a stovepipe baffle hinders climbing predators. Noel guards and hole extenders put distance between the predator and nest box. And metal hole guards keep predators from widening the entrance.

Stovepipe baffles – One of the most common bluebird predator guards

A stovepipe baffle is a large, metal, cylinder shaped device that slides over a portion of the pole between the nest box and the ground. Appropriately sized stovepipe baffles prevent climbing predators, including snakes, from entering the nest box.

Learn all about stovepipe baffles

How to make your stovepipe baffle most effective

Stovepipe baffles are effective across a wide range of predators including snakes, raccoons, opossums, cats, squirrels, and chipmunks.

In order for your baffle to be effective, there are a few steps you should take.

1. Mount your nest box to a pole that is at least 5.5 feet tall.
2. Do not place your nest box directly under a low hanging tree branch where predators could jump from above onto the nest box.
3. Do not hang your nest box on a shepherd’s hook.
4. When choosing a stovepipe baffle, it is best to buy one that is 8-inches in diameter by at least 24-inches tall. Many bluebirders suggest making one that is 60-inches tall.
5. Your baffle must wobble. A wobbling baffle makes an attempted climb too unsteady for predators.

Cone Squirrel baffles – Cheaper but not very effective against bluebird predators

Cone squirrel baffles are wide, cone-shaped devices that fit around a pole, preventing predators from climbing and accessing the pole’s contents such as birdfeeders or nest boxes. While these baffles are somewhat effective for birdfeeders, they are not effective enough when protecting bluebird houses.

Cone-shaped squirrel baffles were designed to keep squirrels off birdfeeders. If you have had experience with squirrels, you understand how hit-or-miss these types of baffles can be. Squirrels are relentless problem-solvers when it comes to food.

Since these baffle types are minimally effective at protecting birdfeeders, they’re not going to be protective enough when it comes to the life of an incubating mother bluebird or her nestlings.

Utility buckets as baffles as bluebird predator guards – not recommended

Some people modify large hardware buckets into baffles by turning them upside down, cutting a hole in the center and mounting it to a nest box pole. However, experienced bluebird landlords and trail managers do not recommend this because bucket baffles are not long enough to prevent predators.

The bucket baffle works like a stovepipe baffle in that it is tube shaped and very wide. When mounted to a pole in such a way that it wobbles if it were climbed, it might be effective against small predators such as squirrels and chipmunks.

However, buckets are not long enough to stop raccoons and snakes which are a significant threat to anything inside a nest box.

Further, these buckets have multiple lips which can aid snakes in gripping and climbing up the baffle itself and entering the nest box.

Metal flashing as bluebird predator guards around trees

Flashing used as predator guards is made of a thin, flexible metal sheet. The sheet is wrapped around a tree beneath where a bluebird house is placed and acts as a baffle that makes it hard for predators to climb and reach the nest box.

While metal flashing is not a very effective bluebird predator guard, when a bluebird house is mounted to a tree, any means of protection is vital.

Anyone working with bluebirds or wanting to start out with bluebirds are strongly advised NOT TO MOUNT BLUEBIRD NEST BOXES TO TREES.

Improper mounting to trees, wooden posts and fence posts is offering up animals as temptation to predators. And while you may not have seen any of these predators, don’t think your backyard doesn’t host them.

Many bluebird predators are nocturnal and very stealthy at night. It is likely you’ll never see one, but they’re there.

With that in mind, if you’ve set a bluebird house up on a tree and are in the middle of an active nesting period (eggs are laid, mother is incubating, or nestlings present), putting up flashing may actually save their lives until you have the ability to properly mount the box.

Another protective option is a Noel guard. When in combination with metal flashing, your birds have a better chance of survival until you can remount the nest box.

Noel Guards – Caged bluebird house predator guards

Noel guards are a wire mesh structure, shaped like an open cage that fits around the nest box entry hole and creates distance between a mammalian nest box predator and the entrance. The edge facing out has sharp wire points that jab and deter reaching predators.

Learn all about Noel guards and when to use them

Noel guards are a fairly effective form of predator guard against mammalian predators such as squirrels, cats, raccoons and opossums. In addition to larger mammals, they are effective at preventing larger birds from reaching into the bluebird house.

However, Noel guards are not effective against snakes (a common bluebird predator) and chipmunks. Both are able to easily crawl through.

While these predator guards are fairly effective, they are not nearly as stovepipe baffles. This is because stovepipe baffles protect a wider variety of some of the most common nest box predators (racoons and snakes being two of the usual suspects), as well as cats, chipmunks and squirrels.

Times when a Noel guard might be helpful is when your nest box is mounted to a fencepost, tree or wooden post.

Something important to note about Noel guards is that they are not always accepted by the resident bird. If you have nesting birds, you will need to watch intently to make sure they accept it.

Metal hole guards – prevent entrance widening and bird eviction

Metal hole guards for birdhouses are thin metal rings with a hole in the center. They fit around a nest box entrance and prevent animals from enlarging the hole. Additionally, they can be used to make an entry hole smaller, allowing smaller birds to nest without eviction.

What happens often is that certain animals will gnaw around the nest box entry hole, making it easier for them to enter. It also damages the box over time.

Metal hole guards are a way of preventing birdhouse hole enlargement.

Squirrels, raccoons and chipmunks all will try relentlessly to access food in the nest box, but woodpeckers are another animal that might try to widen the hole and ruin the box.

Hole size reduction is another important use of metal hole guards. For example, a 1-1/8 inch hole guard placed over a 1-1/2 nest box hole makes a bluebird house safer for chickadees.

Chickadees often run the risk of being evicted by larger birds like bluebirds. They also exclude house sparrows and starlings – invasive birds that kill native cavity birds for nesting sites.

Learn about caring for nesting chickadees

Hole guards do not prevent mammalian predators and snakes from reaching into a nest box. They simply prevent animals from enlarging the hole. More technically, because they’re made of metal, they allow bird landlords control over the nest box’s hole size.

Hole extenders – Nest box tube entrances

Nest box hole extenders are usually tube-shaped predator guards that fit around the birdhouse entrance, extending the hole, and providing more distance between a predator, as well as obstructing the reach of a nest box predator.

While hole extenders are a cheaper predator guard type, and are effective against mammalian predators, they will not prevent snake.

Another problem with hole extenders is birds often do not accept them, and therefore, we do not recommend these.

Other types of nest box guards – wren guards, sparrow spookers and monofilament line

Additional bluebird house guards include wren guards, sparrow spookers and monofilament line (fishing line). These objects are meant to deter both native and invasive competing birds from evicting or even attacking and killing bluebirds for their nest boxes.

Bluebird house guards to prevent competing birds:

• Wren guards
• Sparrow spookers
• Monofilament line (fishing line)

Wren guard

A wren guard is a hood-like device that fits over a bluebird house or bird nest box and hides the appearance of the entry hole. The purpose of a wren guard is to prevent house wrens from overtaking and harming eggs and nestlings of an occupied bluebird house.

Learn to keep the peace between house wrens and bluebirds.

Because house wrens make their nest from small twigs and sticks, another advantage of a wren guard is it creates more of an obstacle for house wrens that might try to build in an occupied nest box.

As far as effectiveness, wren guards are most effective when a house wren has not yet been in the nest box. If a house wren has previously visited a bluebird house, he may become more persistent, even after the wren guard has been added.

Despite this, we still suggest adding a wren guard to protect your bluebirds or other native birds who are currently nesting in a box.

There are also times that wren guards fail, especially during years of heavy competition or in locations experiencing heavy competition.

Wren guards should be added after the first egg is laid (no matter the bird type). Chickadees and bluebirds both tolerate wren guards. However, it is a good idea to watch the nest box intently to make sure your bird has accepted the wren guard (gotten inside the birdhouse after the wren guard was added).

Once you’ve seen both parent birds get into the nest at least once each, you can trust that they’ll be able to continue to access their nest.

Making a wren guard is very easy, and they can be made from cardboard. The benefit of a cardboard wren guard is they’re easy to manipulate if needed and can usually hold up for the current brood.

If you do use a cardboard wren guard and it rains heavily, be sure to check it and replace it if it is limp, sagging or waterlogged.

Sparrow spooker

Sparrow spookers are devices made of a rack and metallic streamers that fit on top of a bluebird or chickadee house. They are meant to scare off house sparrows, an invasive bird that would otherwise kill the native bluebird or chickadee for their nest box.

House sparrows are a critical problem in North America. They have proliferated in such high numbers and outcompete native cavity birds to a point where certain cavity species, such as purple martins, are almost entirely dependent on human help for survival.

One of the ways bluebird landlords deter house sparrows is by using sparrow spookers that fit on top of the nest box.

There are a few important things to help optimize your sparrow spooker:

1. Make sure the streamers brush the top of the roof and hang over the entry hole just a little bit.
2. Streamers must be made of a metallic ribbon material. Satin or duller type material will not be as effective.
3. Sparrow spookers should be added after the first egg is laid.
4. If a house sparrow has already entered the box once, a sparrow spooker most likely will be ineffective.
5. Sparrow spookers should be combined with responsible trapping. While they can be effective, during periods of heavier competition, they only buy time.

We recommend the use of sparrow spookers in all cases. Even if you haven’t seen a house sparrow around, a single male can sometimes show up, scouting your box and killing anything inside, including adult birds.

Just make sure to add the sparrow spooker after the first egg is laid.

Just like with wren guards, sparrow spookers can be made. Several bluebird landlords have found creative ways to rig up a sparrow spooker.

One simple way to do this is to use a pasta rack and add streamers to it. We have an easy-to-follow video on that.

Monofilament line (fishing line)

Six-pound monofilament line, or fishing line, can be added to the sides – 1/8 of an inch away from each side of a bluebird house’s entry hole to deter house sparrows. For many bluebird landlords, this has been an effective method of house sparrow deterrent when combined with responsible trapping.

In our experience, this has been more effective against house sparrows, though it is not 100% effective. It is also ineffective against Eurasian tree sparrows (house sparrow cousin).

We have a video about how to add monofilament line to a nest box. You can also find several plans out there illustrating how it is applied.

Where to find predator guards

Most of the predator guards discussed can be conveniently found on Amazon*, through other bird websites, or they can be made. We’ve compiled a list to help you find what you need, and we also put out our recommendations.

Stovepipe baffles

An 8×24 inch stovepipe baffle can be found on Amazon. These baffles are effective against most predators as well as smaller snakes.

Larger baffles must be made. You can find a tutorial here: https://www.youtube.com/watch?v=gaS7r9ZIrU8

Nest Box Pole Kits

It’s important to mount your nest boxes to a sturdy pole. When looking for pole kits, the best ones are going to have a built-in auger.  We have some recommendations that are available on Amazon, and we have tested these products too.

The Droll Yankee Pole System is a kit that will have a little bit more than you need. However, it is an extremely sturdy pole, and one that is easy to drive into the ground and work with.

The Universal Mounting Pole kit is a more affordable option. This one is pretty sturdy and fairly easy to work with. However, if it is not driven deep enough into the ground, it may lean. In a heavy thunderstorm, it may lean even more. If you are using a heavier nest box, we recommend you consider the Droll Yankee option instead.

Noel Guards

Noel guards can be made, and we have a really helpful printable template that you can use right on top of the hardware cloth to know exactly where to cut.

However, given the cost of hardware cloth and the hassle of using it, we recommend ordering a Noel guard instead of making one. It’s only ideal to make one if you already have the hardware wire available.

Hole Reducers / Hole guards

When working with chickadees and house wrens, a 1-1/8-inch hole reducer is a vital protective guard because it prevents nest box eviction.

When working with eastern bluebirds, a 1-1/2-inch hole guard will prevent hole enlargement.

Nest box hole extenders

Hole extenders are not recommended as highly because birds sometimes struggle to accept them. They can create a lot of obstacles for fledging and parental access. Your best bet instead of these is a good baffle.

However, if you have your house improperly mounted (tree, fence post, fence or wooden post), a hole extender might help you safely ride out this nesting cycle until you can remount it.

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