There is a lot to learn about eastern bluebirds once you get your first pair to nest in your birdhouse. It can be overwhelming, and some of the information isn’t easy to find. Perhaps one thing you’ve noticed are different baffles. But what all do you really need to protect your bluebirds from?
Eastern bluebird predators threaten eggs, nestlings, and adult birds. These predators include raccoons, feral cats, squirrels, black rat snakes, kestrels, and hawks. Furthermore, bluebird lovers should be aware of invasive competition species such as house sparrows and European starlings.
Despite the list of predators, there are a few things to keep in mind:
- There are ways to protect your birds, and we’re going to make it easy explaining this.
- There is a lot of front-end work, but once that is done, predator management becomes easier.
- One of the most universal ways to protect your bluebirds from predators is to use a stovepipe baffle. An 8 inch x 24 inch will work for most situations, but making your own that is longer (about 5 feet) adds even more protection.
- Part of being a bluebird landlord is coming to terms with conservation. And nature is nature. As heartbreaking as it can be, you do what you can, but remember that there is an unspoken balance at play, that must be at play for everything to work right.
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We’re going to run through the list of bluebird predators, competition birds, and other threats. Then we’ll provide an easy reference to help guide you in deciding how to protect your bluebirds.
| Eastern Bluebird Predators | Threat level | Protection Measure |
|---|---|---|
| Raccoon | High threat of predation | Stovepipe Baffle |
| Snake | High threat of predation | Stovepipe Baffle |
| Opossum | High threat of predation | Stovepipe Baffle |
| Chipmunks | High threat if in your yard | Stovepipe Baffle |
| Squirrels | High threat of predation | Stovepipe baffle |
| Outdoor Cats | Fairly high, especially for fledglings | Stovepipe baffle |
| Hawks & Birds of Prey | Medium threat. Concern for fledglings | Noel guard |
| Bears | Low threat level. Can wreck boxes | Reinforce pole |
Learn about different types of bluebird house predator guards
Article Contents
- Raccoons
- Snakes
- Opossums
- Chipmunks
- Squirrels
- Cats
- Raptors
- Bears
- Invasive Competition
- Native Competition
- References
List of Eastern Bluebird Predators
1. Raccoons (Procyon lotor)
Raccoons are native to North America and can be found all over the continent, with exception to certain zones. Raccoons will not only eat eastern bluebird eggs, but also nestlings and adult birds. These predators can reach into nesting cavities and capture roosting and brooding birds.
One study presented eastern bluebirds with four different dummy predators:
- a rubber black snake
- an American kestrel study skin (similar to, but not quite the same as taxidermy)
- a taxidermy mount of a raccoon
- a taxidermy mount of a chipmunk
Researchers recorded bluebird responses when presented with each predator. Every time bluebirds were presented with the raccoon, bluebirds responded with an alarm or chatter call of a longer duration. Bluebirds did not always respond when presented with a snake, chipmunk or kestrel (the study also used a mourning dove as a control) (Grabarczyk, 2014).
You can protect bluebirds from raccoons with a stovepipe style baffle at least 8” in diameter and 24” tall. You can also use a Noel guard, which is a four-sided cage made of hardware wire (metal mesh) that prevents raccoons from reaching into the nest.
We have a guide on the best baffles to protect your bluebirds. For a commercially available baffle, we recommend this one from Amazon*
There are a few drawbacks to the Noel guard. First, they aren’t an absolute protector. So if you’re using a Noel guard*, it’s still a good idea to have a baffle. Second, bluebirds or other native cavity nesters might have trouble with the guard. It is better to add a Noel guard to your bluebird nest box after the first egg has been laid and monitor your bluebirds in case the Noel guard creates too much of an obstacle for them.
Learn more about Noel Guards in this detailed guide
Learn more about stovepipe baffles in this guide
Another important factor when protecting your bluebirds from raccoons is where your nest box is mounted. Birdhouses mounted on wooden fence posts or on trees are more at risk despite protective measures. Additionally, baffles cannot be used to protect them because they can’t be fixed to the mount.
It’s best to mount your bluebird box to a metal pole. Many bluebirders use EMT conduit to mount their bluebird nest boxes. This can be found in the electrical section of a hardware store.
However, if you don’t want to fuss with rebar and drilling into the conduit, there are commercially available poles that have an auger to drive the pole into the ground and a mounting bracket to easily mount the box. You can find one on Amazon*. And below is a link to a stovepipe baffle found on our site, which is the right size to protect against many predators.
2. Snakes: Rat Snakes, Coachwhip Snakes (Pantherophis obsoletus, Masticophis flagellum)
Snakes have caused heartbreak for many bluebird trail monitors. However, they are important to our ecosystem and native. They should not be killed if discovered in a nest box.
Snakes will eat eggs, nestlings and adult birds. They are able to easily climb birdhouse poles and climb into a nest box. Bluebird landlords should always take caution when monitoring a nest box because there is always a possibility of a snake or other organism being inside.
Unfortunately, upon discovering a snake in a nest box, many newer bluebirders will kill them. This is due to a natural desire to want to protect the bluebirds they’ve invested in as well as a lack of understanding. Rat snakes, coachwhip snakes and other snakes that might prey on nestlings are native to the United States. There are very few exceptions to this.
Furthermore, these snakes serve a vital purpose in our ecosystem, such as keeping rodent populations down. Rat snakes also kill the venomous copperhead snake. So it’s important as a birder to understand the balance.
You can protect bluebirds from snakes by mounting your bluebird box on a metal pole. Stovepipe baffles offer great protection, but larger snakes can still climb. In this case, an 8” by 5’ baffle is recommended.
While a Krueger trap is recommended for purple martins, they are not widely recommended for protecting bluebirds, chickadees, tree swallows and other cavity bids.
For clarity, the Krueger snake trap is made of a metal ring that serves as the base of the trap. Garden netting is then gathered around the ring on one end and bunched together at the top. The result looks conical, much like a hoop skirt made of garden netting rather than fabric, and not nearly as wide around.
Traps are placed below purple martin houses, and snakes that climb the pole end up tangled in the netting. Again, if you use this type of trap, it is critical you are checking these traps often so you can release the snake immediately. Trail cameras help in these instances.
In the case of bluebirds and other cavity birds, a wide baffle offers significant protection from snakes.
Please never assume you do not have snakes in your area. This is a dangerous misconception a lot of people have, which leads them to dismiss important protective accessories. Later, they discover snakes are in their area after their nest box has been raided.
Save yourself the heartbreak and at least get an 8” stovepipe baffle installed. You can find our tips on baffles here, and you can find commercially available baffles here on our site. Please note, the 8” x 24” baffle will only protect against snakes smaller than 5 feet.
Finally, a Noel guard is not sufficient protection against snakes.
3. Opossums (Didelphis marsupialis)
The common opossum, like other climbing mammals are predators of bluebirds, nestlings and eggs. They are able to reach into a nest box and snatch nesting birds and eggs.
If you know that you have an opossum in your yard or along your trail, it’s time to take protective measures.
A wide, long stovepipe baffle is one of the best ways to protect eastern bluebirds from climbing mammalian predators including opossums. Additionally, a Noel guard around the birdhouse entrance can help prevent opossums from reaching into the nest.
Only mount the Noel guard after the first egg has been laid. And watch your birds in case the guard is too much of an obstacle for them.
Make sure your nest box is mounted properly on a metal pole. Some bluebirders use grease on the baffles and poles for added protection against climbing predators.
4. Chipmunks (Tamias)
Chipmunks are a surprising eastern bluebird predator. Because of their small size, chipmunks are able to crawl into a bluebird house and eat eggs and nestlings.
Proper birdhouse mounting on a metal pole will minimize the chances of chipmunks getting into the nest box and eating nestlings or eggs. However, the best way to protect your bluebird house from chipmunks is with a stovepipe baffle that is at least 8” x 24.”
While a Noel guard offers some protection from chipmunks, they are not 100%. Adding a stovepipe baffle is going to be the best protection.
You may want to also consider adding a metal hole guard to your birdhouse to prevent chipmunks or other animals from gnawing away at the hole, enlarging it.
All of these protective items are easily found on Amazon*.
5. Squirrels
There is a love-hate relationship with birders and squirrels – perhaps more hate than love. Unfortunately, these rascally mammals pose a threat on our bluebirds as well.
Squirrels not only eat eggs and nestlings, but they have also been known to eat birds. When it comes to bluebirds, brooding or roosting birds are especially vulnerable to squirrel attacks. Squirrels are able reach into a nest box and catch nestlings or snatch an egg.
While it may seem like the nest box hole is too small for a squirrel to get into, they are able to gnaw away at the entrance hole, enlarging it so that they can crawl further into the box to snatch prey.
To protect your bluebird houses from squirrels, add a metal hole guard to the nest box to prevent squirrels from enlarging the hole. Additionally, a stovepipe baffle that is at least 8” x 24” will significantly reduce the potential of squirrels harming bluebird eggs, nestlings and adult birds.
6. Cats – Feral and Outdoor (Felis catus)
We love our kitties, but they are known for their hunting skills and have had a significant impact on native wildlife.
According to a peer reviewed paper published in Nature Communications, cats are estimated to kill 2.4 billion birds in the United States annually (median value). In Australia, the annual range varies greatly due to cat population and rain levels (Loss et al., 2013; Woinarsky et al., 2017).
This numbers presented in the Nature publication actually estimated cats being responsible for 1.3 – 4.0 billion birds annually in the US. This spread is a result of annual variation. The authors’ data also found a median annual value of 2.4 billion bird deaths resulting from cats.
Keep in mind, these numbers are an estimation and not hard numbers.
Cats are very much a part of our lives, and that will never go away. But these figures do show how important it is to keep cats indoor. Not only does it help native birds thrive, but also helps protect our beloved cats.
Outdoor and feral cats are less likely to eat eggs, but they have been known to do so. Mostly, they will go after nestlings and adult birds.
For our native cavity nesters who face a lot of threats, the hunting prowess of our cats is a little alarming because threats to adult birds, especially female, threatens the long-term populations.
To protect your bluebirds from cat predation, make sure your nest box is mounted to a metal pole not a wooden fence, tree or anything that is easily climbed. Use an 8” x 24” stovepipe baffle for better protection and consider a Noel guard to prevent cats from reaching into the nest box.
Keep in mind a Noel guard can deter your native birds. And they are not a good solution on their own. A wide, long stovepipe baffle is one of the best overall ways to protect your bluebirds from predators.
7. Falcons, Hawks and Owls (Falco, Buteo and Strigiformes)
Falcons, hawks and owls are excellent hunters, and can be predators of adult bluebirds and nestlings.
When it comes to the nest boxes, birds of prey can reach into the entry hole with their talons to snag a bird or nestling. Typically, in the air, hawks and falcons particularly won’t spend as much time on birds. Instead, they’ll focus more on small mammalian prey such as squirrels and chipmunks.
But that doesn’t completely rule out the chance. Bluebirders have reported hawks chasing after adult bluebirds in air, but in many cases, bluebirds were able to outmaneuver hawks in air.
Owls, are a little more cunning of the three. They are silent, exact flyers, easily able to capture prey in air.
Unfortunately, there aren’t a lot of ways to protect bluebirds during in-air attacks of birds of prey. However, you can install a Noel guard to reduce the threat of in-nest attacks. Or, use a birdhouse protector, which is a plastic extension that elongates the hole, making it difficult for talons to reach into the nest box.
8. Bears
Bears are a rarer predator of eastern bluebirds, but bear attacks on bluebird nest boxes have been known to happen. Bears will eat nestlings, and if able, brooding, and roosting birds. Because of their size, they are easily able to knock over nest boxes to get into them.
Bears are a difficult predator to protect your bluebirds from.
If you have bears in your area, the best ways to protect your birdhouses is to mount your nest box to a strong, reinforced metal pole. This will prevent bears from bending the poles. Additionally, use a birdhouse guard around the hole entrance. Rather than using a standard latch for the birdhouse opening, screw the access door shut. You can always use a screwdriver to open it up.
Again, bears are a rarer predator, but it is recommended to take extra steps if you have bears in your state or have seen them in your area.
Invasive Competition Species of Eastern Bluebirds
Predators aside, bluebirders will also need to protect their birds (whether bluebirds or other native bird species) from invasive competitors.
Invasive competitors of bluebirds include house sparrows, (English sparrows), Eurasian tree sparrows, and European starlings. These three birds are not protected by the migratory bird treaty act of 1918 (MBTA) and outcompete eastern bluebirds for their nest cavities.
Most specifically, the European starling and house sparrows are known to brutally kill eastern bluebirds and several other native cavity nesting birds in their nests. They will kill adults in their nests, nestlings, destroy eggs and build nests over existing nests.
The only sure way to protect eastern bluebirds from house sparrows and European starlings is by trapping and humanely dispatching. Nest traps like the Van Ert trap are one of the best ways to catch invasive birds. Deterrents can help but are usually ineffective in long-term situations.
Though the option of trapping and euthanizing may sound heartbreaking, a lot of bluebirders have invested a lot of time, only to discover the horror of what these invasive birds will do to bluebird families. Sadly, transformation from not being able to do this, to being able only comes after a nest box massacre.
If you’re trying to build up to this, one of the best ways is to simply Google pictures. That paired with being invested in your nest will help. As soon as you see a house sparrow or starling your guard will be up.
We do suggest having a Van Ert trap handy. Even if you don’t think you can trap and dispatch, your mind might change after a sudden attack. It is better to be prepared now.
Native Competition Species of Eastern Bluebirds
Native competition species are a difficult topic. Native birds are protected, and therefore, we as conservationists, and want-to-be landlords must allow our native cavity nesters to thrive.
In a sense, all native cavity nesting birds are competition species, however some competition impacts bluebirds in different degrees, with some birds not being able to easily compete against the bluebirds. With that in mind, we will provide a table of cavity nesting birds along with how they impact bluebirds.
Remember, do not interfere with native birds once they have begun nesting. It is not only illegal to remove nests or eggs of native birds, but it is also a human action that negatively impacts the natural balance.
| Cavity birds that use bluebird houses | Impact |
| Chickadee | Low impact. Protect chickadees.* Add a second box. |
| Tufted Titmouse | Low impact. Protect tufted titmice. Add a second box. |
| House Wren | High Impact – Will destroy nest and eggs. Use a wren guard. |
| Tree Swallow | Low impact. Add a second box. |
| Brown-Headed Cowbird | High Impact – Parasitic bird lays their egg in a bluebird box. |
For information on how to protect chickadees, which only have one brood per year, we have an excellent guide that explains what to do when you discover a nest, and how to make sure these sweet little birds thrive.
* Amazon listings are affiliate links. Purchases on Amazon using these links help support this website because we are given a small commission at no additional cost to you. Thank you for your support.
References
Grabarczyk, E. (2014, January). Vocal responses of adult Eastern Bluebirds (SIALIA Sialis) to potential nest predators and the behavioral responses of nestlings. Retrieved April 16, 2021, from https://encompass.eku.edu/cgi/viewcontent.cgi?article=1261&context=etd
