How to Protect Tree-Mounted Nest Boxes from Snakes
June 29, 2021By Holly Grant, NestWatch Project Assistant
A Wily Predator
This nest box's predator guard was circumvented by a Western Ratsnake.
One of the best ways to prevent predators from accessing your nest boxes is to mount your box on a pole. This placement can make it easier to add predator guards, such as baffles, which have been shown to prevent climbing animals from accessing nests. Climbing nest predators in North America range from mice, to squirrels and raccoons, to cats and even chipmunks, but perhaps none draws as much public ire as snakes.
While adding baffles to your nest box poles is one of the greatest defenses against snakes, sometimes mounting boxes on a pole is simply not feasible. How do you protect a tree-mounted box, or those mounted on other wider structures, such as utility poles? New research points to a helpful new predator guard design.
In Defense of Snakes
Snakes are an often underappreciated group of animals. There are more than 3,000 species in the world; in North America, we have around 130 species. These reptiles mainly eat small mammals, birds, eggs, frogs, insects and other arthropods, so it comes as no surprise that snakes are a common nest predator for birds. For this reason alone, many people dislike them, but snakes are an important part of the ecosystem and can even be helpful to birds. How? While we may not want them depredating our nest boxes, having snakes nearby can act as a natural control and reduce the abundance of other nest predators, such as mice, chipmunks, small mammals, and even other snakes.
Having snakes nearby can be generally helpful, but it’s still a good idea to protect your nest boxes from predation. Some nest monitors have tried methods which trap the snake, but this can be potentially harmful to you (e.g., if you must handle the snake to release it) or the snake (e.g., if you do not find it in time). Snakes are also often legally protected wildlife (like birds) and trapping them should only be done in accordance with your local regulations.
A New Snake Guard
New research shows adding plastic sheeting (acetate) around a tree trunk can help prevent snakes from reaching nest boxes. Click to enlarge photo.
A new guard for trees
A recent study published in Animal Biodiversity and Conservation discusses a simple new predator guard designed to prevent snakes from reaching tree-mounted boxes. Researchers in Spain tested the efficacy of an acetate sheet (transparent sheet of flexible plastic), that was 80 cm (31.5 in) tall and 1 mm (0.04 in) thick, by wrapping the sheeting around trees beneath mounted nest boxes. The researchers first cleared branches and bushes in a 1-m radius around each tree, and then waited until the host species (Great or Blue Tits) had begun laying eggs. They then added this acetate sheet to the trunk and affixed the sheets to the bark with duct tape. Forty randomly selected nest boxes were protected by this acetate guard, while the remaining 74 occupied boxes in their study were left unguarded as controls. The researchers used nest cameras to verify predator identities.
It’s a wrap
They observed a clear difference: the plastic sheet guards were significantly effective at preventing snakes from depredating the birds’ nests. The authors found that 20% of the control boxes were depredated (15 incidents), while only 2% of boxes protected by the plastic sheets were depredated (1 incident). In the one case where there was a successful predation event on a protected box, the authors suspect that the snake may have used a nearby tree to jump to the nest box, avoiding the plastic altogether. The authors were able to record a snake exhibiting this behavior elsewhere in the study area, to confirm that it was indeed a possible explanation.
How to Do It:
- Acetate sheets can help prevent snakes from accessing tree-mounted nest boxes. Use a sheet that is about 32 inches tall, and a width that will allow the sheet to wrap entirely around the trunk. Use duct tape along the top to secure the guard to the tree.
- If you have a tree-mounted box that is close to other trees or branches which a predator could use as a jumping-off point, add another acetate predator guard on those nearby trees. Be mindful of how the upper branches come into contact with other trees and vegetation as well.
- This guard can be used in combination with a Noel guard or entrance hole extender block to further restrict the entrance from birds, mammals, and other would-be predators.
The researchers also noted that snakes have long-term spatial memory, and so nest predation by snakes may increase over time in any given area once boxes have been discovered. Understanding the behavior of predators and how they fit into the ecosystem can help everyone live more harmoniously. We encourage NestWatchers to try this new method out, especially if you are looking to find a new way to prevent snakes from reaching your tree-mounted boxes, or those mounted on utility poles. Despite the improved nesting success documented with predator guards, it’s good to keep in mind that no predator guard is ever 100% effective, and it’s best to have realistic expectations that you cannot prevent all predators from getting at nests.
Reference:
- Navalpotro, H., D. Mazzoni, and J. C. Senar. 2021. A plastic device fixed around trees can deter snakes from predating bird nest boxes. Animal Biodiversity and Conservation 44(1):103–108. https://doi.org/10.32800/abc.2021.44.0103
39 comments on “How to Protect Tree-Mounted Nest Boxes from Snakes”
Thanks for this tip. We once watched a bull snake slither into a western bluebird box mounted on a ponderosa pine while the parents flapped about futiley
This is great. I am wondering about how exactly the duct tape should be applied. I wish there had been more detail in regard to that. I wouldn’t want to harm my trees by causing the bark to get ill. I am wondering too if this wouldn’t work for preventing caterpillars from climbing trees?
My guess is that it’s not applied directly to the tree, but the acetate wrapped as a tube around the tree and duct taped at the acetate seamline
In the 1950s, maybe even early sixties, trees in Ohio were similarly covered in burlap. Can’t remember; suggest purpose was to protect against caterpillars, possibly spores.
This was from the Ford Foundation? A Time to Choose? You could probably find a record at Wooster; it was Ohio board of Forestry work.
Hi Maureen, In the study, the plastic was wrapped around the tree trunk and taped along the top edge to the trunk. It didn’t mention whether the long edge was taped as well. It’s possible that there could be some moisture buildup under the tape, which can case rot/insect infestation (ants). There’s a product called tree wrap which has ventilation holes to prevent this, but it isn’t generally adhesive. Temporary tape might be ok, but it could peel young bark or trees with thin bark. It may be a good idea to apply the predator guard only while the box has an active nest, to give the tree room to breathe and grow.
Thanks for the idea for preserving nest boxes, or natural tree cavities for that matter, from snakes. I am not on favor of using plastic of any kind so I’m looking for an alternative, how about recycling something already in our possession? My first thought is the heavy non-recyclable plastic bags from large dry dog food in place of the acetate sheeting. I think if the bags are washed then used with the slippery inner side facing outward it could be just as effective and give another life to an otherwise very wasteful throwaway material.
Hi Barbara, This study only looked at acetate sheeting so we can’t speak to the effectiveness of other materials, but I like your idea of recycling this way! Whichever material you use instead, it would be important to have a smooth surface on the outside and one that is taut – any wrinkles or bunching would provide a way for snakes to gain purchase on the material. Acetate sheeting is firmer than most plastic bags which gives it this advantage. Alternatively, you can mount your boxes on poles relatively inexpensively. Here’s some information on how to do so.
15 – 18kg birdseed bags, such as the type that black oil sunflower seeds come in, should work. The bags are strong and durable. Just cut down the seam to open them up into one piece, and then wrap around the tree.
I have use these to keep raccoons from climbing the trees to reach birdfeeders.
I use carpet tack strips on poles and 4×4’s.
I cut to fit and secure with duct tape or wire.
IThe snakes have not won in years.
Thanks for a great idea!
We tried the tack strip using full four foot lengths. Squirrels and snakes went right up it! Our rat snakes are tough skinned creatures hahaha
Around our area of mid Michigan I’ve never had snakes in any of my boxes. I have 3dozen bluebird boxes around 140 acres of fields. All used to be filled with tree swallows, bluebirds, and some barn swallows. I used the love watching them fly around the tractor as I was cutting hay, feeding on the insects flushed out by the hay bind. The year after the authorities sprayed for the Zika mesquito the birds never returned. I am lucky to see one pair of each species. I suspect with the bugs gone, the birds are gone without proper feed.
Just sad to lose that basic level of food chain… and see what happens.
I’m wondering the same. Duct tape probably adheres ok to smooth-barked trees and utility poles, but a chunky-barked tree might be a challenge. It certainly won’t be attractive, though duct tape does come in a range of colors besides sheet metal gray. Butternut Brown, perhaps? Also, how does duct tape hold up in wet weather?
This might also prevent small critters like squirrels and chipmunks from climbing a tree they need to climb, e.g., which has their nest in it. Has that possibility been addressed?
Hi Cheryl, Good question! This design only looked at prevention of predation on nest boxes. That said, squirrels and chipmunks can typically access much thinner and higher branches than snakes, and therefore can travel among treetops a bit easier. Regardless, it’s a good idea to install this guard only when there is an active nest, and to take it down once the young fledge. Alternatively, you can stick to mounting nest boxes on poles. Check out this FAQ for more info on installing a thin nest box pole.
In hot climates, like California, did they look at whether the plastic harmed the bark, and the tree? It seems considerable heat could build up underneath the plastic.
Also, this guard should be removed when birds aren’t nesting, to prevent girdling the tree.
Hi Greta, we agree, this guard should only be applied when the birds have an active nest, in order to prevent harm to the tree. The study was done in Spain, but they did not look at the effects of the plastic on the tree itself. Short term use should help reduce potential side effects.
Very interesting. Would help if you specified the type of sheeting and where it can be purchased. Also, will this also deter raccoons?
Hi Rich, This study used 1mm thick acetate sheeting (flexible plastic). You can find flexible acetate sheets from many online retailers, like Amazon, and some hardware stores.
I have a nest box question.
How do you attach a nest box to a tree without putting nails, screws, bolts, etc. into the tree itself?
Hi Marty, Some monitors opt to use an adjustable metal band that can be secured around the trunk (belt-style), which the box is attached to. In this case, it would be important to consider loosening the band as the tree grows to prevent damage to the trunk.
You can also use large (30 inches or selected other length) cable ties available at your local hardware or home improvement stores.
Wrap one each above and below your bird house tightly against the tree and then cut off the excess.
What is the thickness of the acetate sheet, and where would one buy it?
Hi Frank, the acetate sheets in this study were about 1mm thick. You can find flexible acetate sheets from many online retailers, like Amazon, and some hardware stores.
I had no luck finding acetate sheets 1 mm thick and 32 inches long- only shorter 12 inch sheets were listed. Any other suggestions on where to purchase this item?
Also, is the lower edge of the acetate left “flapping in the breeze” or is taped to the tree also?
Hi Penny, If you search for “acetate roll” on the internet, you should find several options, including from art stores and some industrial stores. And yes, the bottom is not taped to the tree; you may also want to overlap the acetate around the tree at least several inches.
So there is something living in my bird house on a pole. I will not see it for days and then it will stare at me for hours. I can’t get close enough to see what it is. And I never see it coming or going, just the head. This has been going on for weeks.I work remotely and he is just out the window.
Could it be a flying squirrel? They are nocturnal and do occasionally inhabit bird houses. We had one in our birdhouse and so has a friend in the area.
I used chicken wire about 18 inches in length wrapped several times around the post/tree and cut many of the sides of it once wrapped so they stuck out like spikes. I attached it with twisties. So far so good and also keeps squirrels away as well !
Intresting, I have stayed away from tree or even wooden fence posts nrst box mounting just for the easy access preditors have. Even using pipes for poles is no gurarntee. In heavey snake areas I use stove pipe baffels to discorage preditors. This looks looks like it might be a good alternative to look into. Thank you
I wish you could post a picture of what you’re talking about. It sounds like it would be extremely useful. I would just like to see it before I start to try to replicate it.
where do you buy 32″ sheets
Hi Terri, You can find flexible acetate sheets from many online retailers, like Amazon, and some hardware stores.
My bluebird boxes are on fence posts with fencing hooked. How does this work for me??
Hi Carolyn, We’re not aware of any predator guards that would prevent climbing predators from accessing fence-mounted boxes. Cone and stovepipe baffles work best for deterring climbing predators like snakes on thin poles, and the design discussed above works for thicker poles and tree trunks, but fences generally provide lateral access to the box which can be hard to prevent. You can try adding entrance hole-extender blocks or Noel guards to help guard against predators that might reach into the box (but which can’t fit their whole bodies), but if you want to prevent snakes specifically, we recommend re-mounting your box on a pole or tree so that you can apply the appropriate predator guard. Here’s an FAQ with instructions on how to install a pole in your yard relatively inexpensively.
I commend you for what you do to encourage individuals to help cavity nesting birds, but I take issue with your instructional .pdf at your FAQ you link to which states that a predator guard is “optional….” If we lure birds by placing boxes, we, as landlord s who lure, are 100% responsible for blocking climbing predators with a proven method. The cone you utilize does not block the constricting rat snake, nor does it block a raccoon. Most wild bird store owners would instruct you not to use that guard against snakes and raccoons. For five years, on now over 200 poles, I have blocked climbing predators 100% of the time by essentially the same theory used on the tree in your article. I know this without even being there to witness the attempts through use of a lithium line detector on the 5-foot HVAC duct. We must first do no harm. Predator guards are not optional and only proven methods should be used. It may be a hobby for us, it’s life and death for the birds.
Hi Marcia, We strongly recommend using predator guards on nest boxes, but it’s true that they are optional, because birds will be attracted to nest boxes without predator guards. Every predator situation is different, and some guards work in some areas where they might not in others. No box can be made 100% predator-proof, but the tips on our webpages are certainly great places to start. We’re glad to hear you’ve found a solution that works for your nest boxes.
Holly, I’m not sure I understand your statement that birds will be attracted to boxes without guards so guards are therefore optional. (“…they are optional, because birds will be attracted to nest boxes without predator guards.”) Also, certainly some guards may work in some areas where they might not, only because the predator species doesn’t exist there, but that doesn’t mean the guards will work in some areas and not others due to the fact that raccoons or snakes will alter their climbing methods. They will climb the same way no matter the habitat. Saying “no box can be made 100% predator-proof” is not what I have found so far with respect to the two main climbing predators. And, my boxes are located in suburban back yards, golf courses, and farms, i.e. different habitats. The predator guard you show in your video and in your .pdf does not guard against raccoons or snakes even though you call it a “predator guard.” Photos and videos show they don’t stop raccoons and snakes. Finally, to not place a guard on a pole is actually unnatural. A bird nesting in a cavity high in a tree is naturally guarded because it is harder to see and hear the nestlings and the feeding activity. To mimic the safety of that at a lower height in a box, we have to guard the box. Not using one boosts the risk of predation over a natural cavity, because the box is easier to spot by a climbing predator. It’s best practice to try to duplicate the natural living conditions, so not guarding a pole placed a level made easy for us, yet risky for them, in my opinion and through my experience, can harm.
We have a barn swallow pair that nests above our front door every spring/summer. A few nights ago our camera caught a rat snake climbing up and taking one of the baby birds. I know of no way to keep a snake from climbing up the side of a door – does anyone else?
Did you ever solve this? We have swallows nesting on porch columns for years as do many neighbors and friends. Do acetate sheets really work? Should we tape them to our porch areas?
Will this stop raccoons as well?
Hi John, This study was focused on preventing snakes, but the smooth plastic sheeting would likely be hard for most climbing predators to get a grip on. I’d recommend mounting it on a tree that is not too close to other trees where the raccoon could jump across using the upper branches (and therefore access your nest box from above).
I love reading these articles they teach me a lot ! I will keep the acetate sheeting in mind but I have had great success mounting my boxes on conduit poles and heavily greasing them also stops red ants which can also be a huge problem in a lot of boxes.
We watched a cardinal’s nest with blue eggs in my rose bushes. We installed a
low wire fence around the
bush, but the eggs soon vanished. We have a couple rat
snakes in the area and we believe they got the eggs. However, crows also empty nests
of eggs and young. The crows come hunting in twos. We had a nest in a high hanging
moroccan lamp in our entry. It remains empty. Predators have to be hastening the extinction of birds. Our wonderful mocking birds sang for us for years before hawks ate them. The males perch on the highest treetops. They have vanished.
I have found after years of trying different methods. I finally decided to give mending plates a try. You’ve seen them holding trusses together they are very sharp on one side. Use gloves and pliers to bend one around the pole your bird house is secured to the pointy side out. I’ve just started doing this but several different birds have taken residence even the tree sparrows are back. Still waiting on the return of our beloved Eastern Bluebirds
Thank you so much for this suggestion. I’m going to try this the next time the house finches and kingbirds have baby birds up in my carport.
I cannot find 0.04″ thick rolls of acetate on Amazon or anywhere else. At most the rolls are 1/10 that thickness and at most 25″ wide. If you have found it please supply the link. Sheets of other plastics that thick are available but very expensive.
I’d love to see a response to this as well.
Thank you.
Slightly different problem. We have a robin’s nest in the crook of a gutter downspout, 25′ up a brick wall. A rat snake climbed between the downspout and wall to predate the nest. I think the acetate would have to be wrapped around the downspout and spread across some portion of the brickwork, to be effective?
Not all nests can feasibly be protected from climbing predators. This sounds like one which would be impractical to try to guard, and doing so might create too much disturbance.
Curious if a shiny or reflective type of plastic or Mylar would work? I’m thinking of a horticultural highly reflective mylar film that comes on a roll. Are snakes deterred by reflective surfaces, and would the shiny reflective surface do a double duty? Or what about reflective insulation sheets?
Does this prevent squirrels too?
I live in the tropical rainforest and we have an abundance of snake predators. Has anyone tried razor wire as a deterrent? Many small birds here build their nests in our citrus trees to take advantage of the natural sharp spines. I’ve watched snakes easily climb the palms, smooth PVC pipes, etc. Any help appreciated.