One of the most devastating things is looking inside your nest box and discovering the eggs your bluebird or chickadee or titmouse has laid is all poked. Just little poked holes that now render them inviable! This was the doing of a house wren, not to be confused with a Carolina wren.
The best way to prevent a house wren attack is to add a wren guard to your nest box as soon as the first egg is laid. This prevents possible nest abandonment by the parents since they are more invested in the nest, and prevents wrens discovering the nest hole. It’s very easy to make your own wren guard too.
A wren guard is a small barrier or hood-like structure that blocks the vision of a birdhouse entry hole. It is usually made of wood but can be made of plastic or even from cardboard. The hood-like feature of the wren guard blocks the view of the nest hole, preventing house wrens from seeing it or investing in the nest box.
When to put a wren guard on
The best time to put a wren guard on a nest box is after the residing bird had laid their first egg. This ensures the residing birds are invested and bonded to their nest and won’t abandon it. Don’t be surprised if it takes several minutes up to an hour for the bird to figure out how to get inside. But once they get in once, they’ll have no further issue.
If you can see your bird really struggling with the wren guard, it’s a good idea to adjust it if possible. If your wren guard is made of cardboard, this is as simple as trimming the cardboard.
If your wren guard is made of wood, you may be able to unscrew it from the nest box, and slide it back further, which will decrease how low the hood hangs over the opening.
When you do adjust your wren guard, you want to make sure that it doesn’t come too close to the actual nest hole, making it more difficult for your birds to enter. And you want to also make sure that the hood still blocks the view of the entry hole.
Something else we discovered helps tremendously, which we discovered by accident, is giving the birds a little bit of headroom.
Most of the time wren guards are mounted right to the roof of the nest box. However, in our DIY one pictured below, it’s tapped to a tick block of wood that sits on the roof. In doing so, it gave the birds a little more headroom to move around. This helped them get a little more comfortable with the wren guard.
How far down should the wren guard hood hang?
The key to placing your wren guard is to make sure it blocks the view of the nest box entry hole. Other important factors is making sure there is enough space between the hood part and the nest box, allowing the birds easy access. For bluebirds, that space should be about 4-4.5 inches minimum. For chickadees, 3-4 inches minimum can work.
Why is a wren guard so important
Wren guards are one of the best ways to discourage wrens from using an occupied birdhouse, and therefore preventing any attacks and loss of offspring.
House wrens are known for going into occupied nest boxes, poking the eggs and throwing them from the nest. They have killed nestlings and thrown them out of the nest, and have built their nests over nestlings.
While a bluebird is much larger than a house wren and is a wonderful nest defender, bluebirds often leave their nests to forage for food. And this even happens during egg incubation as continuous incubation (nonstop sitting on the eggs) does not actually occur and would be detrimental to embryos.
During the parent birds’ absence, a house wren will go in and do its damage.
The wren guard blocks the view of the nest hole and can therefore prevent house wren attacks. However, these are not a 100% protector. There will be times when a wren guard will not work.
When a wren guard won’t work (doesn’t mean you don’t try it)
If a wren has already gotten into the nest box, this will reduce the effectiveness of a wren guard because the house wren knows the entry hole exists and where it is. This doesn’t mean you shouldn’t try. A wren guard still has the potential to save you. It just lowers the chance of it being effective.
Just because the house wren has gotten into the nest, they may not necessarily be bonded to it. This will also help the chances of your wren guard being effective.
Your best hope, if you know or suspect a wren is in your area and has even hurt some eggs is to still put up the wren guard and hold out hope that the nestlings grow old enough to where the house wren becomes less of a threat.
When to take a wren guard off
Take the wren guard off once bluebird nestlings are about 8-10 days old. For smaller nestlings like chickadees and titmice, wait until nestlings are about two weeks old before guard removal. However, if nests are being harassed by other birds, leave the wren guard on until they are old enough to fledge.
Taking the wren guard off at this point is important to allow the baby birds to properly fledge the nest. One source also suggested that delaying wren guard removal may cause feeding issues, which is reason to take it off once they’re older. But again, if there are threats from other birds, it might be safer to leave it on until they are fledge ready.
At this point the nestlings will be big enough that a house wren won’t be able to throw them out of the nest or build their nest on top of them.
House wren vs. Carolina Wren
Color is one of the biggest differentiators between a house wren and Carolina wren. House wrens will be a dull, gray-brown color. Carolina wrens, on the other hand will be a vivid chestnut brown with a yellowish breast.
The breast of a house wren will also be a little more spotted, and they are ultimately a little smaller than the Carolina wren.
It’s very important to point out these differences because the Carolina wren are not a threat to cavity nesting birds. Usually, they will not nest in cavities. Instead, they’ll nest in just odd, random places. But when they do seek out a nest cavity, they will not threaten or harm your nestlings if the box is already occupied.
Carolina wrens are very curious, and very loud, impressive singers. They’re great little birds to watch.
And that’s not to vilify the house wren. House wrens are native species who often leave a bad impression. But it’s also important to remember that they play a contributing role in the native ecosystem. As conservationists and bird lovers at heart, we must keep that top of mind when considering a house wren.
It’s ok to discourage house wrens, but it is not ok to interfere with them once they have laid eggs. It is ok, however, to remove dummy nests – because house wrens will sometimes build dummy nests.
