(Originally posted by Bet from CT on bluebirdnutcafe.yuku.com)
Very clever! I think bluebirders can be so innovative!
I would DEFINITELY not install this BEFORE an egg was laid if you can help it. I don’t think it needs to be quite as long as the picture shows. It just
needs to hide the hole from a passing House Wren (HOWR).
I know some folks had experimented with a more U shaped (squared off) wren guard with sides on it. I don’t know if they ever wrote up whether it worked
as well/better, or how readily it was accepted. Would be very interested to see what happens if you test this.
Supposedly it is best to have the wren guard made of the same or a similar material to have it blend in with the box.
Blaine’s design is useful in that it can be used on a FRONT opening box (the guard bends up when you open the door for monitoring.)
Also, remember to take it off when babies are too big to be carried off by HOWR (for bluebirds, this is about day 5.) It does make it harder for the parents
to feed. But it’s better than having the eggs/babies thrown onto the ground!
The following was posted by Bet on the Cornell List on 6-12-09
I’ve updated my webpage on deterring House Wrens ([url]http://www.sialis.org/wrens.htm%29[/url]
with the following warning about wren guards (a view blocker that
extends from the front edge of the roof to just below the entrance hole
– see drawings and photos – [url]http://www.sialis.org/wrens.htm#drawing%29.[/url] I’m NOT saying they shouldn’t be used – just that
they should be used CAREFULLY.
TIMING: Watch the box after installation to verify that the nester is
able to enter. DO NOT PUT A WREN GUARD UP AFTER EGG LAYING IS OVER
unless you VERIFY that the parents will enter the box, especially with
other species like Tree Swallows! If the parents refuse to go inside to
incubate, brood or feed, the eggs or babies WILL ALL DIE! Putting up a
wren guard before egg laying begins may result in nest abandonment with
some species (e.g., chickadees, titmice.)
Here’s some background.
Wren guards were “invented” by Orthwein, and I’ve used them
successfully on a number of Eastern Bluebird nests to deter House Wren
attacks. (House Wren populations are increasing in my area, and so are
attacks, in some cases farther and farther from “typical” House Wren
This year, I tried putting one up in a park on a
chickadee nest BEFORE egg laying began, and the nest was abandoned.
(I’ve put them on chickadee boxes during egg laying and all were
I tried one on a titmouse nest during nest building
(in a box with a nestcam on it) and the titmouse would not go inside. I
removed it a day later and she went in and finished the nest and laid
eggs, which a House Wren then destroyed when they were close to
hatching. I put one on another titmouse box during egg laying and it
I just got a very sad report from someone who put up a
guard on a Tree Swallow box as the eggs were hatching. It was properly
installed, even farther than 2.5″ away from the hole, but the parents
refused to enter. The landlord went back the next day to check on the
box, and all the babies were dead.
Also, I’m NOT convinced that repeated removal of House
Wren nests (especially if they are not dummy nests – removal of nests
with nest cups or eggs is not legal under the Migratory Bird Treaty
Act) doesn’t increase aggression (similar to experiences some trail
monitors have had with repeated removal of House Sparrow nests and eggs
– a discussion I am NOT suggesting we engage in again right now.) Some
people have had good luck with moving boxes 300 feet or more away from
brush/forest edge. I’m guessing increasing forest fragmentation (from
development) is creating more opportunities for House Wrens.
Anyway, I would be interested in any reports from
others regarding success OR failure with wren guards, especially with
regard to other species of cavity nesters. I will update
recommendations on my website accordingly.
Bet from CT
- This reply was modified 7 years, 4 months ago by The Original Bluebird Nut.