Violett's 2-Holed Bluebird Nest Boxes . . .  

When 2-holed boxes are placed at House Sparrow problem areas, adult bluebirds are able to survive an attack by escaping out the second hole and taking the battle outside the box where bluebirds are able to outcompete House Sparrows.  The three most important links are

Why monitors using 2-holed boxes (per Keys) do not have to trap.  And why trappers continue to use 1-holed boxes.


Box Depth (deeper boxes protect nests from avian predation)

Floor Size Visuals (don't build/purchase tiny boxes

Design Your Own Box  (it is easy to design a box to suit)

Other Box Plans  (huge list of boxes, each similar to the next;  this 2-holed box, for example, is only a large version of a standard box but with another hole)

Large Slot Box (alternative to building a 2-holer)

Hangers (you don't have to put a box on a post)

How to Grow Mealworms (step-by-step instructions & photos)

How to Feed Bluebirds (putting out mealworms, etc.)

Southern California Bluebird Club (Home page of club that is hosting the 2012 NABS conference)

Tree Swallow Project   (Chris Gates is one of the few who speaks clearly about nestbox sizes) 

Sparrow Spookers / Magic Halo  (emergency fixes for 1-holed boxes under attack)

San Diego Bluebird Club   (All the basic info for new bluebirders)



I've been using 2-holed boxes successfully on a large urban (city) trail for over a decade and, over time, have identified simple Keys to Success .  Please refer to test site logs (links below) as to what you can expect during a transition from problem 1-holers to defensible 2-holers.


Note:  I am a grassroots monitor and do not sell nestboxes.  There is no personal gain (directly or indirectly) in sharing this information. 



Emergency Add-ons for post-mounted 1-Holers:

If you are in the middle of an emergency and need bluebird protection from House Sparrows for an active post-mounted 1-holed box (and no time to build a 2-holer) consider purchasing  House Sparrow Spookers or a Magic Halo  (available from bird supply stores such as  Wild Birds Unlimited, Yorba Linda.  You must also remove any feeders and extra boxes that are attracting House Sparrows.

Anyone who lives near Yorba Linda, California, may contact me,  Linda Violett, and I will loan you a 2-holer to get you through the crisis. 


Defensible Nest Box:  Two-holed boxes are not technically House Sparrow resistant.  They are well-made nestboxes that Bluebirds can defend against House Sparrows.  The success of the design is based on Bluebirds escaping from a box under attack and outcompeting House Sparrows by taking the battle outside the box where bluebirds have the advantage over House Sparrows.  That goes hand-in-hand with removing feeders and extra boxes.

See some great photos of Bluebird Battles taken by Dave Kinneer of Virginia.

Here is a link to help identify  HOSP Eggs.   However, the photos of the trashy nests (which are indicative of House Sparrow nests in Eastern Bluebird areas) look very much like the trashy nests Western Bluebirds often build in urban  (trashy) parks here in southern California. 


Even in city areas that were labeled by other veteran monitors (Dick Purvis and Bob Franz) as "unsuitable because of House Sparrow Problems" have now been re-opened by using 2-holers and proper spacing (adequate forage for each nestbox).  Eisenhower Park (Orange, California) is a classic example.



Two-Holed Performance Tests


Mixed Test Sites below (mix of box styles, site conditions and techniques at other no-trap sites) 




Anyone who traps or shoots non-native birds, should first learn the difference between House Sparrows and Killing House Finches(Finches have streaks in their breast feathers as shown on the dead birds in this video.)

Here is a video of the: Non-native House Sparrow and Starlings



Is Trapping Actually Effective?

Bet Zimmerman (author of is an expert House Sparrow trapper.  Concurrently with the no-trap site (link above), she set up a trapping site at Taylor Brooke Winery using a 9-box mix of 1-holers and HOSP-resistant boxes.  Bet's trapping site had non-stop House Sparrow problems during the 3-year period.  Very few bluebirds fledged.

This trapping site was set up and monitored by one of the foremost authorities on trapping and controlling House Sparrows: See Bet Zimmerman's extensive information at:  Managing House Sparrows and Managing House Sparrows Experimental

  • Very few bluebirds fledged during the intensive 3-year trapping program.

  • NO bluebirds fledged from any of the standard 1-holed boxes during the 3-year trapping program.

  • Only boxes that offered an opportunity for bluebirds to escape (slots or wider-than-normal holes) were successful in fledging bluebirds.

From these results, it appears that the potential for bluebirds to escape out of a box under attack is of greater importance than trapping.

  • Links to Bet's logs are provided below.

2008 trapper's logs     27 HOSP trapped; only the SLOT box fledges bluebirds

2009 trapper's logs   7 HOSP trapped, no bluebirds fledged

2010 trapper's logs    5 HOSP trapped, only one clutch of bluebirds fledged from a Gilwood Plans (semi-slot box with a 2.25" wide mouse hole opening) and Spooker attached.   Photo shows Gilwood box style.

For those who rely on trapping House Sparrows, the job never ends and results are sporadic.




Note to homeowners who feed house sparrows: 

Here is a link showing what some Bluebird monitors have to go through to catch House Sparrows:  Trapping   In our southern California urban area, most monitors using 1-holers will remove boxes from HOSP-infested areas.   House Sparrow problems are usually a result of homeowners feeding and raising House Sparrows.

If you feel you must feed birds, be selective.  Limit your offerings to Hummingbirds/nectar; Safflower (not sunflower) for Finches/Doves; thistle for Finches/Siskins. 


* Trail management is just as important as nestbox design.   Sparrows are not allowed to use nestboxes on this trail and they are never allowed to sit on eggs or young.  Bluebirds need two acres forage to find insects. Boxes should be spaced at least 300 feet apart for consistent results.


If House Sparrows actually avoid a nestbox style, there is a reason.  Before purchasing any so-called "House Sparrow Resistant" box, you should ask why the box is not acceptable to House Sparrows.  Usually, it is because the box is too small.

See Floor Size Visuals



Mountain Chickadees

Wood Ducks


Since June 15, 2012   


If you came to this site with a specific Bluebird-related question that is not answered, please contact me, Linda Violett