2 hole birdhouse

I spent two enlightening years corresponding with Linda Violett discussing the theory behind the 2-hole nestbox, and how it does succeed in reducing attacks from House Sparrows. As Tammy said, the main attribute of two holes is to provide a Bluebird with another way out of Dodge if a HOSP has stuffed itself into one entry.

Inside a nestbox, the House Sparrow will invariably defeat the Bluebird. If a Blue can take the fight outside however, its superior flying skills heavily tilt the odds against the sparrow. We’ve seen or heard of this when sparrows are foolish enough to attempt a box takeover when the adult Bluebirds are outside and nearby. I honestly don’t know if a Bluebird leaving the box to fight outside is pure instinct or a learned behavior. With 2 holes, they have a better opportunity.

For the longest time, 2-holers were an almost exclusive west coast thing, and most are hung in trees out there (2-legged predators warrant this hanging approach; I use this method myself at public parks). In 2016, I built as many 2-holers as I did Gilwoods, all of which were shipped east of the big river. I don’t think any of these were hung in trees. Seems the popularity of the 2-holer is growing, albeit slowly.

You don’t have to build or buy a Violett 2-Hole Mansion to get the dual entry. A lot of nestboxes can handle 2 entry holes as long as the front is at least 5 1/2″ wide, which covers a lot of box designs (Nabs style boxes and the new XBox for examples).

Last year I tried normal sized boxes with an extra hole in the side and still had a bluebird killed. They succeeded in a similar box on the same property. This year I made a bigger box. I think the size matters so that a bluebird can fully extend its wings inside. Less chance of getting trapped.