House sparrows yard life

[Frank Kolwicz]

I've had nest boxes designed for Bluebirds in my yard for almost 20 years and House Sparrows have been around in small numbers all that time and never got in. Until, starting last year the HOSPs have taken over or attempted to take over the three that have been there for 5 years or so. Prior to last year they were not able to enter and Tree Swallows used the box, as they have used the others all along. Last year the HOSPs got in, even through the armored opening (covered with a metal outlet cover) and, of course the one unarmored box that woodpeckers enlarged.

Over last winter I partially blocked one of the armored holes with a thin strip of wood that covered the top 1/4" of the hole, making it even smaller vertically, but the same horizontally, and they got in there, too.

I finally blocked the opening again with an additional strip of wood 1/8" thick added to the previous one. HOSPs have not gotten in that one, so I'll have to make that change to the second armored box and get rid of the one that's been routed-out.

That's a long lead in to this question: are HOSPs getting smaller to allow access to smaller hole boxes?

I have yet to see other, smaller, species using the blocked box, but that's because the HOSPs are mobbing that one and Chickadees, etc. have had no chance on using it.

Thanks for any info,

Frank
In Monmouth

[Lisa Millbank]

Hi Frank,

Here's a good resource about House Sparrow controls, including sparrow spookers, hole reducers and lots of other information: http://www.sialis.org/hosp.htm.  House Sparrows enter standard bluebird box holes easily, which should be 1-1/2" to 1-9/16" in diameter (some sources say 1-9/16" is preferable for Western Bluebirds, but no larger, to keep out European Starlings).  House Sparrows can enter holes that are quite a bit smaller than standard bluebird box holes, but not 1-1/8", the size of chickadee/wren box holes.  It's important to use some other method of House Sparrow control for boxes with holes larger than that.  Unfortunately, restricting the hole size of standard bluebird or swallow boxes will probably make the boxes unsuitable for those species.  Sparrow spookers are widely used and I can't recommend them enough; they make a huge difference.

Some smaller female House Sparrows can enter horizontal slot-style boxes designed for Violet-green Swallows (7/8" high x 1-1/2" wide), but it's difficult for them, and they nearly always give up.  We always use a sparrow spooker to stop House Sparrows from harassing the swallows.

Different pairs of bluebirds and swallows may be better or worse at defending their boxes.  Really vigilant pairs may give House Sparrows enough beatings that they never do get into the box, but more passive pairs will lose clutches or even their lives if they get caught inside the box with a House Sparrow.  They really can do a lot of damage to native cavity nesters, so it's a good idea to use multiple proven methods to protect your nest boxes.

I don't know if House Sparrows are actually getting smaller, but I think there have always been outliers that can fit into "sparrow-proof" holes, and the majority of nest boxes are easy for them to enter anyway.  I'm doubtful that there's a really significant advantage to being smaller, at least not enough to change the population. 

Lisa Millbank

Here is an excerpt about hole sizes from Sialis.org:

ROUND
1 1/4" diameter allows HOSP entry.
1 1/8" diameter stops entry. (NOTE: Keith Kridler of TX has had HOSP nest in boxes with an exact 1 3/16" hole. Phil Berry of FL reported HOSP entering via a 7/8" restrictor used on a box with Brown Headed Nuthatches nesting.)
HORIZONTAL SLOT
1 1/2" x 1" slot allows entry.
1 1/2" x 7/8" stops entry.
VERTICAL SLOT
1" x 1 1/2" slot allows entry.
7/8" x 1 1/2" slot stops entry

Note: Mike Donahue of Seattle had a HOSP build a nest in a Violet-green Swallow box with this slot size.

DIAMOND or SIDEWAYS OVAL HOLE

Malcolm Rodin has experimented with sideways oval holes for Violet-green Swallow boxes which he found deters adult HOSP if it is NO TALLER than 7/8". He makes the hole using a 7/8" and a 5/8" Forstner wood bit. Drill three hole, using he 7/8" bit for the center hole, and the 5/8" bit for the holes on either side. Then file and sand to get a good oval shape, but do not exceed 7/8" in height. The width will be between 1.5 to 1.75" inches. See video on how to make.
Gene Derig of Washington makes a wide diamond hold and has found it deters HOSP but allows Violet-green Swallow and chickadees to nest. The diamond he uses is 3.00" wide, and the height is EXACTLY 7/8" (this measurement is crucial.) The cut is straight lines all the way from peak to corner, and you can make it with just a chisel and a hammer. Derig does not use wood thicker than 3/4", and files down the inside of the entryway to make it easier on the swallows.

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