QUICK TIP: Monofilament (fishing line) on a bluebird nestbox is initially somewhat effective during the breeding season as a preventative measure to keep House Sparrows (HOSP) from claiming the box. They may ignore it once they become accustomed to it (e.g., during roosting season.) Once a male has bonded to a box, he will not abandon it unless the box is taken down or the hole is plugged.
“… Although lines did not repel House Sparrows from nest boxes, they apparently cause an initial delay in use of newly erected boxes. Further study might develop this result as a method to help other cavity nesters initiate and more successfully defend nests from House Sparrows….” (Pochop, 1993)
Several people have experimented with using monofilament on nestboxes to scare off House Sparrows. their work is summarized below: Frank Navratil Sr | Larry Zapotocky | Mike Ripple
Navratil tried using monofilament (fishing lines) on nestboxes in 1999, and said: “In general, the sparrows were deterred from birdhouses until June. Then like a dam breaking, the sparrows seemed to ignore the monofilament at many birdhouses. Yet at other birdhouses (even where they had nested previously) they remained deterred. Adding monofilament to a birdhouse already occupied by sparrows is simply ignored by them.”
Later on, he replaced wood houses with PVC buoys, painted them white, and changed the entry to vertical ovals. In the early spring of 1999, I hung monofilament on the houses. (Four simultaneous changes.) None of the boxes were used by House Sparrows, one was used by Tree Swallows. This could be a response to “neophobia” (fear of new things.
Zapotocky indicated that HOSP eventually figured out how to get in to Ripple’s design. He added monofilament to the roof of the box, but again they hesitated for a while and then got in…. I decided to devise a way to place the mono on the nestbox that looks very confusing and distracting. In the beginning I was nervous because I wasn’t sure if the Bluebirds would accept it…. So far the Bluebirds have had no problem adapting to it. They initially were very curious to what it was. They did bump into it a few times, but once they figured out how to negotiate it, they flew right in (which took all of 10-15 minutes). In no time the Bluebirds were flying in and out like it wasn’t even there. At this point, there have been no House Sparrows claiming either of the two nestboxes in my yard (knock on wood). I have seen them fly over to the box, get confused and then fly off. It almost seems that they can’t figure out how to get in or they get confused….NOTE: The measurements on the drawing are just what I decided to start out at. There may be other ways to adjust the monofilament to deter the HOSP.”
Mike Ripple (above, <a#zapotocky”>Zapotocky refers to his design)
The Specifics: The fishing line itself is inexpensive 12 lb. test monofilament line that I bought at a local Dick’s Sporting Goods…tied to 3 1/2″ galvanized wood screws that are partially (about 1″) screwed into the posts on each end of the rail to which the nest box is attached. This positions the line approximately 4 to 5 inches away from the the box and 2 to 3 inches below the hole. The horizontal line is slightly further away from the hole than the vertical lines. The line is taut to the degree that the line remains horizontal, but it is not pulled so tight as to risk injury to any bird that flies into it. It has a fair amount of “give” to it. The two vertical lines are simply attached to each front corner on the box roof. In the upper right corner of the photo you can see one of the screws I used for this purpose. The lines are then pulled taut vertically and tied to the fence a few feet below the box.
The Results: On the day that I remounted the box with the monofilament line in place I watched no less than three separate male HOSP attempt to occupy this box. Each one behaved the same way. It would fly up towards the hole, act like it hit a force field of some kind when it approached the fishing line, and then fly to the ground slightly dazed. Then it would simply fly away…like magic. It was as if they couldn’t see the lines. The next morning, I awoke to the sight of a bluebird pair investigating the nest box and preparing to build their nest. They had no trouble seeing these lines…The bluebirds went on to raise four healthy young without any HOSP incidents. I originally tried the monofilament fishing line technique as shown at <http://www.zbzoom.net/~mripple/mdrive/bluebird/bb_hosp.html>. This technique worked temporarily, but the HOSP eventually figured out how to get in. I added monofilament to the roof of the box, but again they hesitated for a while and then got in. After being discouraged, I read more info on the mono technique and read of some people using taut and loose monofilament line on purple martin houses. So I decided to devise a way to place the mono on the nestbox that looks very confusing and distracting. That is when I came up with the way that is shown in the attachment.
…So far the Bluebirds have had no problem adapting to it. They initially were very curious to what it was. They did bump into it a few times, but once they figured out how to negotiate it, they flew right in (which took all of 10-15 minutes). In no time the Bluebirds were flying in and out like it wasn’t even there.
At this point, there have been no House Sparrows claiming either of the two nestboxes in my yard (knock on wood). I have seen them fly over to the box, get confused and then fly off. It almost seems that they can’t figure out how to get in or they get confused.
Sources and More Information:
- Pochop, Patricia A., Ron J. Johnson, and Kent M. Eskridge. House Sparrow response to monofilament lines at nest boxes and adjacent feeding sites. Wilson Bulletin 105(3):504-513, 1993.
- House Sparrow Control options – passive and active
- House Sparrow Control Experiments