Hi all,
We have a lot of experience with bluebirds and bluebird houses (personally, professionally, and scientifically) and there seems to be only one answer to alleviating the competition with Tree Swallows. As yes, if a Tree Swallow wants a box, it it almost always usurp it. You just need to make the swallow not want the box!
Boxes should be paired, yes, but not back-to-back. Instead, pair them on separate posts, 12-15 feet apart. Same house, same height (4-6 feet) and same direction (usually, but not always south, depends on the spot) in order to keep all variables equal. Tree Swallows will not nest that close to each other, leaving one of the two boxes free for the bluebirds. Tree Swallows have no particular concern for bluebirds as neighbors, and there's some suggestion that bluebirds actually benefit from having swallows - who aggressively mob potential predators - as neighbors. And we certainly want as many Tree Swallows to eat flying insects around as possible, so pairing boxes is a win-win.
While swallows will nest in almost any house more than 20 feet from each other, bluebirds have much larger territories. Therefore, it is usually recommended to have the house-pairs at least 100 feet apart, and preferably out of site from each other to maximize bluebird occupancy rates.
In our experience, with adequate habitat and space, there's no reason not to have up to 50% occupancy by bluebirds when pairing houses.
Other competitors, such as House Wrens and chickadees, can usually be dissuaded by placing houses at least 25 feet from dense cover.
As for House Sparrows, well, that's another question entirely. While there's lots of things that have worked well for someone in someplace, we are still desperately searching for a consistently-reliable deterrent (house design, placement, etc) for this invasive.
Hope that helps,
Derek
Sent from my iPhone
I find the same thing with my nest boxes. The swallows are more aggressive and drive off the bluebirds. I've tried providing more boxes but that just led to more swallow pairs...not necessarily a bad thing. One thing I had recommended, was to put two boxes back to back on the same post. The theory being that one pair of swallows would keep the others away, freeing up the box for the bluebirds. It never worked for me but you might have better luck. One thing I do know that will increase the number of blue birds is keeping the area well mowed. It makes a noticeable difference as the bluebirds feed close to the ground unlike the swallows. I've maintained about a half dozen boxes for 30 years now on the same 5 acre field. About one in every three years a bluebird pair will nest successfully. I've learned to be satisfied with that. Cultivating a less Augustinian view of nature is also helpful :)
On Wednesday, March 30, 2016 at 6:39:29 PM UTC-4, Allan Fuller wrote:
FOY Bluebird has been checking out a bird house. The Tree Swallows will be here in about 1-2 weeks and chase the Bluebirds out. Happens every year. Anyone have any suggestions on how to keep the Tree Swallows from hassling the Bluebirds.
About 20 FOY Eastern King Birds were eating high bush cranberries. I have never seen so many Eastern King Birds at one place at one time. They must be traveling though.
FOY Black and White Warbler hopping around the raspberry patch.
Last Sunday FOY Great Blue Heron flew up the river at tree height.
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