Hi Anthony,  (and anyone on tweeters who has Violet-green Swallows prospecting and is in time-stressed need of a nest-box and can't build or get one from a store soon enough)

Violet-green Swallows like cavities and readily take to nest-boxes and in my understanding would only nest in other situations that involving nest material being placed out in the open if under some type of stress.  I have never heard of it. The nest described sounds more like a House Finch or other species that is not a conservation concern.

 We have experienced terrible, terrible losses in the population of Violet-green Swallows in Seattle for reasons not known.

I have a few boxes designed for Violet-green Swallows and could ship you one for free tomorrow via Priority mail if you want one  and would be able to put it up.  They usually only work if placed right under the eaves. The birds like a lot of height with no close ambush-platforms near the box. If these birds have already picked a spot, go with one close to where they have picked, as the height and security issues are obviously to the birds liking. Make sure the birds, however, are Violet-green Swallows as this box is intended to only work for Violet-green Swallows.

Another possibly better option might be to not mess with them if they appear to be underway and seem to have some potential of success. It may be so late a box will only be a distraction or annoyance at this point. However, some situations can be known by humans to be untenable longterm.  Birds of this genus can be so attracted to holes they have tried to nest in the air intakes of Cessna airplanes and used to be routinely observed inspecting air-conditioning ducts of Seattle apartment buildings, back when they were a common bird in the city.

In summation, Anthony, or anyone with birds in need of a box in about two days, shoot me an email!

And thanks for writing to tweeters,

Ed Newbold Wildlife Artist
(Not an expert, and will gladly defer to anyone who is)
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