I have been building and installing nestboxes made from
unfinished cedar fencing materials for 15 years. I have had
no trouble with bird dying from asphyxiation, I have never
read of this in the refereed journals that regularly discuss data
collected from nestboxes. Natural cavities are often built
in cedar and other species with even higher turpine content.

I'm going to go out on a limb and guess that the sight
suggesting this was selling nestboxes made out of something
(probably plastic) other than cedar.

I recommend, however that you build your own. A 5 foot
1" x 6" costs about $2.00 and is enough for one box. You
can find free instruction for the box I use at:
http://home.pacifier.com/~mpatters/bird/nestbox.html

Jacki Bricker wrote:
>
> I've been doing research on the web about nest boxes, and have encountered
> some conflicting information. My husband and I just ordered three cedar
> nest boxes of appropriate dimensions, etc., to attract (hopefully)
> swallows to our acreage.
>
> Several websites either sell nest boxes of cedar, or say when building
> one, to use woods such as cedar or cypress. But I encountered another
> website that said that the natural outgassing of the cedar wood can
> asphyxiate the young. Is this true?
>
> Can any experts out there lend some advice? We need to cancel the order
> very soon if cedar is bad for them. Thanks.
>
> -Jacki

--
Mike Patterson Alas, to wear the mantle of Galileo,
Astoria, OR it is not enough to be persecuted
celata at pacifier.com by an unkind establishment,
you must also be right.
---Robert Park
http://www.pacifier.com/~mpatters/bird/bird.html