In article , TheScullster
writes
We have one or two red squirrels around.

Lucky, lucky, you )

Will they put off the birds?

I don't think so.
It is the grey squirrels that rob nests.

How high should a bird box be mounted?

High enough so that the local feline population can't get to it!!
6-12 feet up but away from any overhanging 'access' branch should do it.
--
Jane Ransom in Lancaster.
I won't respond to private emails that are on topic for urg
but if you need to email me for any other reason,
put jandg dot demon dot co dot uk where you see deadspam.com