I've found mounting a large box or any box high in a tree is difficult and best done by two people, even if the other person is simply holding the bottom of the extension ladder. I've placed a couple of flying squirrel boxes up in trees by myself and still look up at them and shutter.

To temporarily secure the large box while you lag bolt or otherwise attach it to the tree, drill a small hole in the back of the box, pound a 16 penny nail into the tree at the desired height, and then hang the box from the nail. Note that this is not intended to hold the nest box in place any longer than it takes you to secure it properly.

For more info and for nest box designs for birds, bats and other mammals, see http://wdfw.wa.gov/wlm/urban/ and click on the link to Nest Boxes for Birds and Fun Projects for Urban Wildlife (Note: I've had Townsend's chipmunks nesting in a Douglas squirrel/Flying squirrel box for several years).

Happy Habitating,

Russell Link
Urban Wildlife Biologist
Dept. of Fish and Wildlife
16018 Mill Creek Blvd.
Mill Creek, WA 98012

(425) 775-1311 ext. 110
linkrel at dfw.wa.gov
www.wa.gov/wdfw