This article is from the Birds FAQ, by Lanny Chambers with numerous contributions by others.
Yes, but they must be used with great caution. Never interfere with
nesting birds, and spend as little time as possible in the nest's
Needless to say, do not touch the nest's contents.
The main North American reference is:
Harrison, Colin: _A Field Guide to the Nests, Eggs, and Nestlings of
North American Birds_ (published by Collins, 1978).
Be sure to read this book's introductory text; don't skip right to the
If you have an interest in nests and eggs, the FAQ editor suggests that
you seek out and get involved with an organized bird survey.