The advice below seems a bit over the top. If a dizzy nestling stays
put when put back into a nest, then it would likely stay put without
the convolutions suggested. I've held my hand over nestlings and nest
cup dozens of times while banding nestlings (some old enough to
survive premature fledging should they seem unwilling to stay). By
preventing light from entering and giving the feel of being guarded
by warm hand (fake parent), for a few seconds until the birds
acclimate to being in nest again, works for all but the oldest that
might have fledged anyway [or might have actually just done so when
the well-meaning but uninformed human happened along]. These latter
would likely survive. It's a bit dangerous to attract attention to a
nest, when something less nauseating may work. In addition, not all
easily catchable young are out the nest prematurely. For open cup
nesting species in warbler to grosbeak size range, a chick can
survive at age 10 days, even if it may have required 13 or so to
fledge "naturally" -- look at the feathers on wings and body. If wing
shafts are fully "opened" [what some call "full brush"], they can
survive without our interference. Take such chicks to shrubbery near
the nest, but not in the same one in which the nest is, and let them
step onto a twig a few feet above the ground, doing everything slowly
and gently. They will eventually reply to parental noises, and make
their own especially if hungry. They don't need to be made dizzy for
our convenience or to make us feel good - Jim Greaves

At 01:02 PM 2/27/2010, tweeters-request at mailman2.u.washington.edu wrote:
>You can try returning a straying nesting to its nest by simply
>picking it up and placing it back in, then leaving so as not to
>interfere with the parents. If the nestling appears reluctant to
>stay in the nest (which is often the case if it has been startled
>out), the following technique sometimes works: hold the nestling
>firmly but gently in your hand and rotate it rapidly around as if
>you were winding up for a baseball pitch. If you do this for several
>seconds, the nestling will become dizzy enough that it will stay in
>the nest while you retreat. If you have caused a whole brood to bolt
>prematurely you will need to catch them all and spin them all at
>once to return them to the nest. Yes, it's a funny image. Yes, we're
>serious. You do not have to explain your behavior to your neighbors.