This article is from the Birds FAQ, by Lanny Chambers with numerous contributions by others.
If you saw it on private property, seek the property owner's permission
before publicizing it. See "ETHICS FOR BIRDERS," below.
Assuming that you've received permission, or if the bird was seen on
public lands, post a report to rec.birds, of course. Include a complete
description of the bird; the date, time, and location of the sighting; the
names of those who saw it; and whether photos were obtained.
In North America, you can also call the North American Rare Bird Alert
(U.S. and Canada: 800-458-BIRD). You can also call the regional
rare-bird hotline; North American numbers are published regularly
in _Winging It_ (see the bird magazine list in the other part of the FAQ).