GIFT BOOKS IN BRIEF : CAMBRIDGE ENCYCLOPEDIA OF ORNITHOLOGY, <i> edited by Michael Brooke and Tim Birkhead (Cambridge University Press: $49.50)</i> .

Even in the field of the traditionally “user friendly” popular bird books, this is an outstandingly rara avis --a volume with beauty and brains .

Its understated goal, as declared in the introduction--”to stimulate interest . . . in the study of birds”--succeeds so well that readers who think they only want to know why geese fly in V-formation, or whether a partridge would in fact spend time in a pear tree may find themselves engrossed in all 362 pages of this intriguing survey.

Not that this is dumbed-down science or another pretty-bird picture book. The text, organized under such chapters as “navigation and migration,” and “birds ancient and modern,” is rich in concept and heavy with scientific nomenclature, but not off-putting. The terms are defined as they appear, and the contributing authors lay out what is known and not known about these remarkable creatures with restrained relish, eager to share rather than pontificate.

Since it could crane its neck to look up, humankind has always marveled at birds--their flight, their plumage, their songs. In trusting the intelligence and honoring the curiosity of a general readership, this book accomplishes the double feat of explaining the complexity of their wonder without sacrificing the wonder of their complexity.