Nature books based on PBS series; The Flight of the Condor: A Wildlife Exploration of the Andes, by Michael Andrews. Boston: Little, Brown & Co. 158 pp. $22.50.; The Discovery of Animal Behaviour, by John Sparks. Boston: Little Brown & Co. 288 pp. $24.95.

These two books are companions to the current PBS television series ''Nature, '' produced by the BBC's famed natural-history unit. The series began in October with ''The Flight of the Condor.'' The episodes composing ''The Discovery of Animal Behaviour'' will close the series in January.

''The Flight of the Condor'' not only describes the geography and wildlife of South America, but also the author's adventures while filming the series. Aided by plenty of excellent photographs, he offers us superb armchair exploring.

The beguiling quality of this book for nature enthusiasts becomes apparent in just a tiny sample of the scores of unfamiliar animals, birds, and plants described - Magellanic penguins, the flightless steamer duck, the kelp goose, the giant fulmar, guanacos, coscoroba swans, the thorn-tailed rayodito, the huemul, coicopihue flowers, and the huet huet.

The Andrews stories, dappled with such names, reveal what the wonderful shots in his television series do not: the extraordinary effort required to photograph condors soaring, jungle hummingbirds drinking, or pumas leaping. His star cameraman, Hugh Miles, returns after a typical day's exercise in patience, ''having spent twelve hours sitting behind his camera concentrating every second in case he missed an otter. He reported that he has got two or three good shots.''

More than half of the book, as the team travels north from the tip of Cape Horn, is devoted to ecstatic praise of remote, unspoiled places and wildlife seldom seen. Yet Andrews ends by mourning how men have often marred the earth. The Amazon rain forest is vanishing ''before we have learned even half its secrets,'' Andrews writes sadly. His closing words: ''I hope 'The Flight of the Condor' will not become simply an historical record of all that has been lost.''

''The Discovery of Animal Behaviour'' gracefully condenses the story of how and what man has learned about animals. The scope of the Sparks book is larger than that of Andrews, for Sparks draws on the study of all animal behavior throughout history.

The photos are yet more stunning than the ones in the Andrews book. They match the best of nature photography in the past 10 years. Where was there ever portrayed a more perfect leap than in the photograph here of a green tree-frog? Such arresting color photographs face almost every page of text.

Sparks surveys the lives and work of important zoologists, uncovering ''some of the strange circumstances which led to many major discoveries.'' His language often possesses the polish and metaphors of literature, as, when describing a tropical spider whose web is invaded by a smaller thief spider, he writes, ''. . . Unknown to her, another actor shares her silken stage.''

How has man's understanding of animal behavior changed? The ways are as vast as the historical period and locale of the observer.

For example, Sparks notes that for thousands of years the Indians in the Pacific Northwest depended for their livelihood upon the annual migration of salmon. To these fishermen, the salmon's arduous journey up fast-flowing rivers to their fresh-water spawning areas, seemed to be designed for the benefit of man ''rather than for the fish themselves.''

Europeans in the middle ages conceived of nature as a text conveying messages ''for the eyes of the faithful.'' In the 13th century, Frederick II, Holy Roman Emperor, was a great naturalist who didn't just read and copy bestiaries, but actually observed birds. This contrasts markedly, Sparks points out, to the rarity of direct and faithful observation in books for centuries after Aristotle.

Sparks shows us that even by the 19th century, the English eccentric and naturalist Charles Waterton was unconventional in believing that the best place to study animals was in their ''native haunts.'' At the time, the ''zoological fashion was to shoot everything on sight and to study the specimens at leisure in museums,'' Sparks writes.

The author also retells the story of such giants as Charles Darwin, whose studies revolutionized our view of earth's development. He writes, too, of such lesser-known figures as Lewis Henry Morgan, whose work on the American beaver was ''the most thorough study of a single species ever undertaken at the time.''

Deciphering signs and signals, such as the courtship gestures of birds or the directional dances of bees, unraveling reasons why animals sometimes cooperate rather than compete - all these stories belong to Sparks's narrative. And never far away is the longing to understand ourselves better. ''Research into animal behaviour has reflected an increasing preoccupation with the necessity to understand the roots of our own behaviour,'' Sparks notes.

I can think of no more readable summary than this book offers of the way in which man's delight in animals grew into a science.