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HARVARD — In conjunction with the Harvard Conservation Trust, the Warner Free Lecture Trust is will present world-renowned ornithologist David Allen Sibley on April 7, at 8 p.m., at the Unitarian Church, 9 Ayer Rd.

Sibley will speak about the universal appeal of birds and the pleasures and challenges of creating a field guide about them. He is the author of the fastest-selling bird guide of all time, “The Sibley Guide to Birds,” a comprehensive field guide to North American birds published in October 2000.

More than 10 years in the making, “Sibley’s Guide to Birds” is a monumental achievement that includes 6,600 beautiful watercolor illustrations covering 810 species in North America with clear, descriptive text.

Since the book’s publication, he has also published several regional guides which are the new standard for use in the field. These guides include more that 4,000 illustrations with descriptive text concerning frequency, nesting, behavior, food and feeding, voice description and key identification features.

Sibley, the son of well-known ornithologist Fred Sibley, began seriously watching and drawing birds in 1969 at age seven. He began formulating his design for bird identification guides when he was in middle school. However, it took years of field experience and research for Sibley to make his guides a reality.

In pursuit of that quest he has written and illustrated articles on bird identification for Birding and American Birds — now Field Notes — as well as regional publications and books including “The Wind Masters,” “Hawks in Flight,” and “The Birds of Cape May.”

Since 1980, David has traveled the continent watching birds on his own and as a professional tour leader.

Sibley is the recipient of the Roger Tory Peterson Award presented by the American Birding Association for a lifetime of achievement. A native of upstate New York, Sibley’s search for birds has taken him to such birding hotspots as Cape May, N.J.; the Lower Rio Grande Valley of Texas; and southern Florida. Although he still travels extensively, he calls Concord, Mass., home. There he lives with his wife and two sons.

There will be refreshments following the lecture and the trust will have an information table with more information on Harvard’s trails and conservation resources. The lecture is free to the public.

For information, or to be added to our e-mail announcements about future lectures, call (978) 456-8865 or e-mail rachel91@charter.net.