When the Cornell Laboratory of Ornithology's popular course "Spring Field Ornithology" convenes March 24, the instructor-of-record will be the same renowned biologist, author and teacher who has attracted inquisitive bird enthusiasts for 21 years.

But Stephen W. Kress doesn't take all the credit for leading the university's longest-running noncredit course. Some of his best teaching assistants, says Kress, the National Audubon Society's vice president for conservation, are up in the trees. Or on the water. Or in the air. " Spring Field Ornithology is designed to let the birds themselves be the primary teachers," says Kress of the eight-week course that offers Wednesday evening multimedia lectures and Saturday field trips. "The job of my students is simply to pay attention to what the birds are telling us through their behaviors and songs."

The Cornell lab is accepting sign-ups for either the Wednesday evening seminars, from 7:30 to 9:30 p.m., or the Saturday field trips. The enrollment fee for either the seminar series or the field trip series is $105, and the fee for both is $195. Members of the Laboratory of Ornithology are eligible for a discount.

To enroll by phone with a major credit card, the number in the Ithaca area is (607) 254-2440, or (800) 843-BIRD outside the area. To enroll by mail, send a check, payable to Cornell Laboratory of Ornithology, to SFO, Cornell Laboratory of Ornithology/AMW, 159 Sapsucker Woods Road, Ithaca, N.Y. 14850. The e-mail address is cornellbirds@cornell.edu.

The course, beginning its 22nd year, attracts people from all walks of life, including lawyers, landscape architects, homemakers and daycare providers. The only criterion is a love of birds. Students learn not only the names of birds but also come to understand why, for example, mockingbirds imitate other birds. "Mimicry has its advantages," says Kress, whose reputation as an instructor is enhanced by a lively sense of humor. "For males, it's like a badge that they can show off to attract females; for females, it's like being able to read their date's rèsumè."