A wildlife sanctuary on Bolinas Lagoon announced on Wednesday that it would delay its public season until scientists observe pairs of breeding egrets on the 1,000-acre preserve. Audubon Canyon Ranch’s Martin Griffin Preserve last year faced a complete nest failure—the first time in its 46-years history. The preserve could open as early as April 19, but only if scientists observe a minimum level of nesting, meaning 32 pairs of egrets either nesting or tending to eggs and chicks. Educational programs will be relocated to the adjacent Volunteer Canyon to reduce human impacts. “These actions will minimize human activity near the heronry, and promote natural elements of the sanctuary that may persuade more herons or egrets to initiate new nests this spring,” said John Kelly, the director of conservation science, in a press statement. In 2013, egrets arrived as usual in the preserve’s Picher Canyon, but soon nest-building faltered; not only did the preserve experience the lowest number of nests ever—32—but not one of those nests “fledged” as a result of the parents abandoning eggs or baby chicks before they could survive on their own. A report by the nonprofit Audubon Canyon Ranch found that raptors were the most likely cause of the failure, though it could not rule out human disturbance as a contributing factor.