By Nancy H. DeStefanis

Four pairs of great blue herons have returned to breed at the newly renamed Blue Heron Lake (formerly Stow Lake). San Francisco Nature Education’s (SFNE) campaigned to rename the lake after the beautiful herons who have been observed by SFNE nesting there since 1993. Three of the nests are located on the island opposite the Boathouse. Another pair has occupied last year’s nest on the island near the waterfall in the healthy tree.

Two pairs are incubating eggs. Females lay two to five eggs, then both males and females take turns incubating them. Eggs hatch 30 days later. For the first four weeks, parents take turns staying at the nest and keeping them warm at night. Each parent goes out to forage for the chicks and regurgitates fresh fish, gophers, moles and small birds into the nest. At four weeks, both parents must spend all their time feeding the chicks approximately every two hours.

At six weeks, chicks become full size at four feet, three inches. At about eight weeks, chicks begin flapping their wings. Learning to fly involves branch hopping and many test flights. Even after the chicks learn to fly, they return to the nest to be fed by their parents. At 12 weeks, all the chicks go their own way; they do not stay together as a family. Their parents split up as well.

Every Saturday, from April 13 through May 20, SFNE conducts the free program Heron Watch, at Blue Heron Lake in Golden Gate Park. Volunteers with high-powered spotting scopes show the public the chicks and explain their behavior. The program is open 10 a.m.-1 p.m. SFNE also conducts family and adult field trips each Saturday, 10 a.m.-noon. To enroll in field trips, sign up and prepay in advance. Visit sfnature.org for registration and a map of the Heron Watch program. Donations are welcome.

Nancy H. DeStefanis is the executive director of the non-profit organization San Francisco Nature Education.