Environment : Notes about your surroundings.

ON THE WING: Migrating birds are flying through the county as they make their way to points north for the breeding season. The annual spring migration is “pretty much at its peak right now,” says Sylvia Gallagher of the Sea and Sage Audubon Society.

The migrants typically pass in waves through the county around this time, Gallagher said. Some migrants that might be seen in suburban neighborhoods include the Wilson’s and Nashville warbler, ash-throated flycatcher, black-headed grosbeak, western wood-pewee, warbling vireo and Swainson’s thrush.

Another bird that should be arriving soon is the yellow-and-black western tanager. “It’s a very flashy bird, so people want to know what it is,” Gallagher said. In the breeding season, the male’s head is a bright red.

Generally, the same shore bird species as in winter are seen in the county now. They present an extra challenge for birders to spot, however, as many are between their winter and breeding plumages. California least terns are beginning to arrive in the county; populations of this endangered species nest at Upper Newport Bay, Bolsa Chica and Anaheim Bay.

FOR CHILDREN: A new series of after-school Science Adventures classes starts this week at the Fullerton Arboretum on the Cal State Fullerton campus. The courses, open to children in grades 1 through 6, meet 1 hour a week for eight weeks. Topics include insects and rocketry. The fee for each class is $48. Science Adventures also will offer a series of summer classes. For information, call (714) 895-3966.

BACK BAY: “Bicycling the Bay but Not Walking on Water,” beginning at 11 a.m., is today’s program at the Upper Newport Bay Ecological Reserve. Two programs will be offered Saturday: a nature walk at 9 a.m., and “Early Plant Uses” at 1 p.m. There is a $2 fee. For information, call (714) 640-6746.

BUGGED: “Insects of Oak Canyon” is the title of Saturday’s program at Oak Canyon Nature Center in Anaheim Hills. The program begins at 10 a.m. For information, call (714) 998-8380.