The Western Tanager joins several other species of birds gleaning insects from the leaves, branches, and trunk of the Eucalyptus tree. I saw this male Tanager doing some short range fly-catching, as well.
Fuzzy fibers just visible on the tip of the Tanager's beak provide us with an important clue to the Tanager's activity in the Eucalyptus trees.
The Eucalyptus trees are not native to California, and some people don't like them, but these trees provide shelter and nutrition for a wide variety of birds. A peculiar type of insect larvae constructs little domes made of fuzzy material on the Eucalyptus leaves, and some birds feast on these.
Birds seen feeding on insects and/or lerps on the Eucalyptus tree include Anna's Hummingbird, Yellow-rumped Warbler, Yellow Warbler, Lesser Goldfinch, House Finch, House Sparrow, Bullock's Oriole, Black Headed Grosbeak, Western Tanager, Bushtit, Hermit Thrush and Western Kingbird. Other birds such as White-winged Dove, Northern Mockingbird, American Kestrel, and the American Robin have been seen perched in the row of trees.