After I park my car in the lot outside the Davis branch of the Yolo County Library I can’t help but notice more than a dozen small birds eating something on the ground beside the lot. I look closely at one of the birds and notice four patches of yellow among the gray, black, and white feathers—one on the throat, two more on the flanks, and the third on the rump. These markings belong to the yellow-rumped warbler (Setophaga coronata), one of my favorite birds. I know there’s a fifth spot of yellow on top of the head, not always visible. The black and white colors are subtle highlights, not high-contrast patches, so I tag these birds as the Audubon’s sub-species and not the Myrtle’s, both of which can be found around Davis in the winter. The distinction matters: these Audubon’s warblers will migrate the relatively short distance into the Sierra Nevada to breed whereas any Myrtle’s warblers in the area will fly all the way to the boreal forests of Canada. Of the two, the Myrtle’s can adapt to a greater variety of habitats, but the Audubon’s is more common in Davis.

And what, I wonder, are these dear little birds eating? It is the reddish-pink berries from the deciduous Chinese pistache tree, several of which are growing next to the parking lot. Although native birds in California tend to prefer native plants, many enjoy feeding on certain non-native plants and their fruits and seeds. The non-native Chinese pistache (Pistacia chinensis) seems to have been adopted by the yellow-rumps as an important food source. It’s probably a smart choice on their part as Chinese pistache is one of the most common trees in Davis. In 2018, it made up 6.6% of the city’s tree population. I wonder if the City of Davis landscapers knew they were making foraging habitat for my little friends when they planted these trees.

To be sure, berries—native or not—are not the warbler’s favorite food. Their relatively long and narrow bills, along with their great agility in tree branches, attest to the fact that they are primarily insectivores. In spring and summer and fall, yellow-rumped warblers delight in picking off gnats, spiders, scale insects, weevils, fly larva, and beetle larva from leaves, twigs, and branches. They switch to berries only when insects become scarce. That doesn’t mean they don’t enjoy the berries.

If you visited my house, you’d find evidence of my fondness for yellow-rumped warblers. On my kitchen windowsill—right in front of me as I do the dishes after dinner—is the likeness of a yellow-rumped warbler carved out of wood. He is perched there so life-like that I often forget he is not alive. He came into the world through the skilled hands of master carver Chester Wilcox, who I met at the Central Valley Birding Symposium in November. When attendees first gathered at the Hilton Hotel in Stockton, I was drawn to his vendor table and spent a long time admiring his exquisitely carved birds, each a perfect representation of its species, down to the finest detail. After going on several field trips beginning at the crack of dawn—and seeing yellow-rumped warblers at many locations, among the trees near the enormous flocks of overwintering waterfowl—I went back to Chester’s table and bought the yellow-rumped warbler perched on a conifer branch.

It’s not like I don’t see enough yellow-rumped warblers. They show up almost everywhere I go around Davis in the winter. Along the bike trail, in front of Shields Library, outside the Davis Food Co-op, I hear their constant chit chit chit and see them foraging among the shrubs. I so enjoy their ebullient energy. Noted ornithologist William Leon Dawson must have had similar experiences a century ago, because in 1923 he declared, in his Birds of California, that the yellow-rumped warbler was “Par excellence the warbler of the West.”

But in Davis yellow-rumps exhibit their iconic status only during the coldest months. Because many other birds depart this region of California in the late autumn, just as yellow-rumped warblers seem to become ubiquitous, the bird reminds me of the winter season as much as the rain, the leafless trees, and the fallow fields. As I adjust to the colder weather by bundling up, the yellow-rumped warblers seem to rejoice in the relative warmth, having come down from the mountains to escape the snow flurries and steep drops in temperature.

I am a little sad when the Audubon’s yellow-rumps bid the Central Valley farewell in the spring and migrate upslope to the conifer forests of the Sierra Nevada to breed. But I can picture birds I see in Davis pairing up once they reach the sub-alpine forest and building nests 50 feet up in limber pines. I see them as my little feathered emissaries, giving me the vicarious pleasure of being in a place I know well but visit too infrequently.

I know the warblers’ winter sojourn in Davis is important in the bird’s life cycle. They need good nutrition to maintain their vitality so that when they migrate to the Sierra they are ready for the energetically demanding tasks of finding mates, building nests, laying and incubating eggs, and feeding young. Non-native berries like those of the Chinese pistache are abundant in Davis in the winter, but given the paucity of protein-rich insects, I wonder if the non-native berries provide adequate nutrition.

With this concern in mind after I bought my house some years ago and began re-landscaping with natives, I thought about what kinds of native vines, shrubs, and trees would have provided berries for yellow-rumped warblers before non-Indians settled here and planted many kinds of non-native trees. It seemed to me that wild grapes would have been a primary winter food source back in those times. I’ve read accounts of white explorers and settlers in California that mention thick vines growing high into the trees in riparian zones. Many of these must have been the wild grapes (Vitis californica) native to California. In 1837 and again in 1839, British naturalist Richard Brinsely Hinds explored the waterways of the Sacramento Valley and recorded in his journal that “Great quantities of grape vines loaded the trees on the riverbanks.”

I was certainly predisposed toward grapes anyway. I remembered Henry David Thoreau’s descriptions of paddling down the Concord River in Massachusetts and seeing fox grapes (Vitis labrusca) climbing up the trees growing on the riverbank. As a child in Dayton, Ohio, I often enjoyed sandwiches made with peanut butter and Concord grape jelly (and learned many years later that the concord grape was a hybrid between Thoreau’s wild fox grape and the wine grape [Vitis vinifera] of Europe).

So, I planted a wild grape (Vitis californica) vine along my fence in the front yard that I purchased from the UC Davis Arboretum plant sale. I had dreams of the vine wandering up into the nearby Irish strawberry tree and toyon shrub and even climbing higher into the valley oak tree in the park just on the other side of my fence. That was fifteen years ago. About three years ago the grape finally made it into the valley oak. Whenever I look up at the high-roaming vines in the oak I think of Hinds’ journal passage and the lush landscape of California before European colonization.

Early this winter, I kept watching to see if the yellow-rumped warblers would partake of the shriveling grapes hanging from the vines twined among the branches of the valley oak. Sure enough, they did. It was an exciting moment. Then I saw yellow-rumped warblers, along with robins and mockingbirds, feasting on the elderberries drying on my eighteen-foot native elderberry tree. It gave me a deep sense of connection and purpose to be providing birds with food and habitat.

Recently I picked the persimmons from the tree that grows not far from the wild grape and elderberry. I decided to leave a few for the birds. As I walked back to the house with the basket of fruit, I shouted to the warblers “here is more food for you!” They soon found the fruit and indulged, pecking deeper and deeper into the soft flesh.

References

Bent, Arthur Cleveland. 1963. Life Histories of North American Wood Warblers Part One. Dover Publications, Inc., New York, N.Y. Republication of the Smithsonian Institution United States National Museum Bulletin 203 published in 1953.

Dawson, William Leon, 1923, Birds of California, Volume 4. San Diego: South Moulton Co.

Farris, Glenn. 2015. A British Naturalist in California in 1837 and 1839: The Journal of Richard Brinsely Hinds. Boletin: Journal of the California Mission Studies Association Vol. 31(1).

Thoreau, Henry David. 2000. Wild fruits. W.W. Norton & Company. New York, N.Y.

Edited by, Eric Engles.