By Millie Basden
“I miss the changing seasons” is a lament often expressed by San Diegans who have moved here from more northern climes. At a latitude of roughly 32 degrees north, San Diego lies within the subtropical zone of our planet. Without the frosty nights of temperate areas, our deciduous trees are not triggered to change colors like they are up north.
The leaves of our native maple tree, boxelder (Acer negundo), found along the San Diego River in Mission Trails Park, turn yellow before falling to the ground. Western sycamores (Platanus racemosa) and Fremont’s cottonwood (Populus fremontii) may also show fall colors, or the leaves may just turn brown and then drop. These subtle hues do not thrill folks in the same way as the vibrant palette of a New England autumn.
But changing leaves are not the only indication that fall has arrived with winter soon to follow. I find satisfaction in another source that tells me the seasons have changed: the arrival of white-crowned sparrows and yellow-rumped warblers.
These two birds are not closely related. As their names suggest, one is a mostly seed-eating sparrow and the other, a mostly insect- and fruit-eating warbler. What they share, however, is the distinction of being the most abundant birds in San Diego, including in Mission Trails, during the winter months. Except for an occasional straggler, they are completely absent from coastal San Diego beginning sometime in May until September.
White-crowned sparrows (Zonotrichia leucophrys) are one of our larger sparrows, stretching about 7 inches from the tips of their beaks to the tips of their tails and weighing about an ounce. Male and female white-crowned sparrows look alike. The adults have black and white stripes on the top of their heads. During their first year of life, the head stripes are brown and off-white. At all ages, this sparrow has a light-colored (dark pink or yellow) cone-shaped bill. Like most sparrows, they often feed on the ground and will flush to nearby bushes or trees when disturbed.
Male white-crowned sparrows sing year-round. Various mnemonic devices have been suggested to help humans recognize the song. To my ear, it sounds like they are singing, “Oh, my, what to do.”
When they leave our area each spring, white-crowned sparrows head north as far as subarctic regions of Alaska and Canada.
Yellow-rumped warblers (Setophaga coronata) are also large for a warbler, stretching about 5.5 inches from the tips of their beaks to the tips of their tales, but weighing only about half an ounce. True to their name, the grayish birds always have a yellow rump patch. Depending on age, sex, and season, they may also have yellow on their throats, flanks, and top of their heads, along with dark streaks on their undersides and backs. Males in breeding plumage add contrasting black patches to their chests and heads. Their thin bills are always dark.
Yellow-rumped warblers are often seen foraging through the leaves of trees or bushes, seeking insects and fruits. They also sally out like flycatchers, grabbing insects on the wing.
The most frequently heard vocalization of this warbler during winter is its insistent call, which can be described as “chep” or “chup.”
Yellow-rumped warblers spend the breeding season in coniferous forests, mostly to the north of San Diego County, but breeding has occurred in our highest mountains.
Look around you. Enjoy the white and yellow markers of the season. The white crowns of sparrows and the yellow rumps of warblers will only be with us for a few months. When they arrive each year, you know the season has changed at 32 degrees north.
—Millie Basden is a trail guide at Mission Trails Regional Park.