Last year, Rusty Scalf, teacher and trip leader for the Audubon Society, introduced me to a family of western bluebirds living and nesting in Berkeley’s San Pablo Park. This year, Scalf called me back. Apparently, a “mad man” had flown onto the bluebird scene.
“He’s like a Rambo,” Scalf said. “A worm bandit… a total behavioral outlier.” “He,” the bluebird shown above, was a fledgling, a few weeks old, which undertook intensive hunting forays across the park. He even “mugged” a house sparrow and competed with his parents, beak-to-beak, for insects and worms — food he delivered to his younger brother and two sisters in the nest.
The male delivered these wiggling meals for weeks — initially, while the chicks were growing in the nest box, and later, after they had fledged and taken up residence in the trees. Successful pairs of western bluebirds may produce two broods in one season. It’s a special bonus when one of their older offspring (almost always a son) helps tend the younger chicks.
This behavior — a form of “helping” — is rare. According to Professor Janis Dickinson, Director of Citizen Science at The Cornell Lab of Ornithology, an average of 7 percent of western bluebird pairs receive extra help in tending their nests. Worldwide, only 3 percent of bird species are so-called “cooperative breeders.”
Feedings by young bluebirds, however, do not provide chicks with a net gain in calories, Dr. Dickinson said.
One theory, instead, is that sons tend to the younger chicks as a form of “rent” — of paying back their hard-working parents for living at home and pecking food in their territory. Most sons spend their first winters with Mom and Dad. Daughters disperse by fall.
Western bluebirds help as adults, too. Grown-ups tending nests not-of-their-own are exclusively male. Their mates may have died, or their nests may have failed.
They then turn their efforts to family members — their parents, brother and sister-in-law, maybe grandpa and his mate — providing extra meals to their chicks. If these chicks grow faster and leave home sooner, Mom and Dad might get a chance at a second brood.
To understand why a bird might pour its time and energy into another bird’s chicks, Dr. Dickinson said that scientists perform a special form of “accounting.” They look at an animal’s options and whether the behaviors it employs offer best advantage.
“We talk about inclusive fitness,” she said, “the combined fitness achieved by surviving and producing one’s own offspring, plus the fitness one gets by increasing the number of offspring that relatives produce beyond what they would achieve without your help.”
Given the choice, bluebirds would rather do the breeding themselves. But like the old adage says — if you can’t breed ‘em, join ‘em.
Western bluebirds actually switch their diets, from bugs in summer to berries in winter. No one knows, for sure, where Berkeley’s bluebirds go after they leave their nesting areas, like San Pablo Park, in the fall.
Scalf has occasionally spotted small bluebird flocks in yards around the city, gorging on crops of winter berries. They seem to take a particular liking to catony aster berries, pyracantha berries, Himalayan blackberries, and a few that people cultivate for themselves. Yes, bluebirds on blueberries!
City bluebird, country bluebird
Oak woodlands, mixed with bug-filled meadows, offer an ideal habitat to western bluebirds in California. Most, in fact, live in rural settings. Dr. Dickson has studied western bluebirds and their cooperative behaviors since 1989 at the University of California’s Hastings Natural History Reservation in Carmel Valley.
But it only takes few bluebirds to spread happiness. Every time I stroll through San Pablo Park with my big camera and Rusty Scalf (“the Bluebird Guy”), people spark up a conversation. They marvel at the bluebirds, their lightness and color, the importance of small glittering things.
How to help western bluebirds:
- Keep pet cats (predators) indoors.
- Refrain from using pesticides; they kill the crawlies that bluebirds eat.
- Protect old-growth oak trees, the natural habitat and feeding grounds for western bluebirds.
Special thanks to Dr. Janis Dickinson (Cornell Lab of Ornithology), Vincent Voegeli (Hastings Natural History Reservation), and Rusty Scalf, who praises the Golden Gate Audubon Society for its work in bird conservation.