Naturalist’s Notebook: Overworked Bushtits

8 June 2009, Tillie Creek Campground, Kern County, California

Upon hearing vaguely familiar trilling notes coming from a coffeeberry bush, I pause to investigate. My attention is drawn to the delicate trembling and twitching of foliage, and I glimpse a small bird hopping about within. I produce a series of soft pishing sounds, which draws a Bushtit briefly into view, but it quickly resumes its energetic foraging in the tangle of foliage.

Satisfied that this is the source of the trilling notes, I am about to leave when a fledgling cowbird hops from the bush onto a nearby boulder, where it perches and emits the very vocalizations that had initially caught my attention. Its stubby wings and tail indicate that it fl edged very recently.

I scarcely have time to ponder the thought of what species of bird had the misfortune of having this chick foisted upon it, when a tiny, somewhat haggard Bushtit, with a beakfull of minute insects, hops down and delivers them to the begging cowbird! It is mildly alarming to watch as the Bushtit inserts its head right into the cowbird’s gaping maw, placing the food well back into its mouth. It looks like the tiny Bushtit is in imminent danger of being accidentally gulped down, but the cowbird politely receives the food without incident, after which, the Bushtit quickly flies off to find more food.

I linger to observe five more feedings and to ponder questions such as: How did the cowbird lay an egg in the Bushtit’s sock-like nest? How did the tiny Bushtit cover and warm an egg weighing more than half its own weight? How did the pendant nest hold together through the stresses of a large chick shifting about within it? What was the cost in energy to the overworked foster parents, having to ceaselessly shuttle very small insects to the hulking chick? And what happened to the Bushtit’s progeny? There can be little doubt that if there were any young Bushtits they perished shortly after hatching.