Just before my shift started, I walked into the baby bird room at the wildlife rehabilitation center. A distinctive sound ringing through the room—”WEE-urrr, WEE-urrr”—transported me back more than five years and 1,000 miles. The soundtrack of late summer in the pinyon-juniper habitat of our previous home in the Colorado mountains—baby Black-headed Grosbeaks were in the house!
Structurally, an adult Black-headed Grosbeak stands out. Its large, egg-shaped head features adark, supersized, finchlike beak with a down-curving upper beak (called the mandible). Attached to a stocky body, the tail seems just a tad too short for the bird. An adult male in breeding plumage stuns the eye with his burnt-orange body; black head, wings, and tails; and
white bars slashing through the wings. Non-breeding males, females, and immatures display shadow versions of the breeding male’s pattern, with streaky gray-brown upperparts and buffy to butterscotch underparts; fine dark streaks slide down the sides and flanks. Even in this duller plumage, the distinctive head pattern, accented by a buffy eyebrow, makes the bird seem to be wearing dark goggles. As the bird flies off, a surprise yellow patch under the wings (called the underwing coverts) flashes.
Officially entitled Pheucticus melanocephalus, the species name seems obvious—from Greek for “black” (melano) and “head” (cephalus). The genus name derives from the Greek pheuktikos (“inclined to be shy), reflecting the typically stealthy nature of these birds. Both components of the common name offer no surprise. “Grosbeak” derives from French for “large beak,” which indeed they have. And “black-headed”—well, just look at that male in breeding plumage.
That eponymous massive beak well equips a grosbeak for cracking seeds of all sizes. But that beak serves just as well for crushing hard-bodied insects or even snails. Insects (especially beetles), spiders, and other animals make up about 60% of Black-headeds’ breeding-season food; fruits and seeds account for most of the rest. They can also cautiously visit sunflower seed feeders. Where their range overlaps with wintering monarch butterflies, grosbeaks eat large numbers of these insects. Toxins in monarchs make them poisonous to most birds, but not these birds. The birds feed on the butterflies in roughly eight-day cycles, which may give the birds time to eliminate the toxins. Grosbeaks also pull off and discard the wings, which contain the greatest concentration of the toxins—perhaps another aspect of limiting their ingestion of toxins. Interestingly, Black-headeds also consider poison oak berries a delicacy. No accounting for taste…
Black-headed Grosbeaks inhabit most of San Diego County’s coastal slope. As habitat generalists, they typically choose some kind of woodland; here, preferences include oak and riparian woodlands. The species ranks as one of San Diego County’s most reliable returning migrants, with birds arriving in the last few days of March. Unlike many other songbirds, the showy male contributes equal time to the home front: Although only the female builds the nest, both sexes incubate eggs, feed the young, and vigorously defend their nesting territory. Clutch size ranges from two to five eggs, with three as the most common. Babies hatch after about two weeks; they crawl out of their nests to perch in trees 10 – 14 days after hatching—a good two weeks before they can fly! The babies hunker down silently on tree limbs in the thickest cover available near the nest, apparently purposefully not associating closely with siblings. The parents note the youngsters’ positions and continue to feed them. Once the fledglings can fly, though, they become harder to keep track of and the young abruptly become more vocal—cue that incessant “WEE-urr” begging calls for a couple of weeks until the fledglings become independent.
Adult males head for their wintering grounds in Mexico earlier than females do, starting in late August. The juveniles often linger longer, leaving several weeks after the last adult has departed, making Black-headed Grosbeaks among San Diego County’s longest lingering migrants.
In the western U.S., especially in areas where American Robins disappear for the breeding season, the sweet song of the Black-headed Grosbeak caroling down from the treetops serves
as a familiar harbinger of spring. The male’s song actually resembles that of an American Robin that took voice lessons—a rich, carefree serenade of whistled two-note phrases that alternate between high and low. Between this lilting song beginnings early in April and the fledglings’ easy-to-identify begging calls as summer draws to a close, the vocalises of the Black- headed Grosbeak bookend the heart of songbird breeding season.