The Cuckoo in the Coal Mine

Yellow-billed Cuckoos (Coccyzus americanus) are fairly common in the eastern U.S. But in the last half-century, they have become rare in the West. Over the past 10 years in San Diego County, eBird shows unique sightings only 15 times—almost always a single bird in June or July, at Lake Henshaw, Lake Hodges, the Anza Borrego Desert, or several locations along the San Luis Rey River. One well-documented bird spent at least nine days along the Otay River. The most recent sighting was noteworthy. The bird appeared last October on a patio in the Del Mar area. Under a window. Dead.


Why write about such an infrequently seen bird?  Because perhaps the only thing rarer than a sighting of this species here is a supportive ruling from the U.S. Fish and Wildlife Service (USFWS) on behalf of a dangerously threatened species. And therein lies the tale.


A large, slender, tube-shaped, brown-backed, white-bellied bird, a Yellow-billed Cuckoo features an eponymous down-curved, thrasher-like bill that is yellow on the bottom. Its face hints at a dark mask through an eye with a yellow eye-ring. Bold white spots on the long tail’s underside are often the bird’s most visible feature on a shaded perch. Furtive, retiring, and watchful by nature, this bird’s presence may be first revealed by its distinctive wooden call:  a low clucking that starts fast and insistent but seems to lose both speed and interest by the end.


The Yellow-billed Cuckoo is a sedentary, shop-and-go skulker that can spend minutes on end on the same perch, moving only its head in slow, wandering turns to study the foliage around it before flying to another perch. Much to the chagrin of eager birders, the bird often stays well hidden in shadowy deciduous woodlands, sitting stock still and even hunching its shoulders to conceal its crisp white underparts, as it scans for large insects (e.g., caterpillars, cicadas, grasshoppers, crickets). It also occasionally eats small frogs, arboreal lizards, or eggs and nestlings of birds.


In California, the Yellow-billed Cuckoo breeds primarily around the Sacramento Valley, Kern River, Lower Colorado River and a few locations in Owens Valley and southern California (although not in this county). The breeding behavior of the Yellow-billed Cuckoo is peculiar in several ways. Although they commonly raise their own young, Yellow-billed Cuckoos and their congener, the Black-billed Cuckoo, are the only known facultative (optional) brood parasites among altricial birds (compared to an obligate brood parasite such as the Brown-headed Cowbird). In addition, the cycle moves fast—as few as 17 days from egg-laying to fledging. They typically lay 2–3 eggs. Most songbirds lay one egg a day until the clutch is complete. For these cuckoos, though, the period between eggs can stretch to five days. Incubation requires 9–12 days. These youngsters grow on overdrive:  Once they hatch, they gain half their adult weight in their first four days. Fledging occurs in a mere 7–9 days. As a result of the asynchronous egg-laying and this meteoric development pace, the oldest chick can be close to leaving the nest when the youngest is just hatching. If food runs short, the male may remove the youngest chick from the nest. Even if the youngest lives, though, it may simply be left behind when its older siblings leave the nest. Nestlings fledge still flightless—a whopping 10 days before they can fly—but they agilely climb and clamber around in trees while they figure out the world of flight.


In western North America, the Yellow-billed Cuckoo lives only in extensive stands of mature riparian woodlands. The cuckoo requires the largest intact stands of any of California’s riparian birds:  at least 100 acres (preferably 200 acres). That’s a lot of land—and land that humans also covet. Danger, Will Robinson—danger!


Danger indeed. Yellow-billed Cuckoos have already been extirpated from British Columbia, Washington, and Oregon. Statewide breeding populations in Idaho, Wyoming, Colorado, Utah, and Nevada number only 5−20 breeding pairs. From 15,000 breeding pairs less than a hundred years ago, California’s Yellow-billed Cuckoo population has dropped to 40−50 pairs. New Mexico currently hosts 100-155 breeding pairs; and Arizona boasts the largest breeding population, although still only 170-250 pairs.


This collapse of the western Yellow-billed Cuckoo population group has resulted primarily from the wholesale destruction of riparian woodlands, which now cover only a small percentage of their original expanses. Habitat fragmentation and pesticides have added to the severe declines. Listed as Critically Imperiled, Endangered by the California Department of Fish and Wildlife in 1971, until recently this critically imperiled western group had received no federal protection due largely to taxonomic controversy surrounding the validity of its subspecies status. After almost 30 years of petitioning, though, the USFWS designated the western Yellow-billed Cuckoo a distinct population segment (DPS, defined by geography rather than taxonomy). USFWS granted the DPS protection as “threatened” under the federal Endangered Species Act (ESA) in October, 2014.


Yet in 2017, a coalition of mining and ranching industries and other business interests favoring private property rights petitioned the USFWS to remove ESA protections from the western Yellow-billed Cuckoo as part of their coordinated attempt to chip away, species by species, at the ESA. However, in October, 2020—and in a notable bit of understatement—the USFWS decision stated, “After a thorough review of the best available scientific and commercial information, we find that it is not warranted at this time to delist the DPS of the western yellow-billed cuckoo.”  It would be glorious if we could report that thousands of acres of riparian woodlands had been protected for this population segment. However, in the current political climate that too often disparages environmental concerns—one tiny bullet dodged. At least for now.

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