Cuckoos are known worldwide for their bizarre haunts and habits, and the Yellow-billed Cuckoo is no exception. Furtive, retiring, and watchful by nature, this species' presence may be first revealed by its hollow, wooden call: ka-ka-ka-ka- kow-kow-kow-kow-kowlp-kowlp-kowlp. It has been dubbed the “Raincrow” because of its apparent tendency to call more frequently on cloudy days, although its proficiency as predictor of weather has never been demonstrated.
The summer distribution of the Yellow-billed Cuckoo ranges throughout much of the United States, southeastern Canada, the Greater Antilles, and Mexico, but range boundaries have been confused by recurrent observations of nonbreeding individuals away from breeding sites. Vagrants are not infrequent on Atlantic shores and prairies in Canada, and occasionally wander as far as Alaska and Western Europe. Although generally considered a nearctic-neotropical migrant, some southern populations may prove to be sedentary. Furthermore, immature cuckoos collected in South America in summer suggest isolated breeding sites at tropical latitudes.
Like other cuckoos, the breeding behavior of the Yellow-billed Cuckoo is peculiar. The onset of breeding is apparently correlated with an abundant local food supply. Once initiated, the breeding cycle is extremely rapid, and requires only 17 days from egg-laying to fledging of young. Bursting feather sheaths allow nestlings to become fully feathered within two hours. In addition, the Yellow-billed Cuckoo and its congener, the Black-billed Cuckoo (Coccyzus erythropthalmus), are the only known facultative, interspecific brood parasites among altricial birds. At least 11 passerine species have been used as hosts, most frequently the American Robin (Turdus migratorius), Gray Catbird (Dumetella carolinensis), and Wood Thrush (Hylocichla mustelina). Although the production of extra eggs has been shown, in some cases, to coincide with periodic outbreaks of caterpillars and cicadas, behavioral and physiological mechanisms controlling parasitism remain obscure. The Yellow-billed Cuckoo has also been observed to breed cooperatively in California with at least three or four adults tending a single nest, and in Arizona, facultative serial polyandry has been reported.
Unfortunately, the future of the Yellow-billed Cuckoo is uncertain. Populations are declining precipitously throughout its distribution. Western populations have suffered severe range contractions during the twentieth century, and are already extirpated from British Columbia, Washington, and Oregon. In California, this cuckoo once numbered more than 15,000 pairs, but the population has been reduced to about 40 pairs in less than 100 years, owing primarily to the destruction and degradation of preferred riparian habitat.
Until recently, the critically imperiled western population received no federal protection due largely to controversy surrounding the validity of its subspecies status. After almost 30 years of petitioning, however, the western subspecies of Yellow-billed Cuckoo was successfully deemed a distinct population segment and was granted protection as threatened under the Endangered Species Act in October 2014. A proposed rule to designate critical riparian habitat under the Act is pending. Immediate conservation intervention is essential to ensure that the "Raincrow" continues to be heard calling among western cottonwoods.
Some aspects of Yellow-billed Cuckoo life history have been studied, although few are well known. Feeding and nesting behavior is described by Hamilton and Hamilton ( Hamilton III and Hamilton 1965 ), Laymon ( Laymon 1980 ), Halterman (1991, 2009), and Wilson (1999a), with detailed observations of single nests reported by Preble ( Preble 1957 ) and Potter ( Potter 1980 ). In addition, some anomalous breeding behaviors have been recorded (e.g., Nolan and Thompson 1975 , Fleischer et al. 1985b , Laymon et al. 1997, Laymon 1998, Halterman 2009). The distribution and status of western populations has been quantified by Gaines and Laymon ( Gaines and Laymon 1984 ), Howe ( Howe 1986 ), Groschupf ( Groschupf 1987 ), and Laymon and Halterman ( Laymon and Halterman 1987 ). In addition, extensive study of habitat use, population estimates, and human-caused threats in western populations have been undertaken. See USFWS 2013, 2014a, 2014b, and references therein.