Justification of Red List Category
This species has a small breeding range and population which nests at a small number of known locations. The presence of introduced predators on most known and potential breeding islands suggests that numbers are likely to be declining significantly. It consequently qualifies as Vulnerable.
The population is estimated to number 9,000-15,000 individuals, roughly equating to 6,000-10,000 mature individuals.
Population declines are suspected owing to the various threats acting on all populations.
Synthliboramphus craveri has an estimated c.5,000 breeding pairs, scattered throughout the Gulf of California, Mexico (Everett and Anderson 1991). It breeds on Islas Partida, Tiburón, San Jorge, San Esteban, Estanque, San Pedro Mártir, San Pedro Nolasco, San Francisco, Espíritu Santo and San Ildefonso, and possibly on the Pacific coast of Baja California, north to Islas San Benitos (DeWeese and Anderson 1976, Everett and Anderson 1991, Velarde and Anderson 1994, E. Velarde in litt. 1998). The population, with pre-breeders, is probably 15,000-20,000 birds (Gaston and Jones 1998), which is similar to an at-sea survey estimate of c.22,000 birds (Pitman et al. 1995). It winters in the Gulf of California and along coasts to south California, USA, and Sonora, Mexico, and possibly Guatemala (DeWeese and Anderson 1976, Tershy et al. 1993).
Two eggs are usually laid on bare rock or soft substrate at the end of a rock-cavity or crevice, but also in ground-burrows, under dense shrubs and boulders (DeWeese and Anderson 1976, Gaston and Jones 1998). Nesting success varies from 12-79%, but chick survival during the first month at sea is only 30-35% (DeWeese and Anderson 1976). It feeds mainly on larval fish, especially rockfish Sebastes, herring (Clupeidae) and lanternfish Benthosema panamense (DeWeese and Anderson 1976).
Cats and rats are probably the greatest threat, presumably predating both adults and nests on several breeding islands (DeWeese and Anderson 1976). Deer mice may also pose a threat on some islands. Oil spills from the tanker lane stretching from the Gulf of California to Puerto Libertad could threaten a large percentage of breeding adults. Pollution from offshore oil-wells or the Los Angeles oil-tanker lane could also affect non-breeding adults in the south California Bight (Velarde and Anderson 1994). Further threats are drowning in drift gill-nets, nest-site disturbance and possibly organochlorine pollution (Velarde and Anderson 1994).
Conservation Actions Underway
A management plan and implementation strategy for the Gulf of California Special Biosphere Reserve were detailed in 1994 (Velarde and Anderson 1994), and work began in 1999 (D. W. Anderson in litt. 1999). Introduced mammals have been eradicated from a number of islands that are current, past or potential breeding sites (B. Tershy in litt. 1999, Tershy et al. 2002, B. Tershy in litt. 2007, Aguire et al. in press). Instructive signs have been placed on many of the islands and there is a general move towards increasing enforcement of existing regulations. At the same time, human use of the islands is increasing, much of it unregulated (B. Tershy in litt. 1999). Other measures include the development of management plans for all known breeding islands, environmental education, the erection of warning signposts on islands and increased enforcement of existing regulations (B. Tershy in litt. 1999).
25 cm. Small, black-and-white alcid. Black upperparts, white below. Black partial collar extending on to sides of breast. Black on head extends just under bill. Partial white eye-ring. Long slim bill. Dusky grey underwing linings. Similar spp. Xantus's Murrelet S. hypoleucus lacks partial breast-band and black extending under bill, and has white underwing linings and shortish, stout bill. Voice Shrill whistle, sometimes given as series.
Text account compilers
Benstead, P., Gilroy, J.
Verlarde, E., Anderson, D., Tershy, B.
BirdLife International (2018) Species factsheet: Synthliboramphus craveri. Downloaded from http://www.birdlife.org on 23/07/2018. Recommended citation for factsheets for more than one species: BirdLife International (2018) IUCN Red List for birds. Downloaded from http://www.birdlife.org on 23/07/2018.