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). The species winters in the Gulf of California and along the coast to south California (U.S.A.), Sonora (Mexico) and possibly Guatemala (DeWeese and Anderson 1976, Tershy et al. 1993).
Two eggs are 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). The species feeds mainly on larval fish, especially rockfish Sebastes sp., herring (Clupeidae) and lanternfish Benthosema panamense (DeWeese and Anderson 1976).
Introduced cats Felis catus and House Rats Rattus rattus depredate both nests and adult birds on several islands, and pose a serious threat to the species (DeWeese and Anderson 1976). Local extinctions have been linked to the presence of non-native predators (Velarde et al. 2011); the species was previously recorded on San Jorge Islands (DeWeese and Anderson 1976) but was likely extirpated due to rat predation, as has been observed elsewhere in the region for the same genus (McChesney and Tershy 1998, Donlan et al. 2003). Targeted eradication efforts have removed invasive mammals from the majority of islands within the species's range, with the exception of Cedros, which is thought to hold up to 150 pairs of Craveri's Murrelet and still hosts both cats and rats (Carter et al. 2011).
Oil spills from the tanker lane stretching from the Gulf of California to Puerto Libertad could threaten a large percentage of breeding adults, as well as pollution from offshore oil-wells (Velarde and Anderson 1994). Agriculture and forestry represent another source of pollutants. In the Yaqui Valley, fertilizer application rates are extremely high (250 kg of nitrogen per ha) and these materials are quickly washed out by surface water run-off from irrigation. Berman et al. (2005) used satellite imagery to demonstrate the relation of irrigation activity and run-off intensity to meso-scale phytoplankton blooms. Further, they suggested that up to 22% of the annual chlorophyll variability in the Gulf of California is related to the nitrogen run-off from the Yaqui Valley (Lluch-Cota et al. 2007), which could cause direct mortality of murrelets and also degrade the ecosystem, potentially reducing prey availability. The species if thought to be at risk from incidental capture in small- and large-scale fisheries, though the impact has not been quantified.
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, Aguirre-Muñoz et al. 2008). 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 conservation 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., Fjagesund, T., Martin, R., Miller, E., Gilroy, J.
Tershy, B., Anderson, D., Verlarde, E.
BirdLife International (2020) Species factsheet: Synthliboramphus craveri. Downloaded from http://www.birdlife.org on 26/02/2020. Recommended citation for factsheets for more than one species: BirdLife International (2020) IUCN Red List for birds. Downloaded from http://www.birdlife.org on 26/02/2020.