Justification of Red List category
This species has a small breeding population and the presence of introduced predators on most known and potential breeding islands, along with other associated threats, suggests that numbers are likely to be declining. It consequently qualifies as Vulnerable.
Partners in Flight (2019) estimate the population of Synthliboramphus craveri to total 8,000 mature individuals, or 12,000 individuals. Such estimates are marginally less than Gaston and Jones's (1998) older estimate of 15,000-20,000 birds and Pitman et al.'s (1995) at-sea survey estimate of c.22,000 birds, as would be expected given the moderate ongoing population declines.
Moderate ongoing declines are suspected owing to the various threats acting throughout the species's population.
Synthliboramphus craveri is endemic to Mexico, scattered throughout the Gulf of California and the Pacific coast of the Baja California Peninsula (Everett and Anderson 1991). In the Gulf of California, it breeds on islands: Partida, Rasa, Tiburón, Ángel de la Guarda, Mejía, Salsipuedes, Las Ánimas, Alcatraz, San Jorge, San Luis, San Esteban, Estanque, Dátil, Cholludo, San Pedro Mártir, San Pedro Nolasco, San Francisco, Espíritu Santo and San Ildefonso (Everett and Anderson 1991, Hurley and Blinick 2011, Velarde et al. 2011, Bowen 2013, GECI 2019a). On the Pacific coast, it breeds on islands: San Martín, San Benito, Cedros, Natividad, Asunción and San Roque (Velarde et al. 2011, Whitworth et al. 2018, GECI 2019a, Bedolla-Guzmán et al. 2019b). 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). Recent ground and at-sea surveys around Midriff islands and Baja California Pacific islands indicated the presence of less than 1,000 individuals (F. Méndez-Sánchez in litt. 2020). 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).
One to 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 from just above the high-tide mark to several dozen meters up sea-facing slopes (DeWeese and Anderson 1976, Gaston and Jones 1998, Velarde et al. 2011). Mean clutch sizes are 1.4 (n=23) (F. Méndez-Sánchez in litt. 2020). Colony size can vary from a few nests to several dozens (2-52 nests in the Gulf of California, 1-7 nests in the Pacific) as well as at-sea congregations (1-87 individuals in the Gulf of California, 9-130 individuals in the Pacific) (Whithworth et al. 2017, F. Méndez-Sánchez in litt. 2020). In the Gulf of California, eggs are laid in early February-March and chicks hatch around March-April (DeWeese and Anderson 1976, Hurley and Blinick, 2011), whereas in the Pacific eggs are laid in early April and chicks hatch in May (Méndez-Sánchez in litt. 2020). Hatching success is high both in the Gulf of California (90%, n=8) and in the Pacific (85%, n=10), with overall 1.2 chicks laid by each breeding pair, although numbers may vary inter-anually (F. Méndez-Sánchez in litt. 2020). 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, but also small squid and crustaceans (DeWeese and Anderson 1976).
Invasive alien species are the main threat to Craveri’s Murrelet population on their nesting sites (DeWeese Aguirre-Muñoz et al. 2018, GECI 2019a). Historically, 70% of its breeding sites were threatened by non-native predators such as cats, rats, mice which caused local extinctions (Velarde et al. 2011, Aguirre-Muñoz et al. 2018). Colonies were extirpated from San Pedro Mártir, San Jorge, Rasa, Espíritu Santo, Natividad, Asunción and San Roque islands (Velarde et al. 2011, Bedolla-Guzmán et al. 2019a). Targeted eradication efforts from 1995 to 2017 have removed invasive mammals from the majority of islands within the species' range, with the exception of the biggest islands such as Cedros, Ángel de la Guarda and San Esteban that still host these predators (Aguirre-Muñoz et al. 2018). However, the risk of reintroduction is high on inhabited islands that are now pest-free due to continuous movements from the continent by fishermen, tourists and researchers (Bedolla-Guzman et al. 2019b).
Oil spills from grounding, ship collisions or sinking of ships, as well as pipelines near the coast and pollution from offshore wells could threaten a large percentage of breeding adults (Velarde and Anderson 1994). On the Pacific coasts of California, Washington, and British Columbia, where the species is distributed during the non-breeding season, large oil spills have occurred with serious ecological implications (the pipeline failure in Refugio State Beach, California, in 2015; Exxon Valdez oil spill due to a collision with the Bligh Reef, in Prince William Sound, Alaska, in 1989). 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.
During its breeding season, Craveri's Murrelet acquires nocturnal habits that allow it to evade certain predators (Montevecchi 2006). However, there are populations of birds that have the potential to become abundant by anthropogenic facilitation and this process must be monitored, as is the case for Western Gull (Larus occidentalis), Yellow-footed Gull (Larus livens) and Common Raven (Corvus corax). Other predator native species that cohabitate with Craveri's Murrelet on islands are Peregrine Falcon (Falco peregrinus), Burrowing Owl (Athene cunicularia) and Barn Owl (Tyto alba). The impact of these predators on the demography of Craveri's Murrelet has not yet been evaluated (GECI, 2019). Light pollution at-sea could represent another potential threat for the species, especially those caused by squid fishery that can extend from the Gulf of California to the western coast of the Baja California Peninsula (SAGARPA 2014). This type of light pollution could prevent nocturnal seabirds from approaching their breeding sites, or being attracted to and getting trapped in fishing nets, or colliding with the boats. Plastic ingestion has been recorded in murrelets (Avery-Gomm et al. 2013), however, there is still no evidence of plastic intake or damage by plastics in Craveri's Murrelet, thus, this threat also needs more exploration.
Conservation Actions Underway
In Mexico is listed as Endangered by the Mexican Official Standard, NOM-059-SEMARNAT-2010 (DOF 2010) and all breeding sites are part of Natural Protected Areas. In the Gulf of California, all the terrestrial parts of the islands are part of the Flora and Fauna Protection Area "Islas del Golfo de California" (SEMARNAT 2000), also inscribed on the UNESCO's World Natural Heritage list, and there are several marine protected areas (CONANP 2007, SEMARNAT 2014a, 2014b). San Pedro Mártir Biosphere Reserve and the National Park Zona Marina del Archipiélago Espíritu Santo were recently included in the IUCN Green List. Islands along the Pacific coast of the Baja California Peninsula are protected by El Vizcaíno Biosphere Reserve (INE 2000) and the Baja California Pacific Islands Biosphere Reserve (DOF 2016). Introduced mammals (black rat, house mouse, deer mouse, rabbit, cat and goat) were eradicated from a number of islands that are current, past or potential breeding sites. In the Gulf of California, on San Jorge (2000-2002), Mejía (1999-2001), Estanque (1999), Rasa (1995-1996), San Pedro Mártir (2007), San Francisquito (1999-2000) and Espíritu Santo (2015-2017). In the Pacific, on San Martín (1999), San Benito (1999-2013), Natividad (1997-2001), San Roque (1999) and Asunción (1999) (Tershy et al. 2002, Aguirre-Muñoz et al. 2018). Feral goat eradication on Espíritu Santo is in its final stages (F. Méndez-Sánchez in litt. 2020). Recolonization of extirpated colonies after eradications have been reported on San Pedro Mártir, San Jorge, Rasa, Natividad, Asunción and San Roque (DeWeese and Anderson 1976, Velarde et al. 2011, Aguirre-Muñoz et al. 2018, GECI, 2019a, Bedolla-Guzmán et al. 2019a, b). A conservation action plan for the species (GECI, 2019a) and an island biosecurity plan for several islands have been developed (GECI 2017, 2018, 2019b) and are now implemented by the National Commission of Natural Protected Areas in the Midriff islands (J. Zatarain-González in litt. 2020). Continuous detection monitoring of invasive mammal species is implemented on the Midriff islands (Bedolla Guzmán et al. 2017, 2019a, J. Zatarain-González in litt. 2020). Other conservation measures include continued environmental education with local communities and increased enforcement of existing regulations (J. Zatarain-González in litt. 2020). Whilst human use of the islands is increasing, it is widely monitored and under constant surveillance and regulation (J. Zatarain-González in litt. 2020).
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
Fjagesund, T., Everest, J., Martin, R.
Aguilar-Vargas, A., Anderson, D., Aztorga-Ornelas, A., Bedolla-Guzmán, Y., Benstead, P., Fabila-Blanco, A., Félix-Lizárraga, M., Gilroy, J., Miller, E., Méndez Sánchez, F., Tershy, B., Verlarde, E. & Zatarain, J.
BirdLife International (2023) Species factsheet: Synthliboramphus craveri. Downloaded from http://datazone.birdlife.org/species/factsheet/craveris-murrelet-synthliboramphus-craveri on 01/12/2023.
Recommended citation for factsheets for more than one species: BirdLife International (2023) IUCN Red List for birds. Downloaded from http://datazone.birdlife.org on 01/12/2023.