Lifespan, longevity, and ageing
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Maximum longevity: 15 years (wild)
Observations: One banded bird was at least 15 years of age when it was recovered and released (http://bna.birds.cornell.edu/).
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Biology
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Xantus's murrelet is thought to be a monogamous bird which arrives at its island breeding colony around mid-February, about three weeks before it lays its eggs. The female lays two eggs, eight days apart, into a crevice in a cliff, at the back of a small cave, under a boulder, or occasionally, on bare ground beneath thick vegetation (2). Following the laying of the second egg, the male and female will take it in turns to incubate the eggs for the next 34 days. During this time, the eggs are highly vulnerable to predation by deer mice (Peromyscus maniculatus) (2). The chicks are very well-developed on hatching, with limbs that are already 98 percent of the size of adults' (5), and are taken to sea, just one to two days later, by their parents (2). Here, unique to Synthliboramphus, the remainder of the chick's development takes place (6).
In April or May, Xantus's murrelet will move north and west, away from the breeding islands, travelling rather slowly to their wintering areas where they will remain until late November or early December (2). Xantus's murrelet feeds mainly on larval fish, as well as other small prey such as sandeels and crustaceans (2). Diving down to maximum depths of 21 metres and remaining underwater for up to 28 seconds, Xantus's murrelet uses its wings to propel itself through the water to pursue and capture its prey (7). During the breeding season, northern anchovies (Engraulis mordax) comprise a significant part of this murrelet's diet, and thus breeding effort has been noted to be lower when anchovy abundance is low (2).
Conservation
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Since the mid-1990s, introduced mammalian predators have been removed from several of the murrelet's nesting islands (8) (10), such as the eradication of black rats from Anacapa Island, California, with Xantus's murrelet showing encouraging signs of recovery as a result (11). In 2003, fishing was banned within certain areas of the Channel Islands National Marine Sanctuary, which may help reduce noise and light pollution around breeding colonies. Guadalupe Island of Mexico has recently been declared a Biosphere Reserve and the other Mexican islands on which Xantus's murrelet nests are situated either within existing biosphere reserves or in a proposed new biosphere reserve. These measures should hopefully mitigate the negative impacts related to commercial fisheries and tourism (4). In 2005, a special symposium titled “Biology and Conservation of the Xantus's Murrelet” was held, with the aim of increasing awareness of the plight of this species, and to promote the publication of recent findings on its biology and status (10). Such efforts are very encouraging for this threatened seabird, but future conservation actions are still required, including continued efforts to remove the threat of introduced mammals from further critical breeding islands (4) (8).
Description
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This small marine bird belongs to the genus Synthliboramphus, a group of seabirds remarkable for the fact that they are the only seabirds which rear their young entirely at sea (3). Xantus's murrelet has striking black and white plumage: black on the upperparts, sometimes tinted faintly with grey as the feathers become worn, and snowy white on the underside. The flanks may be white or mottled grey and white, the legs are bluish-grey, and the feet bear black claws (2). Two subspecies of Xantus's murrelet are recognised: Synthliboramphus hypoleucus hypoleucus and Synthliboramphus hypoleucus scrippsi. The former can be recognised by the prominent white crescents above and below the eye, while the white patterning on the face of S. h. scrippsi is very indistinct (2) (4). Female Xantus's murrelets are usually larger than the males, while juveniles may be distinguished by the scattered dark barring along the flanks (2). This seabird calls with a shrill whistle (4).
Habitat
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Breeding on steep cliffs above the sea, as well as on slopes and canyons (2), Xantus's murrelet selects areas where there is a sparse cover of shrubs and herbs (4). During winter, this bird can be found offshore, in the warm waters of the California Current (2).
Range
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Xantus's murrelet breeds off the coast of southern California, USA, and Baja California, Mexico (4). The two subspecies have different breeding ranges, overlapping only on the San Benito Islands off Baja California. S. h. scrippsi breeds on the southern California Channel Islands and on islands off the west coast of Baja California, while S. h. hypoleucus breeds only off Baja California, on the three San Benito Islands and on two rocks offshore of Guadalupe Island. Previously, more breeding colonies may have existed on other islands, before they were destroyed by invasive animals (4). Outside of the breeding season, this small seabird ranges from the southern tip of Baja California, north to British Columbia, Canada (2).
Status
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Classified as Vulnerable (VU) on the IUCN Red List (1).
Threats
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One of the most significant threats to this Vulnerable bird is the impact of invasive mammals, including feral cats, black rats and house mice, which prey on the eggs, young, and occasionally adults of Xantus's murrelet (4) (8) (9). The extinction of some breeding colonies in the past as a result of invasive mammals demonstrates the devastating affect that they can have on this species (4).
In addition to the threats of invasive species, Xantus's murrelet could be affected by oil spills, drowning in fishing gear, pollution, and disturbance of nesting sites (4). In the future, changes in sea temperature caused by global climate change may also have a detrimental impact on this species if it alters the availability of prey, such as the northern anchovy (4).
Guadalupe murrelet
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The Guadalupe murrelet (Synthliboramphus hypoleucus) or Xantus's murrelet is a small seabird found in the California Current system in the Pacific Ocean. This auk breeds on islands off California and Mexico. It is threatened by predators introduced to its breeding colonies and by oil spills.[2][3]
This species together with the Scripps's murrelet were considered conspecific and were classified under S. hypoleucus; known collectively as Xantus's murrelet until 2012. Enough evidence was collected to consider both species distinct based on a lack of evidence of interbreeding where the two species nest together on the San Benito Islands, differences in facial pattern and bill shape, vocalizations and genetics.[4][5][6]
Description and range
This species is a small black and white auk with a small head and thin sharp bill. It resembles the closely related Scripps's and Craveri's murrelet, with which it shares the distinction of being the most southerly living of all the auk species. It breeds from Guadalupe Island south to the San Benito Islands. After the breeding season it disperses locally at sea northward up to southern California in the United States.
Behavior
Guadalupe murrelet feeds far out at sea, often in association with large pelagic predatory fish like tuna, on larval fish like anchovies, sardines and Sebastes rockfish. Like all auks it is a wing-propelled diver, chasing down prey under the water with powerful wingbeats. There is some speculation that it may feed cooperatively in pairs, as it is almost always observed in pairs, even during the non-breeding season. It flies well, and can take off without taxiing.
It nests in small crevices, caves and under dense bushes on arid islands in loose scattered colonies. It returns to the colony only at night, laying two eggs which are incubated for about a month. Like other synthliboramphine murrelets (e.g. the ancient murrelet) the chicks are highly precocial, leaving the nest within two days of hatching and running actively towards the sea, where the parents call to them. Once at sea the family swims to offshore waters.
Little is known about the time at sea due to difficulties in studying them.
Status and conservation
By the end of the 20th century, the Xantus's murrelet complex was considered to be among the most endangered group of auk.[7] This has changed since, but not because the present species' status has improved, but because other auks have become rarer.
Guadalupe murrelet is mainly threatened by oil spills, as much of its population lives near the busy shipping lanes connecting Los Angeles to other ports. Because a large part of its small population nests in such a small area a single catastrophic oil spill could have far reaching implications. It is also threatened by introduced species such as rats and feral cats; this threat has been lessened lately by efforts to restore its habitat by removing introduced predators.
References
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^ BirdLife International (2018). "Synthliboramphus hypoleucus". IUCN Red List of Threatened Species. 2018: e.T62101215A132673655. doi:10.2305/IUCN.UK.2018-2.RLTS.T62101215A132673655.en. Retrieved 13 November 2021.
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^ Jones, Holly P.; Williamhenry, R.; Howald, Gregg R.; Tershy, Bernie R.; Croll, Donald A. (December 2005). "Predation of artificial Xantus's murrelet (Synthliboramphus hypoleucus scrippsi) nests before and after black rat (Rattus rattus) eradication". Environmental Conservation. 32 (4): 320–325. doi:10.1017/S0376892906002608. ISSN 1469-4387. S2CID 49360219.
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^ Nettleship, David N.; Kirwan, Guy M. (2020). "Guadalupe Murrelet (Synthliboramphus hypoleucus), version 1.0". Birds of the World. doi:10.2173/bow.xanmur1.01. S2CID 216216779.
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^ Birt, T. P.; H.R. Carter; D.L. Whitworth; A. McDonald; S.H. Newman; F. Gress; E. Palacios; J.S. Koepke & V.L. Friesen (2012). "Rangewide population genetic structure of Xantus's Murrelet, (S. hypoleucus)". Auk. 129: 44–55. doi:10.1525/auk.2011.11011. S2CID 86799974.
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^ Jehl, J. R. Jr.; S.I. Bond (1975). "Morphological variation and species limits in murrelets of the genus Endomychura" (PDF). Transactions of the San Diego Society of Natural History. 18: 9–24. doi:10.5962/bhl.part.15542.
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^ Keitt, B.S. (2005). "Status of Xantus's Murrelet and its nesting habitat in Baja California, Mexico" (PDF). Marine Ornithology. 33: 105–114.
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^ IUCN Redlist (1988, 1994, 2000)
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Guadalupe murrelet: Brief Summary
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The Guadalupe murrelet (Synthliboramphus hypoleucus) or Xantus's murrelet is a small seabird found in the California Current system in the Pacific Ocean. This auk breeds on islands off California and Mexico. It is threatened by predators introduced to its breeding colonies and by oil spills.
This species together with the Scripps's murrelet were considered conspecific and were classified under S. hypoleucus; known collectively as Xantus's murrelet until 2012. Enough evidence was collected to consider both species distinct based on a lack of evidence of interbreeding where the two species nest together on the San Benito Islands, differences in facial pattern and bill shape, vocalizations and genetics.
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