Guadalupe Murrelet Synthliboramphus hypoleucus Scientific name definitions

The Guadalupe Murrelet (Synthliboramphus hypoleucus) is an obscure species. Plain to the eye, it lives unobtrusively, breeding on only a few specks in the eastern Pacific Ocean and spending the non-breeding period across a vast swath of the North Pacific sparsely populated by both murrelets and humans. In the realm of ornithology, it was relegated to subspecific status and combined with Scripps's Murrelet (Synthliboramphus scrippsi) to form Xantus's Murrelet between the 1930s-2012. The Xantus's Murrelet research that was undertaken was chiefly targeted at the far more accessible Scripps's Murrelet.

We know little of the Guadalupe Murrelet. The estimated 2,651 breeding pairs of Guadalupe Murrelet are almost entirely crammed onto a few islets and rocks off Guadalupe Island and the three islets that constitute Islas San Benito off Baja California's Pacific Coast. More than a century ago, they also bred on the much larger Guadalupe Island but were essentially exterminated by feral cats (Felis catus). Elsewhere, a few pairs recently joined the Scripps's Murrelet colony at San Clemente Island in California's Channel Islands, and a few may also nest on San Martín Island off Baja California. More importantly, an attempt to eliminate cats from Guadalupe Island seems to be succeeding. If successful, a former breeding area would be relatively safe and available again, vastly increasing the number of potential nest sites.

Nest sites are typically naught more than a crevice in a cliff, a well-protected niche under a shrub or a tight spot snuggled among boulders. Nests are unadorned, and if all goes well, two eggs are laid therein. One to two precocious downy chicks hatch about 40 days thereafter, and two days later, the black-and-white fluffballs are lured from their nests into the sea by their parents. At night, the entire family swims off into the ocean headed, literally, for the deep blue sea. Their journey thereafter is a mystery. We know that, from late July into October, most Guadalupe Murrelets inhabit warm waters at least 20 km, and possibly > 90 km off the Pacific Coast of North America from California into Washington, and perhaps, British Columbia. Based on the wee evidence that exists, this species generally winters farther north and farther offshore than does the Scripps's Murrelet. Their return southward probably begins in October, and most or all Guadalupe Murrelets have reconvened near their nesting colonies by December. Upon arriving and throughout the breeding season, congregations of breeding and non-breeding murrelets gather close to these colonies at night, forming vocal congregations, the precise purpose(s) of which remain unclear.

What we assume about Guadalupe Murrelet foraging and diet is almost entirely conjectural, based upon the habits of other Synthliboramphus murrelets: A Guadalupe Murrelet can probably dive up to 25 m in search of its prey, which includes small fish and zooplankton that are captured with the bill; propulsion under water is provided by powerful strokes of the bird's wings as if flying underwater. Visually, the Guadalupe Murrelet certainly resembles its congeners, especially the Craveri's Murrelet (Synthliboramphus craveri) and Scripps's Murrelet. All three species are small alcids approximately 25 cm in length, with a wingspan of about 40 cm and a weight of roughly 160 gm. They are largely black above and white below, with small black bills. Field identification can be challenging, but the Guadalupe Murrelet differs from the other two species in having white that extends up in front of, and often over the eye.