Guadalupe Storm Petrel, Oceanodroma macrodactyla

The Guadalupe Storm Petrel is an extinct species of the Hydrobatidae family. It was a small seabird, almost undistinguishable from its relative, Leach’s Storm Petrel. The only ways to tell them apart was their circannual rhythm and the fact that the Guadalupe Storm Petrel is larger in size and its paler under coverts.

They bred only on Guadalupe Island off Baja, California. The breeding season was set between the local subspecies of Leach’s Storm Petrel, the winder breeding Oceanodroma leucorhoa cheimomnestes and the summer breeding O. l. socorroensis in accordance with Gause’s Law.

The single egg is white with a faint ring of reddish-brown and purple speckles around the dull end and was laid in burrows around 15 inches long. The egg was laid below the Guadalupe Pine- Island Oak fog forest on top of Mount Augusta. By mid-June, almost all young had left the burrows. Although there is not much data on Oceandroma breeding, incubation was presumably 42 days or so, just like other similar sized relatives. Time to fledging must have taken 60 to 75 or 85 days, most likely around 65 days. This would infer that the egg-laying process occurred from early February to March, and that in April-May, unfledged young were present in most active burrows. Just like their relatives, the egg was incubated a few days by either parent, after which the other took over. The relieved parent would take to the ocean to satiate themselves for the next incubation stint. The young were only fed at night, also like other storm-petrels.

There were three species of lice that were found to parasitize the Guadalupe Storm-Petrel: menoponids Longimenopon dominicanum and Austromenopon oceanodromae and the ischnoceran Halipeurus raphanus. The second also occurs on other storm petrels, and the third was also found on the Ashy Storm Petrel.

The disappearance of the storm petrels is mainly from the introduction of cats to the island during the late 19th century. They were still considered “abundant” at the end of the 1906 breeding season. Still, it was noted that “the mortality among these birds from the depredations of the cats that overrun the island is appalling – wings and feathers lie scattered in every direction around the burrows along the top of the pine ridge.”

The last two specimens were presumably collected between May 2nd and May 5th, 1911 and the last evidence of a breeding bird was in 1912. Only the old, vacant burrows and the decayed cadaver of storm petrels that were killed by cats were found in the years thereafter. The Guadalupe Storm Petrel’s breeding grounds were finally surveyed at the right time, from June 4th to June 10th 2000. If the species survived, not only would recently fledged immature birds be present, but also all signs of a recently ended breeding season, such as egg shells and freshly used burrows holding the musky smell of these birds. In the words of Exequiel Ezcurra of the San Diego Natural History Museum, the expedition’s primary researcher, “We searched thoroughly for the Guadalupe Storm Petrel, and failed to find it. Sadly, we are now more ready to admit that the species is indeed extinct. Never, since the 1920s, had so much search effort been devoted to this species. At different times, more than 10 researchers looked for the elusive creature. It simply was not there.”

Official Classification of the IUCN has not been updated yet. In any case, the precautionary approach would most likely require a few years of follow-up surveys, which are possible now that restoration of Guadalupe’s ecosystem is underway.

Image Caption: Guadeloupe Storm-Petrel (Oceanodroma macrodactyla). Credit:
John Gerrard Keulemans/Wikipedia