About Oceanodroma leucorhoa (Vieillot, 1818)
Scientific name: Oceanodroma leucorhoa (Vieillot, 1818)
Description: Leach's petrel is a small bird, measuring 18–21 cm in length with a 43–48 cm wingspan. Like many other storm petrels, it has all-black plumage overall. Exceptions include a paler grey-brown bar on the secondary wing coverts, a slightly paler face, and usually a white rump with a faint dark stripe running down the middle. However, dark-rumped individuals exist along the west coast of North America. Dark-rumped birds are very rare north of southern California, but the proportion of this type increases suddenly at the United States-Mexico border, where 90-100% of breeding Leach's petrels are dark-rumped.
In the Atlantic region, Leach's petrel can be easily told apart from the European storm petrel and Wilson's storm petrel by its larger size, forked tail, different rump pattern, and flight behaviour. But separating it from band-rumped storm petrels is difficult, and identification relies on features like the extent of white on the rump and flight pattern. Identification is even more challenging in the Pacific; the dark-rumped form can be confused with at least three other all-dark storm petrel species, so identification requires close attention to wingbeats and overall colour.
Leach's petrel has a fluttering flight, and it patters on the water surface to pick up planktonic food. Like most petrels, it can only walk with a short shuffle when moving to its burrow.
Distribution and habitat: Leach's petrel is strictly pelagic when it is not breeding. Combined with its use of remote islands as breeding sites, this makes the species difficult to observe from land. It may only be pushed into headlands during storms. Unlike the European storm petrel, it does not follow ships.
In Europe, the best opportunity to see Leach's petrel is in autumn in Liverpool Bay, which lies between north Wales and northwest England. Strong north-westerly gales can funnel migrating Leach's petrels into this bay. British ornithologists Robert Atkinson and John Ainslie observed Leach's petrel communities on the remote Scottish island of North Rona between 16 July and 12 August 1936, and on Sula Sgeir between 3 and 4 August 1939. The first photograph of this species at the nest was taken in 1958 by Jo Moran, on Eilean Mor, one of the Flannan Isles off the west coast of Scotland's Outer Hebrides.
Ecology: Leach's petrel has an unusually long lifespan for such a small bird, with an average lifespan of 13 years, and a maximum recorded lifespan of over 38 years (a bird ringed between 1979 and 1982 was recaptured healthy in 2019). In 2003, researchers found that Leach's petrel's telomeres lengthen with age, which was the only known confirmed example of this phenomenon at that time. This phenomenon likely also occurs in other members of the Procellariiformes, an order whose members all have relatively long lifespans for their body size.
Leach's petrel feeds primarily on plankton, including euphausiids, copepods, and a type of amphipod that parasitizes the gonadal pouches of jellyfish. It also feeds heavily on myctophids (lantern fish), which only come to the surface at night in waters over the continental slope. Individual Leach's petrels have been observed feeding as far as 1000 km away from their breeding colony.
Breeding individuals store energy-rich lipids in a sac located in front of their stomach. This stored energy is used to sustain the bird while it incubates its single egg, or to feed its chick. Like many other Procellariiformes, Leach's petrel can also use this stored material as a defense mechanism when caught by a predator. Some evidence indicates that parent birds feed their chicks different prey species than the ones they consume themselves. Parent birds also accidentally feed plastic debris to their chicks, after mistaking the floating plastic for food on the ocean surface.
Chicks reach a pre-fledging weight that is almost double the weight they have when they actually fledge from the burrow in late September. During migration, Leach's petrels travel to waters associated with the North Equatorial Current, or to waters associated with the Benguela Current. Fall storms can push these newly fledged young individuals onto the mainland, causing them to wreck.
