Leach’s Storm Petrel

Identification

Leach's storm petrel is a diminutive seabird measuring 18–21 cm in length with a 43–48 cm wingspan. It is predominantly black with distinctive field marks: a paler grey-brown bar on the secondary wing coverts, a slightly paler face, and characteristically a white rump, often with a hint of a dark divide down the middle. However, dark-rumped individuals occur on the west coast of North America, becoming increasingly common towards the United States-Mexico border where 90–100% of breeding birds display this variation.

In the Atlantic, Leach's petrel is readily distinguished from European storm petrel and Wilson's storm petrel by its larger size, forked tail, different rump pattern, and distinctive flight behaviour. The species exhibits a fluttering flight and characteristic pattering on the water as it feeds. Separation from band-rumped storm petrels requires careful attention to rump extent and flight pattern, while Pacific identification demands close observation of wingbeats and overall coloration, particularly in dark-rumped populations.

Range & Habitat

Leach's petrel breeds on inaccessible islands in colder northern regions of the North Atlantic and North Pacific Oceans, with a single Southern Hemisphere breeding colony on Dassen Island in South Africa. The largest known colony inhabits Baccalieu Island off eastern Canada, which supported approximately 1.95 million pairs at the last 2013 estimate. Birds nest in colonies close to the sea in well-concealed locations such as rock crevices, shallow burrows, or logs, typically laying a single white egg with a faint purple-spot ring at the large end.

Outside the breeding season, the species is strictly pelagic and difficult to observe from land. Only during storms may individuals be pushed towards headlands. In Europe, autumn offers the best viewing opportunities in Liverpool Bay between north Wales and northwest England, where strong north-westerly gales funnel migrating birds into the bay. The species does not follow ships, distinguishing it from some congeners.

Behaviour & Diet

Leach's petrel is strictly nocturnal at breeding sites, avoiding predation by gulls and skuas and even refraining from landing on clear, moonlit nights. Birds breeding at the Arctic Circle in Norway must delay breeding until autumn to avoid continuous daylight. The species exhibits an unusually long lifespan for its size, averaging 13 years with a maximum recorded age exceeding 38 years, and uniquely shows telomere lengthening with age.

The petrel feeds primarily on plankton including euphausiids, copepods, and parasitic amphipods, supplemented extensively with myctophids (lantern fish) that surface only at night over continental slopes. Individuals forage up to 1000 km from their breeding colony. During incubation and chick-rearing, parents utilize energy-rich lipid reserves. Chicks fledge in late September at reduced weight after reaching nearly double that mass, then migrate to waters associated with the North Equatorial or Benguela Currents. Fall storms occasionally wreck young fledglings on mainland coasts.

Best Time & Places to See It

Leach's petrel presents significant challenges for land-based observation due to its remote island breeding sites and strictly pelagic non-breeding behaviour. The most accessible opportunity in Europe occurs in autumn in Liverpool Bay between north Wales and northwest England, particularly following strong north-westerly gales that funnel migrating birds into coastal waters. Historical observations documented substantial communities on remote Scottish islands including North Rona and Sula Sgeir, with the species first photographed at the nest in 1958 on Eilean Mor in the Flannan Isles.

For dedicated observers, pelagic seabird trips during migration periods offer the best chance of encounter. Storm-driven events may push birds closer to accessible headlands, providing rare land-based sightings. The species' strictly nocturnal behaviour at colonies makes visiting breeding islands particularly challenging and requires specialized access permissions to remote, protected sites.

Photography Tips

Photographing Leach's petrel demands patience and appropriate conditions. The species' pelagic habits necessitate seabird-watching trips or coastal storm-watching during migration periods. The bird's small size, dark plumage, and swift, erratic flight present technical challenges requiring fast shutter speeds and tracking ability. Storm conditions that push birds closer to shore offer enhanced opportunities but demand careful safety precautions.

Key diagnostic features to capture include the white rump pattern (or dark variation on western populations), the pale secondary wing-covert bar, and the characteristic forked tail. The species' fluttering, erratic flight behaviour and water-pattering feeding technique are distinctive photographic subjects. Early morning or evening light during pelagic trips may provide optimal conditions for documenting plumage details and behaviour on the open ocean.