Leach's Storm-Petrel Identification Guide
A small, dark, fork-tailed seabird of the open ocean that nests in burrows on remote islands and is best identified at sea by its erratic, bounding flight and pale rump.
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Key Field Marks
- Size & shape: A small storm-petrel about 19–22 cm (7.5–8.7 in) long with a wingspan around 45–48 cm (18–19 in); long, angled wings, a forked tail, and a moth-like, buoyant flight.
- Plumage: Overall sooty-brown to blackish body with a paler brownish-gray diagonal bar across the upperwing coverts; the rump is white but often divided by a faint dark central line (variable, sometimes appearing all-dark in some populations/morphs), unlike the solid white rump of many other storm-petrels.
- Tail: Distinctly forked tail, visible in good views and a key difference from the square-tailed Wilson's Storm-Petrel.
- Flight: Erratic, bounding, and buoyant flight with deep, floppy wingbeats and frequent changes of direction and speed, often veering and zigzagging low over the water — quite different from the fluttering, direct flight of Wilson's Storm-Petrel.
- Behavior: Almost entirely pelagic outside the breeding season, feeding on small fish, squid, and plankton picked from the surface; nests colonially in burrows on offshore islands, visiting colonies only at night.
Separating It From Similar Species
- Wilson's Storm-Petrel: Has a square (not forked) tail, direct fluttering flight with feet often visible trailing beyond the tail and sometimes pattering on the water, and a solidly white rump wrapping around onto the undertail.
- Band-rumped Storm-Petrel: Similar dark plumage and forked tail but flight is more direct and less erratic than Leach's, with a broader, more solidly white rump band and different wingbeat pattern.
- Ashy Storm-Petrel and other dark-rumped storm-petrels: Lack any white rump patch at all, appearing uniformly dark, unlike Leach's variable but usually at least partly white rump.
Where & When to See It
- Range: Breeds on remote islands in the North Atlantic and North Pacific, including islands off Newfoundland, Maine, Alaska, and British Columbia; winters widely at sea in tropical and subtropical waters of the Atlantic and Pacific.
- Habitat: Entirely pelagic away from breeding sites, favoring deep offshore waters; nests in burrows dug into soil on grassy or forested offshore islands free of mammalian predators.
- Season: Present at breeding colonies from spring through early fall, visiting nesting burrows only after dark to avoid predators; otherwise ranges far offshore, best seen on dedicated pelagic boat trips.
Voice & Song Cues
- Silent at sea; at nesting colonies at night gives an eerie, chattering, purring call often described as a series of chuckling notes ending in a sharp "chi-ka" or "tuk-a-tuk," typically heard from within or near the burrow.
Frequently asked questions
How do I tell Leach's Storm-Petrel from Wilson's Storm-Petrel at sea?
Leach's has a forked tail and erratic, bounding flight with deep wingbeats, while Wilson's has a square tail, more direct fluttering flight, and often trails its feet beyond the tail or patters them on the water surface.
Does Leach's Storm-Petrel always have a white rump?
Most individuals show a white rump, though it is often divided by a thin dark central line, and some populations or individuals can show reduced or nearly all-dark rumps, so rump pattern alone should be combined with tail shape and flight style.
Where can I see a Leach's Storm-Petrel?
Since it is almost entirely pelagic away from its nesting islands, the best way to see one is on an organized boat trip well offshore; at breeding colonies it only visits its burrow after dark, making onshore observation very difficult.
What does Leach's Storm-Petrel sound like at its colony?
At night near nesting burrows it gives an eerie, chattering, purring call that often ends in a sharper 'chi-ka' note, audible from within the burrow or as birds fly in after dark.
Why is Leach's Storm-Petrel's flight described as erratic?
It flies with deep, floppy wingbeats and frequent, unpredictable changes in direction and speed, giving a bounding, moth-like flight pattern that differs noticeably from the steadier flight of many other storm-petrels.