P27. MOTTLED PETREL Pterodroma inexpectata
Identification Summary Pacific, over cooler waters. A distinctive, medium-sized, fat-bodied, and fairly short-tailed gadfly petrel with high wing-loading. Slightly larger but distinctly heavier-bodied than Cookilaria petrels, with extensively dark belly, broad black carpal-ulnar bar on silvery-white underwing, and frosty gray trailing triangle on upperwing. A strong and fast flier.
Names Pterodroma means “winged runner”; inexpectata apparently refers to the unexpected joy this species brought to its describer. Mottled refers to the scaly aspect to the back (hence the species’ old name of Scaled Petrel).
Status and Distribution Near Threatened. Breeds (Dec–May) s New Zealand, ranges n (mainly May–Oct) to temperate North Pacific. Pacific. Migrates n across cen Pacific (Feb– Jun), occasionally ranging to waters off West Coast (mainly late Feb–Apr), especially in coldwater years (Ainley & Manolis 1979); commoner northward, exceptionally with hundreds off British Columbia in late Apr. Nonbreeding range (May–Oct, mainly Jun–Oct) from s Bering Sea (to 59°N) through Aleutians to Gulf of Alaska, mainly well offshore (Bartle et al. 1993), with southward withdrawal mainly Sep–Oct, although probably some linger later in North Pacific. Irregularly fairly common southbound migrant (late Oct–Dec, mainly mid-Nov to mid-Dec) off West Coast (sometimes hundreds in early Dec, perhaps mainly in cold-water years), occurring farther offshore southward, and usually beyond 370 km by s California; presumably these are immatures migrating later and on a broader front than breeding adults. Beach-washed birds may be found at any season, including mid-summer. Atlantic. Exceptional inland in New York (early Apr 1880).
Similar Species A distinctive species from both above and below. The pattern on the underparts is diagnostic, given the potential exception of another species with an oiled belly, and the pale trailing triangle on the upperwings is also distinctive and can be an arresting feature in some lights. Cookilaria petrels (such as Cook’s) smaller and slimmer-bodied with narrower wings,; their snappier flight is more erratic in moderate to strong winds; their white underparts gleam at long range, and upperwings lack frosty pale trailing triangle. Cook’s also has narrower-looking tail tipped blackish. On the water at moderate range, Cook’s and Mottled can look similar but note white sides and slightly build of Cook’s; also, Mottled usually appears more hooded, or cowled, with contrasting white forehead blaze, whereas Cook’s has more extensive white on throat and foreneck. Murphy’s Petrel has slightly longer, narrower wings and longer tail. Plumage all-dark, but in dull light or strong backlighting Mottled can appear dark overall, even on the underparts unless these are seen at the right angle; note stouter bill and white undertail coverts of Mottled. Habitat and Behavior Pelagic, over cooler waters. Migrating birds may be seen singly or in pulses of birds passing through an area; elsewhere found singly or in small flocks (up to 20 or so birds), at times associating loosely with other seabirds such as Short-tailed Shearwaters. In calm to light winds, sometimes flies with long, low glides (barely above the surface in glassy calm) and bursts of quick flapping; at other times flies high above the horizon, flapping steadily and recalling a jaeger. In moderate to strong winds flies across the wind in high bounding and wheeling arcs with little or no flapping; at other times may wheel relatively low, especially when flying into the wind.
Description Medium-sized, fat-bodied gadfly petrel with a fairly short broad tail and high wing-loading. Ages similar but juveniles (May–Jul at least) average broader scaly white edgings to upperparts and have more extensive whitish on outer rectrices (Marchant & Higgins 1990). Head and upperparts smoky gray with variable blacker eye patch (sometimes quite contrasting); uppertail coverts and tail slightly paler; inner webs of outer rectrices with limited to extensive white freckling. Back in fresh plumage has gray sheen, the feathers with dark shaft streaks, dark subterminal marks, and narrow whitish tips. Blackish M pattern above sets off contrasting paler hindwing panel from secondaries across inner primaries. Throat and underparts white with extensive sooty gray belly patch that sets off bright white undertail coverts; dark from hood sometimes projects down to surround white throat, and chest sometimes scalloped dusky; thus, from above, can appear alldark with white throat patch. Underwings silvery white with thick black carpal-ulnar bar and narrow, dark trailing margins. Bill black, legs and feet bicolored pale pinkish and black. On the water. Sooty gray overall with white throat set off by dark cowl, white undertail coverts and dark sides.
Molt Adult wing molt in North Pacific mainly May–Aug; molt of prebreeders perhaps more protracted (some Nov birds off California completing tail molt; Loomis 1918). PB2 wing molt probably mainly Jan–May in s hemisphere (Murphy & Pennoyer 1952), although some may molt later (Feb/Mar–Jun/Jul) in n hemisphere, paralleling the molt of Sooty Shearwater, another transequatorial migrant.