42

AUDUBON’S SHEARWATER  Puffinus lherminieri 30–33cm, WS 65–74cm.

Caribbean, offshore. Only small black-and-white shearwater to be expected off

Caribbean coast. Likely to be seen as singles, on occasion in small groups; may

associate with feeding flocks of boobies and terns. In light winds, flies low to

water with quick stiff wingbeats and short glides; in stronger winds can wheel

for longer periods but not steeply. Note relatively long tail, dark undertail

coverts. STATUS: Scarce nonbr. migrant, seasonal status poorly known. (Breeds

Caribbean region, ranges in tropical w. Atlantic.)

GALAPAGOS SHEARWATER  Puffinus subalaris 28–31cm, WS 63–70cm.

Pacific, offshore. Only small black-and-white shearwater regular off Pacific coast,

where can occur in sizeable rafts and feeding flocks with Wedge-tailed Shear­

waters, terns, boobies. Flight quick and low to water with fluttery wingbeats,

brief glides; often raises head in flight. Note cleanly demarcated dark/white

border to face and neck sides, narrow whitish spectacles, dark undertail coverts.

Underwing coverts whitish on most birds but dark overall on others (these may

represent cryptic species; study needed). Cf. vagrant Black-vented Shearwater

(Appendix B). STATUS: Irregularly fairly common to common nonbr. migrant,

year-round. (Breeds year-round in Galapagos, ranges in tropical E Pacific.)

CHRISTMAS SHEARWATER  Puffinus nativitatis 33–38cm, WS 83–92cm.

Pacific, offshore. Usually found as singles, sometimes with feeding and rafting

flocks of Wedge-tailed and Galapagos Shearwaters. Flight usually rather low

with quick stiff wingbeats, short glides, but can wheel higher in strong winds.

Note small size, overall rather uniform, dark chocolate-brown plumage, slender

black bill, ample tail; cf. larger but more lightly built dark-morph Wedge-tailed

Shearwater; vagrant Sooty Shearwater (Appendix B). STATUS: Scarce nonbr.

migrant, mainly Mar–Oct. (Tropical Pacific.)

NORTHERN STORM PETRELS (HYDROBATIDAE; 3+ SPECIES) Widespread

family of very small oceanic birds rarely seen from mainland; mostly silent away from breeding

grounds. In Costa Rica, known only from Pacific waters. Ages/sexes similar. Several other species

occur farther offshore (Appendices A–B) but not likely to be found regularly on day trips.

BLACK STORM PETREL  Halocyptena (Hydrobates) melania 21.5–23cm; WS

50–55cm. Very large dark storm petrel with deeply forked tail; often feeds and

rafts with Least Storm Petrel. Flight typically strong and unhurried, with deep

languid wingbeats and easy sailing glides; in strong winds can bank in low arcs.

Note deeply forked tail, big feet (which often dangle), blackish plumage.

Farther offshore, cf. Markham’s and dark-rumped Leach’s Storm Petrels (Appen­

dix B). STATUS: Fairly common to common nonbr. migrant, most numerous

Oct–May; rarely may be seen from shore. (E Pacific.)

LEAST STORM PETREL  Halocyptena (Hydrobates) microsoma 13.5–15cm;

WS 32–36cm. Distinctive, tiny dark storm petrel with rather short, tapered

tail; often feeds and rafts with much larger Black Storm Petrel. Flight typically

quick, with little or no gliding and deep, slightly clipped wingbeats that can

suggest a mini Black Storm Petrel. STATUS: Fairly common to common nonbr.

migrant, most numerous Nov–May; rarely may be seen from shore. (E Pacific.)

PERUVIAN [WEDGE-RUMPED] STORM PETREL  Halocyptena (Hydrobates)

[tethys] kelsalli 14.5–15.5cm; WS 33–37cm. No other white-rumped storm

petrel regular over warmer nearshore waters, but cf. Galapagos, Leach’s, and

Wilson’s Storm Petrels (Appendix B): note big white rump patch (at rest, white

can be all but hidden), flight manner. Often associates with Least and Black

Storm Petrels; flies with deep wingbeats and only brief glides, much like Least.

STATUS: Uncommon to fairly common nonbr. migrant, most numerous May–

Nov. (Tropical E Pacific.)