Swinhoe's Storm-Petrel | Hydrobates monorhis

Voice

Silent at sea. At the colonies at night a fast, rattling chuk-chuk-chuk-churrr, similar to Leach's Storm-Petrel, and purring from the burrows.

Identification

Medium-sized, uniformly dark chocolate-brown, including the rump, with a clearly forked tail that often looks square at a distance. A pale brown bar runs across the upperwing coverts; the shafts at the base of the outer primaries are white, giving a small pale spot at close range. Wings long and angled at the wrist. Flight fast and erratic, with sudden swerves and short glides, very like Leach's Storm-Petrel.

Confusion species

Matsudaira's Storm-Petrel (Hydrobates matsudairae), a rare vagrant to the Gulf of Eilat, is larger, with a slower flight and a bigger, more obvious white patch on the primaries. Wilson's Storm-Petrel (Oceanites oceanicus), much commoner in the Arabian Sea in summer, has a bright white rump, a square tail and feet projecting beyond the tail. Leach's Storm-Petrel (Hydrobates leucorhous) always has a white rump in the Atlantic population. Bulwer's Petrel (Bulweria bulwerii) and Jouanin's Petrel (Bulweria fallax) are also all dark but much larger, with a long wedge-shaped tail and a calm, shearwater-like flight.

Habitat

Open sea, both far out on the ocean and over the continental shelf and in deep gulfs and bays; sometimes follows fishing boats. In the Arabian Sea mainly in the cool, productive upwelling zone off southern Oman that develops during and after the south-west monsoon.

Range and movements

Oman: regular in the Arabian Sea, most often in October and November on boat trips off Muscat, Ras al-Hadd, Masirah and Dhofar, but also from May to September; scarcer in the Gulf of Oman. United Arab Emirates: rare but probably regular off the east coast at Fujairah, mainly mid-August to mid-September, usually more than thirty kilometres offshore. Yemen: records in the Gulf of Aden and around Socotra in October. Israel: more than ten records in the Gulf of Eilat since the 1990s in almost all months, concentrated in June to September; probably present almost year-round in the Gulf of Aqaba, and so to be expected off Jordan and Egyptian Sinai too. Egypt: one record in the Red Sea in August 2023. The Saudi and Sudanese Red Sea is hardly searched. Elsewhere it breeds on islands off Korea, China, Japan and the Russian Far East, the great majority on a single islet off Korea; it winters in the northern Indian Ocean from Sri Lanka and the Maldives to the Arabian Sea. A very rare vagrant to the Mediterranean and the Atlantic.

• Summer visitor (c. Oct–Mar)
• Passage (Mar–Apr, Oct–Nov)
• dark = core range, pale = thinly spread

How and when to look

A pelagic trip out of Muscat or a Dhofar harbour in October or November gives the best chance, ideally with fish offal to draw the birds to the boat. In Israel they are seen in September from the viewpoint on the south coast of Eilat and on organised boat trips; look for the dark rump, the forked tail and the white primary shafts.

Conservation status

Near Threatened. The world population is estimated at at least 130,000 pairs, most of which breed on one small island; introduced rats and cats and disturbance could quickly do great damage there, and some colonies are reported to be declining. In the region bycatch and oil pollution at sea are the main risks.

Scientific name

Hydrobates monorhis | (Swinhoe, 1867) (GBIF: Oceanodroma monorhis)

Swinhoe described the species in 1867 as Thalassidroma monorhis; because it was later moved to another genus, the author and year stand in brackets. The genus Hydrobates was introduced in 1822 by Boie. Hydrobates is Greek, from hudro- 'water' and batēs 'walker': 'water walker'. monorhis is Greek, from monos 'single' and rhis 'nose', for the fused nasal tube. The specimen the first description was based on came from near Xiamen, Fujian, China.