The sole representative of its genus, Blue Petrel Halobaena caerulea is a small Procellariiform closely related to prions, genus Pachyptila (Warham 1990, Penhallurick & Wink 2004). It breeds between September and March on the Diego Ramírez Islands, islands around Cape Horn, South Georgia, Gough, the Prince Edward, Marion, Crozet, Macquarie and Kerguelen archipelagos, and perhaps on the Falklands (Watson 1975, Harrison 1983, Woods 2017, Savigny 2021).

Figure 1.

Blue Petrels Halobaena caerulea in Uruguay. A: Barra de Laguna de Rocha, dpto. Rocha, 11 October 2005 (Martin Abreu); B: above, Playa Bella Vista, Maldonado, 21 May 2016, below, La Paloma, dpto. Rocha, 8 July 2018 (Diego Castelli); C: off dpto. Rocha, 22 June 2021 (Joaquín Muñoz); D: off dpto. Rocha, 18 July 2022 (Joaquín Muñoz)

Figure 2.

Plastic items found in the ventricle of a Blue Petrel Halobaena caerulea (MNHN 7080) from La Paloma, dpto. Rocha, 8 July 2018 (Joaquín Muñoz)

The species is mainly distributed in cold waters near the Antarctic Convergence and is quite sedentary, remaining close to the breeding islands throughout the year (Harrison 1983, Howell & Zufelt 2019, Savigny 2021). However, during the non-breeding season it can move north, via the Humboldt Current to 40°S in Chile, and exceptionally to 23°S in the Atlantic Ocean (Teixeira et al. 1984, Onley & Scofield 2007, Howell & Zufelt 2019).

Blue Petrel appears regularly over the southern Argentine shelf (Savigny 2021); however, it is scarce anywhere else in South American waters (Clark 1986, López-Lanús 2020). In Argentina, the northernmost record involved moribund individuals on the coast of southern Buenos Aires province (M. Pretelli;  https://ebird.org/checklist/S47684785). In Brazil just two stranded birds have been recorded: in Rio de Janeiro (Teixeira et al. 1984) and Rio Grande do Sul (Fonseca et al. 2001).

In Uruguay, Blue Petrel is considered occasional (Azpiroz et al. 2012), being recorded for the first time by R. Saccone on 30 July 1973, at the mouth of Arroyo Pando (34°47′S, 55°51′W), dpto. Canelones (Cuello 1975). The specimen is in the Museo Nacional de Historia Natural, Montevideo (MNHN 4153). To date there have been no further published records for the country. Here we provide details of five new records in Uruguayan territory.

On 11 October 2005, MA found a Blue Petrel (Fig. 1A) stranded at Barra de Laguna de Rocha (34°40′S, 54°01′W), dpto. Rocha. On 21 May 2016, A. Pini found a dead male at Playa Bella Vista (34°48′S, 55°21′W), dpto. Maldonado (MNHN 7077, Fig. 1B). Stomach content analysis revealed squid beaks in its ventricle. On 8 July 2018, MA collected a moribund oiled individual at La Paloma (34°39′S, 54°11′W), dpto. Rocha (MNHN 7080, Fig. 1B). The stomach contained squid beaks in its ventricle and several items of plastic were also identified (Fig. 2).

On 22 June 2021 a single Blue Petrel was observed (Fig. 1C) by JM from a ‘freezer’ fishing vessel in Uruguayan waters (34°55′S, 52°09′W). Water depth was 498 m and SST was 15.5°C. Wind direction was east, speed 2.5 knots. It was differentiated from Pachyptila spp. by the presence of a black ‘beret’, a blackish half-collar and broad white terminal tail-band (Howell & Zufelt 2019, Savigny 2021). It stayed with the vessel for 50 minutes, keeping 20 m away, feeding on discards together with Black-browed Albatross Thalassarche melanophris, White-chinned Petrel Procellaria aequinoctialis, Northern Giant Petrel Macronectes halli, Cape Petrel Daption capense and Pachyptila spp. It competed strongly and successfully with Cape Petrels for food, despite its smaller size.

On 18 July 2022, JM observed another Blue Petrel (Fig. 1D) off Uruguay (35°22′S, 52°29′W), 30 m from the same vessel. Water depth was 691 m and SST was 14.7°C. Wind direction was north-west, speed 25 knots. This observation lasted <1 minute and coincided with large numbers of birds feeding on fish discards including Southern / Northern Royal Albatross Diomedea epomophora / D. sanfordi, Black-browed Albatross, White-chinned Petrel, Southern Fulmar Fulmarus glacialoides, Cape Petrel, Wilson's Storm Petrel Oceanites oceanicus and South American Tern Sterna hirundinacea. In Uruguay, this species assemblage is characteristic of predominantly subantarctic waters (Jiménez et al. 2011).

These records update the status of Blue Petrel in Uruguay and include the first observations at sea in the country, over the shelf-break. Given the few records in the northern south-west Atlantic, it is still considered only an occasional species in Uruguay associated with cold waters of the Malvinas Current, which reaches as far north as southern Brazil (Harrison 1983, Howell & Zufelt 2019, Savigny 2021). All the records reported here, except that in October, were during austral winter, like those in southern Brazil and in Buenos Aires province, Argentina (Teixeira et al. 1984, Fonseca et al. 2001, eBird 2022). This species may be under-recorded because it is usually associated with prions of similar size and plumage, meaning that it could be easily overlooked, especially at longer ranges (Warham 1990, Howell & Zufelt 2019, Savigny 2021). Furthermore, Blue Petrel does not usually approach fishing vessels (Onley & Scofield 2007), decreasing the likelihood of it being observed at sea. Further survey effort could shed additional light on the species' presence in the region.