Systematic studies of the ornithofauna of the Argentine Islands archipelago by Ukrainian polar explorers began in the second half of the 90s. At the beginning of the XXI-st century, the southernmost breeding site of the Snowy Sheathbill (Chionis alba), Petermann Island, was discovered by Ukrainian ornithologists; later, nesting within the Argentine Islands archipelago was recorded. Breeding and behavioural peculiarities of the Snowy Sheathbill were studied during the XX-th (April 2015 - March 2016) and the XXIII-rd (April 2018 – March 2019) Ukrainian Antarctic expeditions, in accordance with the objectives of the State Target Scientific and Technical Research Program of Ukraine in Antarctica for 2010-2020. The distribution, abundance and detection of the Snowy Sheathbill nesting sites were investigated according to generally accepted methods, by means of surveys on permanent routes, and also by the method of point counting at Cape Marina Point on Galindez Island. During the reporting period, more than 400 hours were spent on conducting morning surveys and recording. The Snowy Sheathbill nests were examined on Galindez and Petermann Islands, the sites of probable breeding were investigated on Uruguay Island and Cape Tuxen (Antarctic Peninsula). In the spring of 2015, at Cape Marina Point on Galindez Island, breeding of one pair of the Snowy Sheathbill was recorded, and in the spring of 2018 – breeding of two pairs. In the spring of 2018, clutches on Galindez Island were registered: in the first clutch - three eggs, in the other – four ones. The average egg weight was 41.0 ± 0.8 (standard deviation – 1.9 g). Under favourable nesting conditions, the hatching of the first chicks is possible in late December. The average weight of newly hatched chicks was 33.3 ± 3.6 g. From January 19 to February 28, 2018, three chicks were weighed: the average increase in the weight of the first chick was 17.9 ± 1.3 g (standard deviation 7.6 g); the increase in the weight of the second one was 17.4 ± 1.3 g (standard deviation 7.7 g); the average increase in the weight of the third chick was smaller than in previous ones and amounted to 13.8 ± 1.5 g. The days without increase in weight were recorded: for the first chick such days were on February 19, 25, 28, for the second one only two days – on February 24 and 28; for the third chick - five days (on February 4, 13, 15, 27, 28). On the 41st day, the weight of the first chick was 680 g, the second one weighed 670 g, and the weight of the third chick was about 480 g. on the 40th day.
Behaviour and breeding peculiarities of the Snowy Sheathbill (Chionis alba Gmelin, 1789) in the water area of the Argentine Islands archipelago and adjacent territories (Graham Land, Antarctic Peninsula)