STATE OF POPULATIONS AND BREEDING BIOLOGY OF THE HORNED PUFFIN (FRATERCULA CORNICULATA ALCIDAE, CHARADRIIFORMES) IN THE NORTHERN PART OF THE SEA OF OKHOTSK

The breeding biology of the Horned Puffin, Fratercula corniculata, was studied in 1989–2019 on Talan Island, Tauiskaya Bay, Sea of Okhotsk. Even though the estimates of the population size of the Horned Puffin made in the early 1990s and 2007–2008 (90–100 and 75–112 thousand individuals, respectively) failed to reveal its dynamics due to different study methods applied, data on the nesting density in these periods indicated its increase by more than 30%. In subsequent years, higher bird densities were recorded on the surface of model screes. Taking into account these data, the maximum numbers of horned puffins on the island could reach 166 thousand individuals. Depending on ice cover conditions, the dates of the onset of egg laying varied between June 6 in 1990 and June 17–18 in 1987, 1999 and 2001, the average long-term date being June 11. Chicks in different years started hatching between July 17 to 29, the average long-term being July 22. The weight of hatchlings varied from 35 to 53 g (mean 47.2). The average weight of monthly chicks in 1999–2006 ranged from 145 to 329 g, in some individuals from 80 to 410 g. The average age of the young birds captured on the ground was 44.7 days. The first individuals were recorded in different years at the end of August (August 27–30) and at the beginning of September (September 2). According to indirect estimates, fledglings left nest burrows between September 10 and 20, to end in late September to early October. The average weight of fledglings heading to the sea in 1987, 1988, 1989 and 1991 was 349, 338, 347 and 318 g, respectively. The wing length varied from 153 to 156 mm. The reproductive success of horned puffins varied from 10.3 to 90.5% (on average 56.4%), the hatching success from 19.8 to 95.2% (on average 75.5%), the fledging success from 26.7 to 100% (on average 74.6%). In the long-term aspect, the breeding success was most often quite high, with the exception of 2001, 2009–2012 and 2014–2015, when this indicator was lower than the long-term average. Among terrestrial mammals, red foxes cause the main threat to adult horned puffins living on the island, as well as to their clutches and chicks descending to the sea, but foxes fail not render a significant impact on the state of the horned puffin population. Due to their small numbers, these predators control only a certain parts of the island, while horned puffins are dispersed almost throughout its territory, where in most cases they are safe from fox predation. Voles act as utilizers of already abandoned eggs. Slaty-backed gulls and ravens do not attack adult horned puffins, but willingly eat adult birds found dead, as well as dead or still alive chicks during their descent to the sea. Adult birds are also taken, albeit rarely, by Steller’s sea eagles.