EBBINGE BS (2004) Unraveling the breeding success of Dark-bellied Brent Geese Branta b. Bernicla. LIMOSA 77 (2): 71-78.

Dark-bellied Brent Geese often nest on small islands in association with Taimyr Gulls Larus heuglini, but can also nest successfully on the mainland tundra within territories of nesting Snowy Owls Nyctea scandiaca, or even more or less scattered without any apparent association with other bird species. Because of year-to-year variations in predator pressure the latter two types of nesting habitat are not available every year. Snowy Owls tend to breed only in lemming peak years (once every three years on the Taimyr peninsula), and the same Snowy Owl territories are not occupied on a regular basis. This means that in order to use these types of nesting opportunities Brent Geese have to adopt a nomadic strategy and have to search for suitable nesting sites immediately after arrival in the breeding area. Year-to-year comparisons of sites where Brent Geese nested within Snowy Owl territories show that Brent Geese did not even attempt to nest in such areas in years when Snowy Owls did not nest there. Within gull colonies, which are predictable from year to year, individual Brent Geese can be very site-faithful, but one would expect a lower rate of return to these gull colonies when more nesting opportunities occur in lemming peak years, when Snowy Owls do nest. Individually marked Brent Geese nesting on islands within Taimyr Gull colonies were studied during two complete lemming cycles from 1990-1995 in the Lidia Bay, Pyasina delta, western Taimyr. Additional information from the wintering grounds allowed us to determine whether individuals were still alive and thus to exclude the possibility of death as a confounding reason not to return. Indeed, more geese returned in the predator peak year 1995 than in the lemming peak year 1994. In the other predator peak year, 1992, Arctic Foxes Alopex lagopus frequently visited the islands by walking across the ice, and the geese abandoned the breeding sites before most rings could be read.
      It is postulated that at the high Brent Goose population levels in the early 1990s, gull colonies were fully saturated as a Brent Goose nesting habitat, and an increased proportion of the population may have had to adopt a nomadic breeding strategy. The recent decrease from 314 000 to 200 000 birds during the last decade is due to a reduction in breeding success, as indicated by the proportion of first-winter birds on the wintering grounds. However, the cause for this reduced breeding success is far from understood. This is reason to resume scientific studies in the Russian high arctic. Black Brant # Brent Goose Branta nigricans # Branta bernicla nigricans

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