KLEEFSTRA R (2014) Little Gotland: breeding Barnacle Geese Branta leucopsis in the National Park Oude Venen in 1999-2010. LIMOSA 87 (4): 193-202.

The first breeding pair of Barnacle Goose in National Park Oude Venen, in the Dutch province of Friesland, settled in 1999 (Fig. 3). From 2005 onwards the colony on a small island has been surveyed to monitor the number of breeding pairs and assess breeding success (Tab. 1). In 2009 also 19 nearly fledged young and 14 locally breeding adults were colour-ringed. In 2005 the breeding population on the island had increased to 71 pairs, and with additional pairs in neighbouring swamps the total population in the area numbered 85 pairs. Numbers peaked in 2009 with 92 nests on the island, and an additional 53 elsewhere. In this year, Red Fox Vulpes vulpes and Brown Rat Rattus norvegicus discovered the island and preyed on eggs and geese, leading to a crash to only six pairs on the island in 2010. The high predation pressure leads to displacement of breeding birds to the surroundings, as confirmed by sightings of colour-ringed birds. The total population increased further slightly to 178 pairs in 2010. Sightings abroad showed dispersal to colonies in northern Germany, including adult birds.
During 2005-2010, 382 nests were monitored (Tab. 1). Annual mean clutch size varied from 4.6 to 5.3 eggs. Of all eggs, 46.8% hatched successfully. Intraspecific egg-dumping was recorded in at least 56 nests, inter-specific nest dumping in another 41 nests (Tab. 2). Fledging success was generally low (Fig. 4): less than 10% of all eggs resulted in a fledged gosling. There was evidence for density-dependent gosling mortality, caused by the rather small area of suitable vegetation where goslings were reared. The developments described in this paper mirror at a small scale earlier observations in the newly established breeding colonies on the island of Gotland in the Baltic.

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