OUWENEEL GL (2001) Rapid increase of breeding barnacle Geese Branta leucopsis in the Delta area, SW-Netherlands. LIMOSA 74 (4): 137-146.

Alter the first settlement of 4 breeding pairs in 1988, Barnacle Geese have shown a rapid increase in breeding numbers in the Delta area, SW-Netherlands (Fig. 1) In 2000, more than 520 breeding pairs were recorded, breeding at 8 different sites (Tab 1), About 95% of the population breeds on (artificial) islands and offshore dams built for coastal defence, There is only one larger colony situated in a mainland area (Beeninger Slikken), Based on the estimated age of goslings, it was calculated that first egg-Iaying starts around 10 April, i,e. when still many wintering birds are present in the area. However, timing of breeding varies from year to year, and timing when first small goslings were observed, ranged from 21 May (1998) to 4 June (1996). Moreover, there is much individual variation and new pairs with goslings may turn up in the first hall of July. At one of the main breeding sites , Hellegatsplaten, about 50% of the adults present were successful breeders (data from 2000). Average brood size was 3.18 goslings/pair (Tab. 2). Breeding birds, goslings and non-breeders congregated in large moulting flocks. At Hellegatsplaten two flocks with a total size of 775 individuals were observed on 12 July 2000. In the second hall of July and in August, these birds moved to a nearby grassland area (Korendijksche Slikken). Here, 4000 Barnacle Geese were observed on 10 September 2000, about a month before the first northern breeding birds arrive to winter. Together with one other post-breeding flock, the size of the total population of Barnacle Geese in the Delta area is estimated at 4200 individuals. It is not known whether these birds mix with northern birds in winter.
      The rapid growth of Barnacle Geese in the Delta area and elsewhere in the Netherlands, show that the species is well able to adapt to breeding in temperate zones, as shown before by successful settlements in the Baltic in the 1970s. The origin of the breeding birds in the Netherlands is thought to be a mixture of escaped and wounded birds, which now have founded a virtually wild population. In the Delta area, the population increase was enhanced by the numerous islets and dams for coastal defense, which have been built from 1987 onwards. These provide the birds breeding opportunities without risk of ground predators, a situation which is very similar to the original breeding areas in the Arctic. One single Fox which was able to reach the colony in Markiezaat in 1999, showed how the breeding output can be reduced when predation would occur on a larger scale. In near future, the number of islands and dams will still increase in the area. Hence, the population will probably continue to grow and expand to other sites. However, as shown by some of the larger settlements (e.g. Markiezaat and Beeninger Slikken, Tab. 1), density dependence could stop the ongoing increase at least on a local scale. Unfortunately, there is no information at all about mortality and reproduction in this breeding population, so it is difficult to judge how long and to which level the population will expand.Barnacle Goose Branta leucopsis

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