de Schneidauer T.R. (1968) La population expérimentale d'Oies Cendrées dans la reserve du Zwin. ARDEA 56 (3-4): 228-247

The author gives details of the population growth of an experimental flock of Grey Lag Geese (Anser anser) during ten years, 1956-1966, in the nature reserve The Zwin, near Knokke, Belgium. The Grey Lag Goose is extinct as a breeding bird in Belgium for about one century. In the Netherlands the last nest of the species found before the incidental creation of new breeding grounds in the IJsselmeer Polders, was in 1909. In 1955 Count Lippens, promoter of the nature reserve The Zwin, succeeded in obtaining 3 pairs of pinioned Grey Lag Geese from Russian origin. These birds therefore were pure or almost pure-bred Anser anser rubrirostris. The birds started to nest in 1956, producing 4 goslings. The number of goslings reared in the subsequent years is given on page 230. By the end of 1966 a population of 300 full-winged Greylags originating from the first 3 pairs had established itself in The Zwin area. This flock was studied by the author for eight years, providing numerous details on breeding and feeding behaviour, biotope requirements, growth, moult, and migration. The annual production of goslings varied considerably. The minimum average production rate seems to be about 25 goslings a year. The birds which move about freely in the immediate surroundings make use of a protected area of about 2,000 acres with a variety of habitats with fresh, brackish and salt water, including rich meadows and salt marshes. The capacity of the area seems to be limited to about 200 resident geese. Any surplus numbers leave the area in winter to join the migratory movements of wild birds of the western continental race anser. As all young birds are ringed (in some years with additional coloured rings) the movements of a large part of the flock can be followed, but unfortunately rings used in the early years were less durable and apparently most of these have been lost through wear. In 1966 at least some 100 of the population of 300 geese had developed migratory habits, subsequently providing recoveries from the Netherlands, France, Denmark, and Sweden. Of 38 adults and 213 goslings ringed in 10 years there are 15 recoveries (12 of which were immature birds), giving a low recovery percentage of about 5%. With only one exception all ringed birds recovered were shot. The influence of weather conditions on the annual production of goslings is discussed. Particularly in dry spring seasons the reproduction success was below the average. For reimplantation attempts in the Netherlands the Zwin Biological Station presented 10 goslings of the 1960 breeding season to the Institute for Applied Biological Research (ITBON), Arnhem, Netherlands. Further cooperation, including the supply in 1967 of a complete family of Greylags to the International Biological Program (IBP) workers at Terschelling is anticipated.