Ibis (2007), 149, 553–563 © 2007 The Authors Journal compilation © 2007 British Ornithologists’ Union Blackwell Publishing Ltd A demographic comparison of two Nordic populations of Greylag Geese Anser anser PIERRE A. PISTORIUS, 1 * ARNE FOLLESTAD, 1 LEIF NILSSON 2 & FRANCES E. TAYLOR 1 1 Norwegian Institute for Nature Research, Tungasletta 2, N-7485 Trondheim, Norway 2 Department of Animal Ecology, Ecology Building, SE-223 62 Lund, Sweden Greylag Geese Anser anser have been neck-banded on an annual basis in Scania, southern Sweden since 1984 and in Norway since 1986 as part of a Nordic Greylag project. This has yielded a large database of resightings, which we used here to estimate and compare survival rates between the two populations by means of mark–recapture models. Estimated adult survival was sex-dependent in the Scanian population, probably a result of differential neck band retention rates in this population. Mean juvenile survival was about 12% higher in the Scanian population (0.603 vs. 0.485). Adult survival in the Norwegian population was 0.728 (males 0.733; females 0.725), and in males and females from the Scanian population was 0.711 (0.752 after accounting for higher neck band loss in males) and 0.771, respectively. Over the course of the study, juvenile survival in the Scanian population increased substantially, and adult survival was constant, whereas both these parameters declined in the Norwegian population. This study demonstrates that the two Nordic populations are demographically distinct and gives further support to the notion that they should be treated as separate management units. The decline of 10% in adult survival in the Norwegian population, the cause of which still remains uncertain, is likely to have had a major impact on the growth of this population. In both Norway and Sweden, Greylag Goose Anser anser numbers have increased rapidly since the mid 1970s after previous over-exploitation (Fog et al. 1984, Madsen 1991, Follestad 1994, Kampe-Persson 2002). These growing numbers have had serious management implications in recent years as a result of Greylags contributing to large amounts of agricultural crop damage, in conjunction with them being favoured as a target species by hunters (Follestad 1994). This motivated a study that examined seasonal survival parameters in Norwegian Greylag Geese (Pistorius et al. 2006a). Results indicated a significant recent decline in survival in adults from this population. Several studies on long-lived species such as Greylag Geese have demonstrated the primary role that survival (particularly in adults) rather than fecundity plays in setting the rate of population change (Le- breton & Clobert 1991, Sæther et al. 1996, Rockwell et al. 1997, Schmutz et al. 1997, Menu et al. 2002, Pistorius et al. 2004), and it is consequently expected that these observed changes in Greylag survival would have had a large impact on the population growth rate (Pistorius et al. 2006a). The above results were derived from a long-term mark–recapture programme initiated as part of a Nordic Greylag project (Andersson et al. 2001). Marking and resighting of Greylags from Scania (southern Sweden) and Norway began in 1984 and 1986, respectively. The most recent estimate of the Norwegian population was approximately 10 000 breeding pairs (Follestad 1994), approximately the same as the Scanian population (Nilsson et al. 1999, Andersson et al. 2001). Motivated by the recently reported decline in sur- vival in the Norwegian Greylag population (Pistorius et al. 2006a), we used mark–recapture models to examine the effect of sex and year on juvenile and adult survival of Greylag Geese from Scania over the period 1984–2003. We further estimate annual (rather than seasonal; Pistorius et al. 2006a) adult survival in Norwegian Greylags for the period 1986 – 2001 to compare survival patterns between the two populations. Despite some ecological differences between the two Nordic populations (see Discussion), the fact that Greylags from both populations stage in *Corresponding author. Email: ppistorius@zoology.up.ac.za