Status and population viability of Icelandic Greylag Geese Anser anser in Scotland
During 2003–2007, the Icelandic Greylag Goose Anser anser population increased from c. 73,000 to c. 100,000 individuals (reversing a decline in numbers recorded during the 1990s), the wintering distribution shifted northwards (c. 60% to Orkney) and breeding success (the proportion of adults which successfully raised young) increased. Count, productivity and re-sighting data were analysed to identify any important relationships between the demographic variables (survival and productivity) influencing population trends and intrinsic and extrinsic covariates. In particular, a population model was developed to permit exploration of the effects of recent changes in UK shooting pressure and predict how the population may respond to possible future shooting scenarios. The model suggested that the shooting of Icelandic Greylag Geese in the UK has declined since 1999, to the extent that by 2007 around 8,000 fewer birds were being shot annually there, probably as a consequence of northward shifts in wintering distribution. Model projections based on this reduced shooting level predicted a median population size of c. 220,000 birds after 25 years, with no risk of decline to below 50,000. In contrast, a return of shooting levels in the UK to previous levels (c. 15,000–25,000 birds per annum) gave a predicted fall in the median population size to c. 55,000 geese after 25 years, with 6% of simulated populations falling below 25,000. The model suggested that a reduction in shooting of 2,000 geese annually (considerably fewer than the estimated reduction of 8,000) would permit population growth in ≥ 50% of simulations. In order for > 95% of simulated populations to have positive population growth, a reduction in shooting of 8,500 birds would be required. Loss of breeding habitat as a result of hydro-power developments in Iceland may reduce the overall productivity of the population, although the estimated current extent of habitat loss appears unlikely to have a significant impact on the population. This result is based on limited data however, and further developments may change this situation.
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