Annual and large-scale variation in breeding output of Greylag geese Anser anser in Iceland

Capsule Large-scale variation in breeding output of Greylag geese Anser anser is negligible across Iceland but detectable variation is likely related to spring temperature.

Aims To identify large-scale spatial and annual variation in breeding parameters to support sustainable utilization and conservation of Greylag geese that are a quarry species in Iceland and the UK.

Methods In 2012 and 2013, a total of 360 Greylag nests were visited across Iceland and timing of breeding, egg sizes and clutch sizes were measured. In addition, 888 Greylag families were surveyed in the same period to estimate large-scale variation in brood sizes.

Results Timing of nest initiation varied significantly between parts of the country and nesting started on average on 30 April in West and South Iceland, but considerably later in cooler parts of Iceland, North Iceland (10 May) and East Iceland (20 May). In 2012, clutch sizes were similar between areas but in 2013, East Iceland had a smaller mean clutch size than South and West Iceland. Overall, mean clutch sizes ranged from four to six eggs. Mean brood size varied from three to five goslings per pair between regions, where East Iceland was found to have the smallest brood size on average while West and North Iceland had the largest brood sizes. Brood size was the most variable parameter between years.

Conclusion Regional variation in timing of nest initiation and clutch size across Iceland suggests that variation in these parameters is related to ambient temperatures and this is supported by comparison of data from Iceland and other countries. The South and West parts of Iceland are the warmest and this study suggests that conditions for early breeding may be most favourable there. A more long-term study of the links between demography and environmental parameters is needed for sustainable management of the Greylag population.