Grazing Ecology of Barnacle Geese (Branta leucopsis) on Islay

A large increase in the number of Barnacle Geese wintering on the Inner Hebridean island of Islay has brought them into conflict with local agriculture. These geese were found to cause major widespread losses in the availability of grass to farm stock in the early spring. On areas which suffered particularly high levels of goose grazing, there were also substantial reductions in silage yield. The geese caused further loss in yield by delaying the spring application of fertilizer. Goose grazing did bring about some improvement in the quality of the sward, through an increase in its protein and a decrease in its fibre content, but this benefit was negligible in comparison to the large quantitative losses. There was no doubt that the geese were having a major impact on the island's agriculture. Several refuge areas have been set up in an attempt to reduce this agricultural impact, where grassland is being managed to support as many geese as possible through the winter. Experiments have shown that reseeding with commercial seed mixes and fertilizer application can both increase the number of geese that a specific area can support substantially. However, the high site-fidelity shown by the geese, both within and between winters, meant that this management was not greatly effective in increasing the numbers of geese using the total area of the refuges. Improvement of grassland attracted local birds, but did not affect the distribution of birds feeding elsewhere on the island. The geese were found to be tolerant of human disturbance, and current levels of scaring were ineffective in bringing about large-scale movements of birds to the refuge areas. Birds were remaining faithful even to the most heavily disturbed area. There was some interchange of birds throughout the winter with the rest of the Greenland Barnacle Goose population, using other sites along the west coast of Scotland and in Ireland. Changes in feeding conditions at these other sites could affect the numbers wintering on Islay, so the Islay birds must be considered as part of the whole population. Breeding success of birds using different parts of the winter range were found to differ significantly. Some evidence was found that suggested that this was due to birds which associated during the winter staying together through other times of year and therefore experiencing similar environmental conditions. More study is required before the factors affecting the numbers of geese coming to Islay are fully understood