A nationwide survey has been launched to discover what garden berries and fruits birds find most appetising during the autumn and winter. The Birds and Garden Berries Study from the British Trust for Ornithology (BTO) is the first full-scale attempt to investigate the subject. ‘Fruits and berries provide rich pickings for birds in gardens, but we know very little about which ones different birds require and why,’ explains Tim Harrison of the BTO’s garden-ecology team. ‘Is colour important, for instance, or is the timing of the fruiting period more crucial?’

As some farmland bird species continue to struggle, despite a range of agri-environmental schemes being introduced, private gardens are becoming increasingly significant in supporting the avian population-they now represent a larger area than that of the national and RSPB nature reserves combined, a trend that is set to continue as the human population expands. ‘Our year-round Garden Birdwatch Survey shows seasonal differences, with peak use often coinciding with periods of food shortage beyond the garden gate,’ reports Dr Harrison. ‘Gardens appear to provide a lifeline for birds at many different times of the year.’

One advantage is that gardens often contain non-native berry-producing trees and shrubs that may attract some birds because of their nutritional content or timing. Although the study’s main focus is on the use of berries by wintering thrushes (blackbirds, song thrushes, mistle thrushes, fieldfare and red-wing), gardeners and bird-watchers are encouraged to submit records on other species feeding on berries, such as waxwing, blackcap, starlings and woodpigeons.

The survey forms part of the BTO’s broader Winter Thrushes Survey, which looks at the fortunes of thrushes in the countryside. Volunteers are asked to contribute records for a local area or to take on a specially allo-cated survey square. ‘Prolonged freezing weather sees many members of the thrush family, such as redwing, fieldfare and mistle thrush, pour into gardens,’ explains Dr Harrison. ‘However, these birds move around during much of the winter and we need to find out in what numbers and where, and which habitats are most important.’

Poor crops of wild fruit and seed are widely forecast after the wet, cold summer, so the BTO will be looking closely at the impact on wintering thrush numbers. The charity Plantlife reports a good crop of blackberries, which are summer-flowering plants, at its Ranscombe Farm reserve in Kent, but sweet chestnuts are behind and sloes, which come from the spring-flowering hawthorn, are proving hard to find.

To join the BTO’s survey, telephone 01842 750050 or visit www.bto.org

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