Help to find out about birds and berries

It is at this time of the year that I start to see migrant thrushes, newly arrived and busy feeding on the abundance of berries and other fruits that adorn the county’s hedgerows. Berries provide a ready meal for blackbirds, song thrushes and redwings – the latter not arriving in numbers until later into the year – and in return the birds disperse the plant’s seeds into new areas.

Follow the progress of the berries through the winter and you’ll discover that some seem to last longer than others, perhaps because they ripen later or because they are less favoured and are only used when other fruits have been stripped. In some cases, a berry-bearing shrub may be defended by a mistle thrush or fieldfare seeking to secure a food reserve for future use. Whatever the reason, the seasonality of berry availability is likely to be important, influencing where birds feed and when. Taken to an extreme in a species like waxwing, individual birds may range of vast distances to find an area where berries are plentiful.

The interaction between birds and berries is something that has attracted the interest of the BTO, who are running a study this winter to look at how thrushes make use of the berries to be found within our gardens. Some of these garden berries may be native in origin, others introduced and some will be domesticated varieties of wild species. Since berry colour can provide an honest signal to birds of the nutritional value of a particular berry, it is possible that some of the varieties we have selectively bred to produce a particular berry colour (e.g. pink or white) may now be unattractive to the birds. Birds may also preferentially select native fruits over non-native ones, or vice versa – the selection influenced by availability and/or the timing of fruit production.

In order to examine these questions the BTO has asked for our help. By making simple observations of berry availability and of berry use, we can provide the information needed to better understand the relationships that exists between plants and the birds that disperse their seeds. If, for example, non-native plants are favoured over native ones, then this might give them an increased opportunity to become established more widely across the countryside. Could we expect to see Cotoneaster and Pyracantha becoming established in our woodlands and hedgerows? The work should also provide better guidance as to which shrubs to plant for the benefit of our wintering thrushes and other berry-eating birds.

To find out more and to receive a free guide to berries, write to Birds and Garden Berries, BTO, The Nunnery, Thetford, IP24 2PU or email gbw@bto.org.