It has been a good year for many trees and shrubs, with an abundance of fruit and berries testament to a perfect season weather-wise. Many of the county’s hedgerows are replete with berries, delivering a blur of ripe red colour as you drive along the lanes. This natural larder, currently well-stocked, will support various thrushes through much of the winter; that is, unless it is hit by a hard and damaging frost.
Many plants produce berries as an incentive to birds which, having ingested the berry and the seeds contained within its pulpy coat, will act as dispersal agents, delivering the seeds ready-wrapped in fertilizer to a new site. Given that plants are not mobile, but rooted to a particular place, this form of seed dispersal enables them to colonize new areas. The relationship between the plants and the birds appears to be a mutualistic one, the plant getting help to disperse its seeds and the bird getting a meal in the form of the pulpy berry that surrounds the tough-coated seeds. However, it is complicated by the fact that some birds eat the pulp but discard the seed instead of ingesting it. Others eat the seed and discard the pulp.
Watch the berries in your garden and you might notice that some seem to disappear just as soon as they ripen, thanks to the efforts of thrushes or Starlings. Other fruits, however, remain throughout the winter and are the last ones to be taken by birds. These differences may be related to the composition of the berries, something which may change as the season progresses. For example, many berries show a decrease in their water content over time, matched by an increase in the quantity of lipids (a group of organic compounds that are made up of oils and fats, and which make up the structural components of living cells) they contain.
You might also notice that differently coloured berries may be taken at different times, with red berries taken before yellow, which in turn may be taken before white-berried forms. Recent research suggests that berry colour may reflect nutritional quality, with berries that are black or ultraviolet-reflecting containing higher levels of certain antioxidants.
While the preferences of birds for particular berries may be more complex than you might have imagined, there are implications if you are thinking about planting some berry-producing shrubs this winter. The key is to provide a number of different shrubs, which offer fruits of different sizes and which ripen at different times, thereby extending the fruiting season throughout as much of the winter as posisble. More advice on what to plant can be found at www.bto.org/gbw/plants.