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.