Jays are magnificently gaudy, garrulous birds (their
Latin name is garrulus glandarius). Mustachioed and
jaunty, they are the spivs of the bird world and
they get a bad press. They are wellknown
egg thieves, and their
predatory tastes extend to
nestlings and chicks.
Together with other
members of the crow
family, such as carrion crows and magpies, they are
classified as vermin and are much persecuted by
game-keepers. But their primary food is the acorn.
The following is based on an article which
originally appeared in “Foret Enterprise”.
During the ice age many tree species and plants,
previously native to Northern Europe, retreated to
Southern Spain, Turkey and Italy. When some 18,000
years ago the ice began to melt, trees and other vegetation
followed the retreating ice northwards to repopulate areas
laid waste by the ice.
The pedunculate oak (the common English oak – quercus
robur) was one of some 30 tree species which reached
Britain before rising sea water, caused by the melting ice,
created the English Channel and prevented further
colonisation. It has been calculated that in order to reach
Britain before it became an island, the oak had to travel
northwards at an average speed of about 500 metres per
annum. But an acorn is heavy and wingless and falls
vertically from its branch. At best, a bounce off a lower
bough might advance its progress by a few metres from
which position it must grow for several years before
producing its own bouncing seed.
There must therefore have been another agent to
accelerate the northward migration. Small mammals such
as mice or squirrels may actually retard regeneration,
while larger mammals such as deer or pigs destroy the
seed in their digestive systems as also do pigeons and
ducks. But jays (and crows) regularly store and collect
acorns.
The jay is a woodland bird and if left alone would have a
population density of one pair per five hectares (approx
12.4 acres). Jays eat only very small numbers of eggs,
fledglings and small rodents. They consume insects all
the year round and caterpillars and seeds in season.
However one seed, the acorn, is eaten all year. Highest
consumption is in the autumn, but jays continue to eat
acorns at other times from their own private stores.
Meticulous research in France has shown that jays prefer
acorns to other seeds, particularly those from pedunculate
oak. Further, they prefer ripe acorns weighing in excess
of 2.5 grams and long acorns are favoured over fat ones.
The jay taps an acorn with its beak and rejects any
containing a weevil or with a damaged shell indicating
fungal infection. It therefore selects ripe, healthy and
long acorns.
The jay carries between four and seven acorns in its
oesophagus plus one in its
beak. In a poor year a bird will
travel up to 10 kilometres to collect
acorns and return to store them in its
own territory. The jay stores the
acorns singly by pressing each into
the ground with its beak, and then
covering it with soil. It buries or plants
acorns only in the transitional areas
between light and shade where there
is little ground cover and where the
soil is soft and moist.
The jay retrieves some 85% of its
stored seeds. If however the stored seed has germinated
by the time it is found, then the jay probes the soil and
eats only the emerging cotyledon. Often this does not
destroy the plant and the acorn will later produce a new
cotyledon with the chance of developing into a tree.
Acorns can be quickly destroyed by predation through
mammals, by drought or by low temperatures. Their
dispersal and storage by jays, protects them from these
dangers and the jay’s choice of storage site ensures that
the seed is placed in a suitable situation for germination.
According to the research, a bird can disperse and store
some 4,500 acorns annually. In areas of controlled natural
regeneration up to 59% of plants can derive from
dispersal by jays and seedlings from acorns buried by
them can be identified by a V mark on the outside. More
oak trees mean more acorns and more birds’ eggs and
more jays and hence more oaks.
In May 1973 I abandoned an old paddock of just over 2
acres and let nature take its course. Today it is a rather
elegant oak wood (see photo). The work was entirely
done by jays.
One good turn deserves another, and so, when I’m out
shooting and a jay flies over, I shoulder my gun and allow
it to pass on its way. A shooting friend, wiser than I, has
suggested a possible compromise for those who worry
about jays’ verminous ways. Shoot them only after the
end of December when their planting program is more or
less complete.
Jeremy Hill
