February 9th, 1999
A number of
predators use the school grounds and although it is
possible to observe some of these, such as kestrels,
during the daytime those that hunt at night-time present
more of a challenge. One of these is the tawny owl.
During the warmer months, individual tawny
owls can be located in the trees at the end of the
cricket field but for much of the year it is more
difficult to find evidence of their presence.
Fortunately, tawny owls regurgitate 'pellets', which
contain the undigested fur and bones of their prey, and these drop to the ground below their
favourite perches. Careful searching will usually uncover
some of these below the trees where the owls are normally
seen.
The bones
illustrated on this page come from several pellets that I
picked up during the past week. Most of the images are
much larger than the original
bones. The largest ones, from the legs, were as much as
twenty five millimetres in length but some of the teeth
were only one or two millimetres long. Despite their
small size, the bones exhibit a number of interesting
features when viewed through a hand lens. For instance,
tiny ball joints can be seen on some of the leg bones and
a variety of types of teeth can be seen. The
lower jaw bones survive the digestive process more
readily than some other bones, such as ribs, which were
almost absent from the pellets examined, and these are
particularly useful when trying to identify the prey
species.
Most of the
pellets that I have found recently seem to be quite old.
It may be that the tawny owls do not always use the
grounds or it may be that the increase in population
during the summer months, when the young will also be present for
some time after fledging, leads to more evidence of the
presence of this species at this time. Although I often
hear little owls in the grounds, I do not hear tawny owls
very often. A concern at the moment is that modern
farming machinery is damaging an old, ivy-covered ash
tree which grows in what used to be a cricket field and
is, I believe, probably a favourite tree for the tawny
owls. Recent ploughing of the field has severed a number
of roots on the tree, one as thick as a person's thigh,
and this must bring closer the day when the tree will
fall down or when the farmer will decide that its poor
condition merits it being chopped down.
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