The
diet of the White-tailed Eagle is extremely catholic and
includes fish, birds, carrion and small mammals. Many birds
exist as scavengers, especially during the Winter months,
feeding on dead deer, sheep and other carrion, as well as
regularly pirating food from otters and other birds, including
other White-tailed Eagles and Buzzards. Studies of food remains
collected from nests, after young have fledged, reveal that over
forty different species of bird, mammal and fish regularly
contribute to the diet of White-tailed Eagles in the breeding
season. Mull's eagles show a preference for Mountain Hares,
Fulmars and strandline birds. For more details of this excellent
RSPB study please
click here.
Photo courtesy of Martin Keivers
Conservative or Lazy?
White-tailed Eagles are nonetheless powerful and effective
hunters. They snatch fish from the surface of both freshwater
and sea lochs on Mull by employing a shallow, feet-first dive.
They have small spikes called spicules on the underside of their
feet which helps prevent slippery prey from escaping. Somewhat
incongruously, White-tailed Eagles have been known to wade in to
shallow water to fish, like a Grey Heron.
The White-tailed Eagle is a
less active hunter than the Golden Eagle and may be seen perched
in a tree or on a rock for hours on end. This has fuelled belief
that it is a lazy predator. The daily food requirement of a
White-tailed Eagle is in the region of 500 – 700g(two large
fish) and equates to about 1/10th of their body weight.
White-tailed Eagles have a longer gut and a more efficient
digestive system than Golden Eagles, which allows them to go for
longer periods without food.
A variety of sea birds and waterfowl are eaten, with Eiders,
Fulmars and Shags being particular favourites. The hunting eagle
will force the swimming birds to repeatedly dive until they are
exhausted, thus making them easier to catch. White-tailed Eagles
on the Isle of Mull have been known to attack and kill
fully-grown birds the size of Greylag Geese (weighing up to 4
kg) and Grey Heron (1.5 - 2 kg).
Intransigence and Belligerence
Photo courtesy of Ian Wilson
The large population of Red Deer on the Isle of Mull usually
provides offal throughout the Winter and, in season,
White-tailed Eagles may take small deer calves, goat kids and
lambs. The latter has been a source of much controversy in areas
of the Scottish Highlands and Islands which support crofting and
farming communities. In places, landowners have shown an
intransigent and, at times, belligerent attitude towards
White-tailed Eagles, owing to the fact that some birds do
predate on lambs. Research, funded by Scottish Natural Heritage,
shows that lambs account for only a small proportion of
an eagle's diet (varying between 4% and 14%) and that
many of these animals are either sickly or dead. It is,
therefore, likely that many White-tailed Eagles are
providing a useful service as scavengers in such
instances.
Kleptoparasitism
Throughout its British
range, the White-tailed Eagle is still often referred to as ‘Sea
Eagle’ and sometimes called ‘Fish Eagle’. The true British ‘Fish
Eagle’ is not even an eagle, but is a name widely given to the
Osprey, which feeds exclusively on fish. All of the White-tailed
Eagle population on the Isle of Mull live close to the sea, on
account of Mull’s island status on the West coast of Scotland.
However, not all White-tailed Eagles breed on the coast, some
preferring to nest inland at freshwater sites, like our famous
pair at Loch Frisa in North Mull.
Throughout their range,
individual White-tailed Eagles are accomplished thieves, robbing
other birds and animals of their prey. The Isle of Mull has an
extremely healthy population of otters, many of whom share their
territories with White-tailed Eagles. Adept at pursuing and
catching fish underwater, otters often bring larger prey items
to the shore to subdue and eat. Ever alert to such
opportunities, White-tailed Eagles can often be encountered
actively harassing these sea mammals, in the hope that the otter
may relinquish its food.
Pellets
White-tailed
Eagles have a swelling in their oesophagus called a crop which
allows them to store excess food without discomfort. The diet of
White-tailed Eagles can be varied and includes fish, birds
(normally ducks and gulls) and mammals, including deer calves
and hares. The indigestible parts of their meals (bones,
feathers, fur and hair) is formed into a pellet in the muscular
part of the bird's stomach called the gizzard and regurgitated
through it's mouth.
White-tailed Eagle pellets may be cast anywhere that the bird
may be resting or roosting, near the nest or in the vicinity of
a favourite place that an individual bird may use to eat the
prey it has caught. The pellets of a White-tailed Eagle can be
large (4 - 5") and predominantly consist of feathers and fur.
Eagles, unlike owls, do not swallow their prey whole. Instead,
they use their beaks to tear at the flesh of their prey, which
means that very few bones will ever be swallowed. Consequently,
no bones should appear in their pellets. By comparison, the
pelleted remains of an owl’s meal will reveal a high proportion
of vole, mice and bird skeletons.
Owl pellet, showing jawbone of
small mammal prey item.
White-tailed Eagle pellet,
showing indigestible feathers and hair. This pellet measures
approx. 4 inches in length.
