Breakfast, Lunch and Dinner

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. White-tailed Eagles on the Isle of Mull appear to show a preference for Mountain Hares, Fulmars and strandline birds. For more details of this excellent RSPB study please click here.

Photo courtesy of Andrew Marshall www.gowildlandscapesphoto.com

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 even been known to wade into 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. They also have a large, flexible pouch (crop), as an extension to their oesophagus, which allows them to store food for later consumption. This may be a useful adaptation when particularly inclement weather on the Isle of Mull precludes hunting.

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. Non-diving waterfowl, like Mallard and Wigeon, are easier targets for a White-tailed Eagle to snatch off the surface of the water than species that habitually dive. In extremis, 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

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.
Photo courtesy of Ian Wilson
Research, funded by Scottish Natural Heritage, shows that lambs (usually) account for only a small proportion of the majority of eagle’s diets (varying between 4% and 14%) and that many of these animals are either sickly or dead. The authors have seen local White-tailed Eagles carrying or eating lamb on the Isle of Mull, but have never seen an eagle actually kill any of these animals. It has been argued that many White-tailed Eagles are providing a useful service as scavengers in such instances.
Do They? Or Don’t They?

On the Isle of Mull, the loss of lambs attributable to White-tailed Eagles can vary from year to year and be dependent on individual pairs, weather during the lambing season and the availability of other prey items, such as rabbits. As a landowner or sheep farmer whose land is presided over by a pair of territorial White-tailed Eagles, it can also be argued that there is a big difference between an eagle that has a taste for lamb and one that hasn’t!

The conflict between sheep farmer and White-tailed Eagles is one destined to promote a dichotomy of opinion for some time to come as plans to re-introduce White-tailed Eagles in other parts of mainland Great Britain gather momentum.

Often overlooked is the number of lambs (dead or otherwise) that are taken by Golden Eagles. There are twice as many Golden Eagles on the Isle of Mull than White-tailed Eagles and the diet of the former, smaller raptor is more specialised. In times of lower populations of Mountain Hare and rabbits during the breeding season, it may be more likely for Golden Eagles to turn their attention to local lambing parks than White-tailed Eagles. Whatever the problem and/or the solution, one thing is without question: the re-introduction of the White-tailed Eagle has provided landowners, hill farmers and those with a grudge with a fresh and very large target to aim at. On the Isle of Mull, we are extremely fortunate that those against the return of these magnificent birds appear few and far between.

Kleptoparasitism

Throughout its British range, the White-tailed Eagle is often still 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.

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 semi-aquatic mammals, in the hope that the otter may relinquish its catch. The authors have witnessed such kleptoparasitic behaviour on several occasions on the Isle of Mull, but have yet to see an otter give up its catch to an eagle, although it, undoubtedly, does happen. To observe a White-tailed Eagle and Otter interact in such a manner on the Isle of Mull would qualify as a once-in-a-lifetime’s experience and something that would live forever in the memory of even the most ardent wildlife watcher!
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 its 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 very large (up to 5 inches) and consist predominantly 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, bones should rarely 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.