The nest of a White-tailed Eagle can be a bulky affair, with those used in successive years taking on huge proportions, as both male and female may add materials to an already impressive structure. Made primarily of sticks and branches, it is not unusual for nests to measure up to 2 metres across and 1 metre deep. A giant nest, which had been built upon over a number of years, was found to be 3.7 m (12 feet) in height.
White-tailed Eagles often have several eyries within their home territory. Being long-lived and faithful to these territories, individual nests may be used for several years, sometimes for decades by successive generations of birds. One nest in Iceland was recorded to have been in use for over 150 years! In parts of the White-tailed Eagle’s range, it has been known for trees to collapse under the enormous weight of such nests.
Site Faithful

White-tailed Eagles on Mull are content to remain faithful to an eyrie’s location as long as it is successful. Should a nest fail, for whatever reason, the adult birds often prove reluctant to employ this location for their next breeding attempt. However, the abandonment of such nests does not necessarily mean the abandonment of a territory. The breeding pair will simply move to another eyrie within the confines of the already existing home range. Often this will be to a location that is in sight of or only a short distance from the previously used nest site.

On the Isle of Mull, as elsewhere in Scotland, the eggs and chicks are supported by a lining of dead purple moor grass or greater wood rush, common plants found throughout the White-tailed Eagle’s foraging range. Nests may be located on cliff ledges or 12 metres (40 ft) or higher in a tree. Both conifers and deciduous trees are used.

During the breeding season, the male will often bring fresh greenery, for example, bracken fronds or bog myrtle sprigs to adorn the lining of the nest. Rather than this being seen as mere decoration, it is thought that this fresh vegetation can assist in helping to sanitise the nest. Many plants on the Isle of Mull possess both antiseptic and antibiotic properties which may help cleanse the nest surroundings of bothersome flies and ticks.

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Cliff or Tree?

Historically, across their former Scottish range, White-tailed Eagles appeared to show a distinct preference for placing their eyries on a cliff face, rather than making a nest in a tree. Nowadays, on the Isle of Mull, thirteen out of sixteen (80%) known eyries are located in trees. Both conifers and deciduous trees are employed, with five nests in recent years being found with the branches of Sitka Spruce Picea sitchensis or Larch Larix decidua, especially on those parts of the island where plantations of these trees predominate.

Lop-sided Inexperience

It is not unusual for precocious pairs of White-tailed Eagles to fail in their initial breeding attempts simply due to their inexperience. This naivety may often show itself in the location that these young birds choose for their early nesting attempts and, indeed, the structure of the nest itself.

A poorly constructed nest may leave eggs, chicks or the entire fabric of the nest at risk during inclement weather and/or unseasonal storms. It is not unheard of for eggs and chicks to fall out of the nest (invariably to their demise) on such occasions, owing to the flimsy and lop-sided nature of the nest becoming saturated prior to collapsing. The photograph (left) was taken earlier in 2013 of a lop-sided nest that was built by a young pair of adult White-tailed Eagles in North Mull.

It came as no surprise that this breeding attempt was one of the few failures to be recorded on the island during 2013. With experience and success the nests of White-tailed Eagles become more rigid and secure pieces of avian architecture capable of withstanding most of what the Isle of Mull’s weather throws at them.