‘Til Death They Do Part

Photo courtesy of Andrew Marshall

The breeding cycle of the White-tailed Eagle on Mull commences in late Winter, when courtship display and prospective nest site selection may take place. White-tailed Eagles form life-long monogamous partnerships once they become sexually mature. This usually happens when birds are around five years of age, although some individuals may be precocious and attempt to breed at an earlier age. Two pairs of young adults that attempted to breed on the Isle of Mull in 2011 failed due to their inexperience. White-tailed Eagles are remarkably faithful to their partners and to their chosen nest location. Normally, individuals will only form a fresh pair bond should an existing partner die.

Mull’s Veteran Eagles

White-tailed Eagles are long-lived, with the previous oldest recorded bird reaching the age of 32 years. The original pair of birds that settled to breed on the Isle of Mull in the early 1980’s have surpassed this longevity record and are among the oldest White-tailed Eagles anywhere in the world. These remarkable birds have chosen well in life and have reaped the benefit of deciding to settle on the Isle of Mull all these years ago.

Although this elderly pair of White-tailed Eagles failed to breed successfully at their Lochdon nest site in 2012, they are both still to be seen hunting and roosting in the area. Who knows what 2013 may hold for these ‘old timers’? (The 2013 season proved lucky for the island’s elderly eagles, as not only did they attempt to breed, they successfully raised yet another chick. Once again, we take our hats off to the island’s veteran White-tailed Eagles!)

It is inevitable that one or other (or both) of these eagles will perish in the not-too-distant-future. This, indeed, will be a very sad occasion for the island’s Eagle Watch community and will represent something of a watershed in the history of the re-introduction of the White-tailed Eagle to Scotland. On a positive note, however, it would then enable another pair of younger birds an opportunity to establish themselves in what has become a prime location for this species on the island.

Noisy Neighbours

In contrast to Golden Eagles, White-tailed Eagles can be very vocal, especially during courtship and at the onset of the breeding season. This frequent loud calling often takes place in the vicinity of the eyrie and consists of a series of barks or yelping cries that increase in tempo and pitch. Should the adults become alarmed, a loud and far-carrying ‘klee-klee-klee(-klee)’ is uttered, often dramatically piercing the tranquillity of the Isle of Mull countryside in early Spring.
Sky Dancing Pacifists

At the dawn of every New Year, the Isle of Mull’s White-tailed Eagle population readies itself for the onset of yet another breeding season. Although monogamous, individual eagles will be keen to reaffirm their pair bonds with their existing partners and to show fidelity with their chosen breeding territory. This they do in a series of circling and soaring flights, often high above the nest location.

White-tailed Eagles have a characteristic aerial courtship display, which culminates in the pair locking talons in mid-air and whirling earthwards at great speed in a series of spectacular cartwheels. This death-defying stunt may come to an end only a few feet above the ground or water before the birds soar upwards again and can be a thrilling, once-in-a-lifetime experience for many birdwatchers. Displays of this nature most often involve young or recently established pairs, as courtship appears to take on less significance as individual birds get older and pair bonds grow stronger.

Talon-grappling is not confined to courtship display, however, and may be used, by territorial birds, as a way of discouraging intruders. Despite their fierce look and awesome power, White-tailed Eagles often have a pacifistic approach to confrontation, only engaging in physical combat with other birds as a last resort.

Immature White-tailed Eagles often keep the company of similar-aged birds as they roam the wider Isle of Mull countryside in their formative years. By travelling and roosting together these young birds get to know the whereabouts of the best feeding areas on the island. In doing so, these young eagles begin to bond with each other and their playful talon-grappling may be seen throughout the year on the island.

Photo courtesy of Andrew Marshall

Biting Off More Than He Can Chew

Although usually monogamous and faithful to their mates throughout their lives together, sometimes odd circumstances are thrown up which threaten the stability of the Isle of Mull’s White-tailed Eagle population.

During the past five years (2009 – 2013), no fewer than 66 young White-tailed Eagles have fledged from nests on the Isle of Mull. Not all of these immature birds will have survived, but the majority of them probably have. Not all of them will have stayed on the island, choosing to wander throughout Scotland (and beyond) during this time. However, many of them may, indeed, have remained on the island and the oldest of these birds will now be of suitable breeding age. The population of White-tailed Eagles that reside on the Isle of Mull is both dynamic and fluid.

Problems can arise when any sub-adult White-tailed Eagle arrives in an existing territory. Normally, their presence would not be tolerated by one or other of the resident eagles. However, if these disputes take place at the start of the breeding season, this can be enough to cause the failure of that season’s nesting attempt.

Some males, however, seem to enjoy the excitement of ‘extra marital affairs’ and have been known to team up with more than one female at the onset of a breeding season. When this does happen, both females will lay eggs which the male will attempt to help incubate at both nests. This may seem like a recipe for disaster, yet it is not unknown for one of these clutches to hatch and young to be successfully fledged from such an arrangement!