Press release from RSPB Scotland (12 December 2023):
Lambs not a major food source for breeding white-tailed eagles in Scotland
New study finds proportion of nests with evidence of lamb as prey declines over 20-year period
A new study assessing the diet of breeding White-tailed Eagles (Haliaeetus albicilla) – also known as Sea Eagles – in Scotland between 1998 and 2017 has found that marine prey of seabirds and fish is the most important food source for them, whilst the occurrence of lamb in their food has decreased as more pairs have established.
Analysis of food remains shows an incredibly diverse diet during the breeding season; 11,375 different food items were recorded in 293 samples from nest sites in 92 White-tailed Eagle territories across Scotland and 121 species were recorded with 70 species of bird, 17 species of mammals and at least 30 species of fish.
The study, published as a peer reviewed paper “The breeding season diet of White-tailed Eagles in Scotland” in the Scottish Ornithologists’ Club journal Scottish Birds, began in 1998 when there were only 18 pairs of White-tailed Eagles in Scotland, mostly in the Inner Hebrides. By 2017 there were at least 122 pairs across the country, and 58 nests were sampled in that year.
The analysis showed that in that time the proportion of lamb remains in nests have decreased; at the start of the study period between 1998 and 2002, 15 nests were sampled and lambs accounted for more than 30% of items in five of those nests. However, as the White-tailed Eagle population expanded, pairs establishing in new territories tended to feed on fewer lambs, so by the end of the study in 2017 lambs accounted for 30% or more of items at five of 58 nests sampled.
White-tailed Eagles are major scavengers, with inexperienced birds from the first round of releases in the 1970s and 1980s attracted to areas where dead sheep or lambs were readily available. A previous study found that lambs tended to be scavenged when already dead and as carrion. That study also indicated that on occasion live lambs were killed, however that these lambs taken were often smaller than average so more vulnerable to predation.
Despite many hours of field observations in other monitoring of White-tailed Eagles the scale of live lamb predation has proved very hard to quantify. Following the original settlement pattern on the islands of Mull and Skye in particular subsequent generations began breeding in areas where natural live prey was more readily available, with a shift in diet as a result. In its conclusion the paper states that “the previously widespread view that lambs are an important food for White-tailed Eagles has been superseded; the prevailing evidence now is that marine items (seabirds and fishes) are the most important breeding season food in Scotland.”
The most common species found in nests is now Fulmar – 30% of items per nest – with lamb now only accounting for 6% on average. As this study was based on prey remains, fish, young birds and smaller items are likely to be under-represented in it as these remains are more easily digested or decomposed. The result is that this study will have over-estimated the importance of large mammals and birds in the diet.
The study also recorded differences in diet based on the geographical location of the nests, supporting previous studies that show White-tailed Eagles are generalist foragers – taking a wide range of prey types – and able to adapt their diet to what is readily available locally. At coastal territories seabirds and fish made up most of the food remains. At nests in territories further in inland foods such as wetland birds and rabbits dominated. The study authors note that as White-tailed Eagles continue to recolonise historic territories away from the coast species such as Mountain Hare and freshwater fish are likely to become important food sources.
The paper is an important contribution to the growing body of knowledge about the diet of these birds with robust field data and analysis vital in feeding into policy and management, such as the Sea Eagle Management Scheme (SEMS) promoted by NatureScot to support farmers and crofters in areas where White-tailed Eagles are present. The SEMS is due to be reviewed and updated in 2024.
The paper authors highlight that as the study method focused on nests where breeding was successful, future studies using tracking devices on eagles to monitor foraging behaviour and identify feeding perches will be needed to help identify food remains of juvenile or immature birds, and adult birds outside the breeding season.
Robin Reid, one of the paper authors said: “This publication has been made possible through collaboration between many researchers and fieldworkers and with support from several organisations. As a result, the findings are based on large and robust dataset with prey remains collected from the majority of White-tailed Eagle territories occupied in Scotland during the study period. It has been fascinating to see how the diet varies between individual territories and across regions. The wide range of prey items recorded demonstrates that the White-tailed Eagle is an opportunistic and adaptable predator and scavenger, consistent with findings from studies elsewhere across the species range in Europe.”
Eilidh McNab, Development Officer for the Scottish Ornithologists’ Club who published the paper said: “The SOC is delighted to support the publication of important research in Scottish ornithology through our quarterly journal, Scottish Birds. It is fantastic to see the return of such charismatic and iconic species as White-tailed Eagles to Scottish skies, and it is heartening that the population is expanding into areas where they have not been seen in over a century. This paper offers a fascinating insight into the diet of our largest bird of prey, and greatly adds to the knowledge base of their feeding behaviours in Scotland.”
Duncan Orr-Ewing, Head of Species and Land Management at RSPB Scotland and member of the National Sea Eagle Stakeholder Group said; “This study will be invaluable for an evidence-based approach when drawing up the next Sea Eagle Management Scheme and targeting of available resources to geographical areas where support is most needed. We also hope that the results of this study will provide some reassurance to famers and crofters in connection with their concerns about livestock predation and when noting the largely natural diet of most breeding White-tailed Eagles in Scotland.”
ENDS
The paper’s full citation is as follows:
Reid, R., Grant, J.R., Broad, R.A., Carrs, D.N. and Marquiss, M. (2023). The breeding season diet of White-tailed eagles in Scotland. Scottish Birds 43(4): 305-318.
Unfortunately this paper is not ‘open access’ so I’m not allowed to publish it here. If you’d like to read it you’ll either have to become a member of the Scottish Ornithologists’ Club or contact one of the authors directly for a PDF.
Raptor Persecution UK 
A Pdf of the article is also available on Researchgate: https://www.researchgate.net/publication/376191616_The_breeding_season_diet_of_White-tailed_Eagles_in_Scotland
[Ed: But still behind a paywall]
Hi Editor, I just pressed ‘download full text PDF’ and it let me, despite what was said on the page suggesting one had to join first. If that helps. Regards, Niall
Another great piece of research that really should inform any future debates in the various UK parliaments but I can’t help feeling that the farming and other vested landowner interests will continue to dominate, as they have for decades and probably centuries.
Here’s the summary of a 1969 paper following a detailed field study into ‘predation of lambs’ by corvids in Australia by Ian Rowley:
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AN EVALUATION OF PREDATION BY “CROWS” ON YOUNG LAMBS
Ian Rowley – May 26,1969
Summary
In south-east Australia, Corvus coronoides and Corvus mellori are slow to reach sexual maturity and spend their immature period in nomadic flocks. Seasonal fluctuations in the numbers of corvids present in any one district correspond to differences in the availability of food and are due largely to the movements of nomadic flocks. Lambing flocks of sheep provide a local abundance of food, mainly in the form of afterbirths and carrion. Few healthy lambs are killed by corvids but many sick animals are finished off by them, a distinction not appreciated by most farmers. Dystocia, twin births, weakness, and desertion are the main circumstances that predispose lambs to serious attacks. Aviary experiments suggest that on the south-east mainland of Australia C. coronoides and C. tasmanicus are the only species capable of damaging lambs.
A change in sheep management, particularly by providing shelter for lambing flocks, will ensure a greater and more permanent improvement in lambing results than will control of corvids which at best has only a temporary effect.
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Upland farmers make a choice to farm in the way they do. Protecting new born lambs – or not – is a choice and while landscape and economics may inform that choice, it is nonetheless a choice. Shepherd’s huts are not just chi-chi middle class garden adornments, they have a real function in allowing lambing to be supervised and predators to be discouraged. Weak lambs are brought in by the shepherd until they are healthy enough to survive.
If these methods are not desired or even unaffordable then losses to predators are a natural consequence of that choice. In any case, ‘predation’ by mammals and avians is a tiny factor in lamb losses compared to birth defects, hypothermia, abandonment by the ewe etc. We can’t blame nature for cleaning up the mess we leave.
One final point; eagles and other natural predators all evolved in the absence of lambs.
This is a nice read, especially after reading such doom and gloom regarding birds of prey and the shooting industry, this is a positive article.
Although it is sad that a few lambs have been killed, or scavenged, it is good to hear these amazing birds can adapt to the surroundings, and prey availability.
The vast majority of lambs are bred to be slaughtered anyway, and if the eagles are taking the weakest, most vulnerable lambs, it is less feed the farmer has to supply, not really a positive, but a different way of looking at it.
If the seas were not overfished the eagles would have more natural food available, and would not need to find alternative food supplies,but that is another story.
I have not been lucky enough to see one in the wild yet, due to abominable weather when I visited mull, these are a bird on my ‘to see list’, along with hen harrier, and golden Eagle, I have been lucky enough to see osprey here in Norfolk a few years ago, adults and young, fishing from an old quarry turned over to a nature reserve.
I did sea a golden Eagle in Scotland, but it was so far away I didn’t get a good look, and it was only visible for a short time before going behind a mountain.
I hope this report had been seen by the mp on the west Coast of Scotland, the one who was trying to get a kull order on the white tailed eagle, apparently he believes the lambs are more important to Scotland than its native wildlife, the same view and mentality as the gamekeepers who believe game birds are more important than birds of prey, which are also native to our country, unlike game birds.
The human thirst for killing stuff for fun is probably human kinds biggest flaw, along side destruction of natural habitat.
Then we have those who get enjoyment out of using dogs to kill wildlife for fun, or chasing foxes on horseback with a pack of dogs they chase down and rip the animals apart for the enjoyment of the humans on horses, I don’t understand this pastime, and I am glad it has been banned, like all things illegal, it still goes on, but now they call it an accident, or unintentional, however, if they were not charging across the countryside with a pack of dogs it would not happen, and if they bothered to check the surroundings first they would know foxes and badgers live in those areas, who am I kidding, they knew about it anyway, that’s the whole reason for them to be in that spot in the first place, after all its not as entertaining chasing a scent.
Then there are those who think a pole snare, or poisoned bait is a normal activity, and is perfectly legal, or that’s what they would have you believe, but we all know these people do not live under rocks, and are fully aware of the laws regarding killing protected species.
The biggest problem by far is the legal systems inability to offer appropriate sentences, and it’s complete disregard towards wildlife crimes, almost as if they don’t matter, or perhaps because it could impact their shooting club, the vast majority of oiks with guns come from affluent backgrounds, ie, judges, lawyers, mps, etc, the comon theme is wealthy people with no morals, and no idea of the damage being caused , the ripple effect from killing a parent bird of prey which is trying to feed its young, or raise young, without their food supply these young birds will starve, and all because of greed, in the name of sport.
Sport and religion go hand in hand with the world’s biggest problems, most wars are because of religious belief, my god is better than yours, and all that nonsense, sport is all about the individuals involved getting their kicks from my team is better than yours, or my sport and entertainment is more important than nature, and wildlife, I want to kill more birds for the sake of it.
Society has not really moved on from victorian times, when shooting, and hunting was one of just a few hobbies available, nowadays with so much more entertainment available and so many more ways to have fun, we still have the same mentality towards killing stuff for fun.
The only shooting I do is with my camera, I try my best to not disturb the subject, and don’t leave more than a footprint behind.
Let’s hope xxxxx xxxxx xxxxx reads this brilliant report. WTE’s diet is mostly fish. Besides, crofters get perfectky good compo for losses. It would help considerably though, if claims weren’t exaggerated!
Let’s hope they’re not eating the farmed salmon up there in Scotland!
Exaggerated? One South Uist township reckons they are taking calves!
And Kites are still carrying off chihuahuahs and pugs!? If only.