RSPB British Birds of Prey

By Marianne Taylor

This book is a celebration of British raptors (including owls), with 200 stunning colour photographs.

An authoritative text examines the biology and ecology of each species, following their fortunes as British breeding birds from historical times to the present day.

This book serves as a showcase of these fabulous birds and highlights the diverse work of the RSPB in ensuring their survival.

• Language: English
• Publisher: Bloomsbury Publishing
• Release date: Apr 7, 2016
• ISBN: 9781472932259

Marianne Taylor

Marianne Taylor is a writer and editor, with a lifelong interest in science and nature. After seven years working for book and magazine publishers, she took the leap into the freelance world, and has since written ten books on wildlife, science and general natural history. She is also an illustrator and keen photographer, and when not at her desk or out with her camera she enjoys running, practicing aikido, and helping out at the local cat rescue center.

Book preview

Golden Eagle

Aquila chrysaetos

Some birds really do live up to their hype, and the Golden Eagle is emphatically one of them. Though many a claimed Golden Eagle turns out to be a Common Buzzard, when you finally raise your binoculars just as the real deal appears over a distant mountain ridge, you’ll know straight away that you are in the presence of greatness. It is the living embodiment of wildness and remote, forbidding, ruggedly beautiful landscapes. Yet power, beauty, popularity and an attachment to the most human-free wildernesses is not enough to protect the Golden Eagle from those few people who would rather see it dead than traversing the Highland skies.

The Golden Eagle: a magnificent bird of dramatic landscapes.

INTRODUCTION

This is the second largest of Britain’s birds of prey – most White-tailed Eagles are a little larger than most Goldens. For such a large bird, it is beautifully proportioned in flight, with long, broad wings bulging smoothly along the trailing edge of the secondaries, a fairly long tail and a well-projecting head and neck completing its balanced silhouette. Juveniles in their first year are more striking than adults – very dark brown with a broad white flash along the underside of the wings, formed by white bases to the flight feathers, and with a white tail tipped with a wide blackish band. The back of the head and neck have the characteristic golden flush, which is carried through to the paler full adult plumage. Adults lack white in the wings and tails, but have pale fringes to the wing coverts which give them a frosted appearance – the flight feathers and long tail feathers have fine dark barring. Over the seven years it takes to reach full adult plumage, the birds pass through various intermediate plumage stages.

If you see a Golden Eagle at rest, you’ll notice the fairly long, strongly hooked bill with long yellow gape line, rather dark eyes (lightening to amber with age), the feathered lower legs (tarsi) and the long feathers around the upper part of the legs, like a pair of loose, feather trousers. Golden Eagles will spend long spells just sitting, perhaps digesting their last meal or waiting for better weather, and at rest they can look shabby and almost formless – loose-feathered lumps hulking in the branches of a tree, on a crag or in a patch of heather. Getting airborne can be a struggle but once aloft the eagle uses air currents to gain height with little effort, and flying birds are usually seen soaring high on widely spread wings.

Those bright yellowish neck feathers give the bird its name.

TOURISTS’ EAGLES?

Visitors to the Scottish Highlands will often claim to have seen one or multiple ‘eagles’, but many of the sightings would prove, if investigated, to involve Common Buzzards rather than Golden Eagles. The confusion happens so often that many Highlanders nickname the buzzard ‘tourist’s eagle’. Although the buzzard is a lot smaller than the eagle, it is still a large and unmistakably raptorial bird and it is much commoner.

So how can you be sure you’re looking at a Golden Eagle? Size is the first consideration, with the largest buzzard only two thirds the size of the smallest eagle, but when you’re watching a lone bird high in the sky it can be very difficult to assess size. Shape is a much better indicator, and the eagle’s longer-winged and more gracefully proportioned outline may well immediately draw your attention as something different from the wide and round-winged, short-tailed and almost neckless Common Buzzard shape. If you see a Golden Eagle at rest rather than in flight, its bulky shape, big bill and talons and long feathery trousers should help you distinguish it from the more compact and less fearsomely armed buzzard. In short, you might confuse a buzzard for an eagle, but once you see a Golden Eagle, it’s unmistakable.

CONSERVATION IN THE BRITISH ISLES

This is truly a bird of the northern uplands, and its ties to that habitat have always limited its British range. However, during the 17th century it bred as far south as Derbyshire and until the end of the 18th century it still bred in North Wales and in parts of England. In Ireland it just hung on until the early 20th century. Since then, it has been a bird of the Scottish Highlands, with only a handful ever breeding anywhere else in Britain. In Ireland, a reintroduction project began in 2001 and has yielded promising results, but elsewhere the bird’s range and population remains well short of its potential.

The prominent white patches in the wings and tail base identify this bird as a juvenile.

As a very large and fairly visible predator of the uplands, the Golden Eagle was always going to fall foul of grouse-managing gamekeepers in the bad old days of uncompromising predator control. Its presence on grouse moors was not tolerated, and it also raised suspicions among sheep farmers as birds were sometimes seen feeding on dead lambs. In most cases this would have involved lambs that died of other causes and were then scavenged, but there is little doubt that they could take living lambs once in a while. Grouse moors and sheepwalk were both 19th century inventions which spelled big trouble for the Golden Eagle, though it continued to do rather better in forests managed for deer shooting, where it was tolerated. Nevertheless, persecution did eradicate Golden Eagles from England, Wales and Ireland. Its rarity inevitably increased its value to collectors of birds’ eggs and stuffed skins, further pressuring the shrinking population. There was also a small risk posed by unscrupulous falconers or suppliers of birds for falconry, who may have taken nestlings to be trained as working birds.

Two world wars gave the eagles some breathing space as gamekeepers joined other British men to fight overseas. There were changes to the law in the 1950s and 1960s due to the use of organochlorine pesticides such as DDT and dieldrin. These accumulated in the food chain, resulting in eggshell thinning and breakage, and thus increased levels of nest failure, in many birds of prey including Golden Eagles, for which the use of dieldrin in sheep dip was a particular problem. Following bans on the use of these substances in the 1960s, breeding success increased and the first full national survey of Golden Eagles in 1981 found around 420 pairs breeding in Scotland.

Carrion is an important food source, especially for young birds in winter.

Research has helped to show farmers that the impact of Golden Eagles on lambs is inconsequential, resulting in an encouraging change of attitude. Overall, the Golden Eagle is today far more treasured than it is reviled, but illegal persecution is still the species’ biggest problem. Indeed, a Scottish Natural Heritage (SNH) report, published in 2008, concluded that illegal poisoning remains the single biggest factor limiting population recovery.

As Golden Eagles mature, their plumage becomes paler overall, but they lose the white wing patches and tail base seen in juvenile plumage.

Another problem that the Golden Eagle faces is habitat loss and alterations. Upland moors would make unpromising farmland, but one commercial use for the land is forestry. Planting the land with conifers removes both habitat and prey, as deer and sheep are fenced out of the plantations to protect the young trees. Young plantations do offer some hunting and nesting potential, but as the plantation grows it becomes almost lifeless as wildlife habitat. Attitudes towards forestry are changing somewhat now, though, and new plantations are more likely to contain a mix of tree species which harbour a more interesting range of wildlife and more hunting potential for eagles.

Some key Golden Eagle breeding sites have been threatened by proposals to build wind farms. The turbine blades are well known to pose a significant risk to large birds. In October 2009, the RSPB successfully campaigned against plans to build a 14-turbine wind farm near Inverary in Argyll and Bute, on the grounds that it could threaten the area’s Golden Eagles.

Accidental disturbance from walkers and other outdoor enthusiasts may have a minor negative impact on the species too. A study in Norway found a correlation between eagle nest desertion and the timing of the Easter holidays, with more nests abandoned in years with early Easters. This is probably due to higher numbers of skiers around eagle-nesting areas close to the egg-laying time – nest desertion is less likely to occur once eggs have been laid and incubation is under way.

One positive recent development for Golden Eagles is the advent of tracking technology that enables researchers to gain more insights than ever before into the way these birds move around their land through the course of the year. Understanding where, when and how far eagles travel will help landowners plan more comprehensive conservation measures.

THE GROUSE SOLUTION?

Golden Eagles hunt over moorland, and they will certainly prey on Red Grouse – the most coveted of Britain’s gamebirds. Although the majority of gamekeepers abide by the law and leave raptors alone, there are still one or two incidents of Golden Eagle poisoning each year and most of them have occurred in areas managed for grouse shooting. More probably go unreported.

However, grouse-moor managers may be harming their own interests by illegally killing Golden Eagles on their land. While these top predators do take some grouse, their presence also keeps down numbers of other intermediate predators, which do more harm than the eagles by taking primarily chicks rather than adults. A secondary benefit for the moor managers is that Golden Eagles control hare numbers – hares carry the disease ‘louping ill’ which can devastate grouse stocks.

ALMA’S STORY

Alma was the first Golden Eagle to be fitted with a satellite transmitter by Roy Dennis of the Highland Foundation for Wildlife. She was a well-grown chick about a month away from fledging when the tag was fitted in early July 2007, and by August she was seen flying in the vicinity of the nest. The tag, running from a solar-powered battery, was destined to be without power from time to time in the far from sunny environs of the Cairngorms. However, over the next two years a wealth of data was received and published online, showing the young eagle’s explorations of the Cairngorms area and beyond, including a trip all the way to Loch Maree in Wester Ross. Her first breeding season was awaited with great excitement, but she never made it to breeding age – she died almost exactly two years after her tag was fitted.

When the tag showed no movement for several consecutive days, the worst was feared. Her body was found on a grouse-shooting estate in Angus, and it was found she had died from consuming illegal pesticides. A police investigation is still ongoing. Such a dramatic, saddening and shocking conclusion to this bird’s life, which had been followed online by so many, represented a real collision between new ideas and old ways – between pioneering scientists finding more and more ways to study the behaviour of the Golden Eagle in the wild and a few stuck-in-the-past landowners determined that even this most magnificent predator must not be allowed any opportunity to exist alongside the prey they want to keep for themselves.

DISTRIBUTION, POPULATION AND HABITAT

The one long-standing pair of Golden Eagles in the UK outside Scotland in recent years was the famous Haweswater birds which arrived in 1969. Though different individual birds may have been involved, one pair nested or attempted to nest at this stunning Lakeland area up until 2004, when the female of the pair at the time disappeared. From 2005 onwards, the lone male has doggedly remained on territory but has yet to attract a new mate despite enthusiastic aerial displays each spring. Visitors to RSPB Haweswater can witness this spectacle from a viewpoint equipped with telescopes. The male is still relatively young, in eagle terms, so may just attract a young wandering Scottish or Irish female, though his chances aren’t great.

The Golden Eagle’s long legs are feathered almost to the toes, helping to conserve heat.

In Scotland, the species’ distribution shows a north-westerly bias, in accordance with the more remote and mountainous landscape found there compared to the lower-lying and more populated east coast. Many of the larger west-coast islands also hold good numbers, as does the Cairngorms area, and there are a few in the Galloway hills. A pair nested in the Borders until the female was killed (illegal poisoning, once again) in 2007.

Many newspapers and websites published photographs of the body of the poisoned Borders female, which were shocking enough to leave a lasting impression on those who saw them. The impact came not just from the distressing spectacle of the dead bird, but from the sheer size of her body and the spread of her wings, too big for a man to hold fully outstretched. The name ‘Golden Eagle’ is recognisable to all, but these images were a forceful reminder of just what a magnificent species it is, and the story provoked widespread public outrage. In fact, the public response to the case was so great that it led to a full review of what needs to be done to properly tackle wildlife crime in Scotland. Although persecution remains a major problem, this widespread condemnation, which included many voices from within the shooting community, will hopefully lead to those few responsible being further marginalised and eventually to persecution being consigned to the history books, where it belongs.

The UK’s population of Golden Eagles has remained fairly stable at around 440 pairs since 1983. This overall picture, however, masks some fairly dramatic local falls and rises. Numbers on the Western Isles, for example, seem to be on the up while numbers on the eastern edge of the core range have fallen, mainly due to illegal poisoning. The 2008 SNH report found that the most serious problems were in the central and eastern Highlands, on land managed for driven grouse shooting, where less than half of all known territories are currently occupied. The report concluded that many eagle populations in this area were probably not viable in the long run. This concentration of persecution is probably preventing the Golden Eagle returning to former haunts in northern England and possibly Wales.

Golden Eagles have a large world range, extending right across Europe, Asia and North America. While it is very much a bird of the mountains, it is not so much a bird of the north and breeds in upland areas into North Africa, as well as the Himalayas. No other true eagle is more widespread, although its need for large territories and its fairly strict habitat requirements mean it is thinly distributed over much of its range. Estimating world population is difficult but it probably exceeds 120,000 birds and may reach 250,000 – note, though, that up to 30 per cent of those may be non-breeding birds. Europe holds about 8,000 pairs; Spain and Norway are the most important Golden Eagle countries with 1,200 and 1,000 pairs respectively.

In the Republic of Ireland, a reintroduction project is under way as the bird is unlikely to recolonise under its own steam (though a single pair did nest in Northern Ireland from 1953 to 1960). The project began in 2001, and to date several dozen young birds have been liberated in County Donegal. All the youngsters were removed for hand-rearing from Scottish nests that held two small chicks – this temporary harvest should have no lasting impact on the Scottish population as often only one chick out of the two will survive in a two-chick nest (see ‘Sibling rivalry’ for more on this). Breeding first occurred in 2007, and several pairs are now holding territories. Hopes are high for the success of this project, but the worryingly widespread use of poisoned baits in Ireland remains a major concern, and several young eagles have been lost already as a result of this.

STUDYING THE DIETS OF BIRDS OF PREY

Thankfully, researchers don’t have to cut the bird of prey open to look at the contents of its digestive tract, nor must they maintain a 24-hour vigil to record everything it catches. Analysing the diet of birds of prey is much easier than it is for many other animal groups because these predators cough up pellets of indigestible bits and pieces after every meal. By painstakingly analysing these pellets, it’s possible to build up an accurate and detailed picture of what the bird has been eating and in what proportions. Birds of prey also helpfully tend to produce pellets in the same location time after time, making them easy to obtain once the preferred spot or spots have been found.

Raptors eat their prey bite by bite, and bones tend to be either broken up or left uneaten. The most identifiable bits likely to be recovered from their pellets tend to be feathers or hair – bone fragments are more difficult to assign to a species. Owls, which swallow their prey whole, produce pellets containing many intact and identifiable bones.

Techniques more normally associated with crime-scene investigators can be used to tell if an eagle seen feeding on a lamb had actually killed it or not. When a body, be it human or lamb, is still alive, with blood circulating normally, a puncture wound from something like an eagle’s talon will cause lots of bleeding and hence bruising in the body. If, however, the eagle begins feeding after its prey has died, the blood will have stopped circulating, so there will be much less bruising. This has been used very successfully to show farmers that Golden Eagles were only scavenging on lambs that had already died, rather than actively hunting them.

DIET AND HUNTING

The Golden Eagle is a bird of phenomenal power and fearless willingness to take on all kinds of prey. Trained birds have even historically been used to tackle wolves, and it is hard to imagine a more formidable adversary. Yet this great hunter is also agile enough to swipe small songbirds in flight.

Golden Eagles spend much of their time perched – digesting their last meal or scanning for the next one.

In its mountainous Highland habitat, live prey comprises mostly medium-sized birds and mammals of species that also frequent this habitat – Mountain Hares, Ptarmigans, Red Grouse and wading birds such as Curlews. It also takes Fox cubs, Rabbits, voles, mustelids (mammals of the weasel family), small deer fawns and a wide range of bird species which may be as large as geese or as small as pipits. The population breeding on the Swedish island of Gotland are specialist Hedgehog-hunters, owing to a shortage of other suitable prey there, elsewhere they also take the occasional reptile and amphibian (more often in warmer parts of their range). In some areas they are reported to break tortoise shells by dropping the unfortunate reptiles from great heights onto rocks below. They may even eat insects from time to time.

Besides live prey, carrion is an important constituent of the diet, and the Golden Eagle will join other scavengers like Ravens and Common Buzzards at a dead sheep or deer, dominating the smaller birds. With its superior strength, it can carry away portions of a carcass, occasionally up to 5kg. While live prey is more likely to be taken in the breeding season, carrion can dominate the diet in winter – this is probably due to availability, rather than any preference on the part of the eagle. Many upland birds forsake the hills for lower ground in winter, so prey choice for eagles staying put in the mountains becomes more limited.

This hunter takes most of its prey on the ground, usually after a surprise attack and perhaps a short chase. When hunting, it will often scan for prey from a high, soaring flight. It may then go straight for the attack or ‘stalk’ its intended victim by dropping down to use mountain ridges and other natural landscape features as cover. In this way it can remain hidden until close to its target. The pursuit that follows is likely to be short and sharp, as the eagle can easily keep pace with a darting hare or whirring grouse, unless there is some deep cover into which the prey can escape. The final pounce is a fast, powerful stoop on folded wings. A low-level, slow searching flight alongside hill ridges is often used without prior knowledge of the exact whereabouts of prey.

Golden Eagles also sometimes catch birds in flight with a long, fast stoop attack, striking their prey in mid-air and delivering a lethal blow with the talons. Eagles nesting close to the coastline will use this method to catch seabirds at cliff-side nesting colonies.

In some parts of its range, the Golden Eagle regularly tackles large and fleet-footed prey in the form of medium-sized grazing mammals. To accomplish this it needs a special hunting style and, often, an accomplice to help break a victim away from the fleeing herd. It is not unusual for a pair of eagles to co-operate in this way to secure a particularly large prey item. Once this is achieved, the attacking eagle will land on the prey’s head or neck and sink its talons in, ‘riding’ the running animal with wings spread for balance. Sooner or later the victim will drop, whether from exhaustion or injury, and the kill can be made.

Other hunting methods include sit-and-wait, where the bird chooses a perch and watches the ground below for prey activity, and what could be called ‘walk and seize’, where the eagle simply strides up to its prey and grabs it. This latter technique is employed to deal with large but relatively immobile prey, such as newborn deer fawns. With such a variety of tricks up its sleeve, it’s no wonder this predator’s prowess has impressed so many over the centuries.

In most nests, the older and stronger Golden Eagle chick will kill its younger sibling.

COURTSHIP AND REPRODUCTION

Golden Eagles are monogamous and pair for life. As they can be long-lived birds, pairs may remain together for 15 years or more, and they will occupy the same territory over that time. This investment in their territory and each other pays off with improved chances of breeding successfully, compared to inexperienced new pairs in new territories. Each pair’s territory lies within their home ranges, the total area within which they hunt – the difference is that the territory is defended against other eagles but the rest of the home range is not. Like many birds of prey, they need a larger area for hunting than they could ever hope to effectively defend against intruders.

The undulating display flight of a soliciting eagle is also used in aggressive territorial displays against intruding birds. Persistent intruders will be dived at, and if things get really heated defender and intruder may even lock talons and cartwheel groundwards. Both sexes will perform the undulating flight in response to an intruder. There is little obvious courtship between the members of an established pair – indeed, they are busy building or modifiying their nest from as early as autumn.

The nest is an often massive structure, as befits this mighty bird, built – usually on a suitable crag ledge or in a large tree – with a foundation of sturdy sticks. With trees not overabundant in many Golden Eagle areas, finding suitable sticks can be a lengthy process, perhaps explaining why the birds begin construction or renovation so early. The pair share stick-finding duties, while the female does the bulk of material-finding when the search is on for softer stuff to line the inner nest. As the nest nears completion, the pair mate frequently, and the first egg appears sometime in March or early April. Eggs appear at three- to five-day intervals but incubation begins immediately, so the chick that hatches from the first egg has a sizeable headstart over the rest. The completed clutch is likely to be of two eggs, though one and three are also common clutch sizes.

The small chicks will be brought meals of meat by their father and this will be torn up and carefully fed to them by their mother. At four weeks, the chick (there is probably just one left by this stage) starts to rip meat up on its own. Over the next 30 to 50 days it gains strength and grows its first set of feathers, then flies the nest. It will remain nearby for several more weeks, working on its flying skills, beginning to learn to hunt, but mostly waiting on a favourite perch for a food delivery from one or other parent. Independence is achieved gradually over a long period, and by the time the eaglet is truly out on its own and venturing away from its parents’ territory, winter is coming and there should be good supplies of carrion around to compensate for any shortcomings in its ability to take live prey. Youngsters may stay in or close to their parents’ home range well into late winter, but most will eventually go in search of a new home of their own.

SIBLING RIVALRY

Many young raptors behave badly towards their little brothers and sisters, but Golden Eagles and other related species take this to a shocking extreme. Most younger chicks will be violently killed by the first-born when they are just a week or two old, a phenomenon known as ‘Cainism’ after the murderous biblical figure. The considerable age difference between chicks one and two means the younger one has little hope of fending off the attacks. The behaviour seems to occur irrespective of how much food is being brought to the nest at the time, and the parents do nothing to try to stop it.

Why does this occur? And, given that it does occur so frequently, why does the female still usually lay two eggs? Perhaps the extra egg is there as ‘insurance’ against some disaster befalling the first egg. Another explanation is that when the local Golden Eagle population is low, the parents will have more time to spend caring for their brood rather than in territorial defence, and thus a higher chance of rearing both chicks. A further possibility is that the older chick will think twice about attacking the younger if there is a high risk of injury to itself, and the younger chick will be stronger and better able to defend itself if its mother was a well-fed female in good condition, able to produce two equally ‘good’ eggs. This would predict that Cainism happens more often in pairs that occupy generally less productive territories, and that is indeed what is observed.

MOVEMENTS AND MIGRATION

As we’ve seen, Golden Eagles show remarkable loyalty to their territories throughout the year, and while they may traverse a large home range in their daily foragings, more extensive movements are unusual in adult birds. Youngsters do wander sometimes considerable distances. Satellite-tracked young eagles have made exploratory flights of well over 100 miles in their first few years of life. They are