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Simon Thomsett on the African Crowned Eagle – Part 3

July 6th, 2011 · 7 Comments · Interviews

This is part 3 of Simon Thomsett’s writings about the Crowned Eagle. See here for part 1 and here for part 2.

Crowned Eagle pair with chick, © Simon Thomsett

Movements

To my knowledge no population of Crowned Eagles migrates, or has seasonal movements. One might expect juveniles to move after foraging parties and disperse widely, but not adults. They appear to be very sedentary, but appearances can be deceptive and further study may show unexpected swapping of spouses, hedge hopping, cuckoldry and large movements of some individuals. In the housing estates of Tai, urban lifestyles may be expected! Leslie Brown once noted an adult Crowned Eagle after a rain storm in Tsavo on a small and dry hill. It must have been on passage. I have seen an adult Crowned Eagle in a sparse river bed at Lewa Downs far from its usual habitat and assumed it was just passing through. None had visited the area for years, and none did so since, so it may have been on passage. Juveniles can appear in bizarre places, such as the Nairobi Golf Course near the city centre but this is not evidence to say that they are living there, and thus prospering (as was the suggestion).

Annual or Biannual reproduction
One might expect that the ‘forest’ eagle reproductive recruitment is higher than that of the ‘bush’ eagles because of greater competition and presumable greater risk of violent death. If better and more assured nutrition is a factor then again one would expect the ‘forest’ eagle to produce more. Unlike the ‘bush’ eagles they do not share their territory with Martial, Verreaux’s and African Hawk Eagles…but with each other. There is no greater a direct competitor than one’s own species. Their close proximity and the vicious engagements they must surely endure from neighbouring pairs means that it is likely that mortality from territorial combat is higher than with ‘bush’ eagles. The fact that the ‘forest’ eagle have a particular taste for adult male Red Colobus, the ignoramus bully with forearms longer than mine, also makes one ponder if they get wounded by prey more than the ‘bush’ eagles. Despite being later proved wrong when I caught a couple of recently fledged youngsters in Tai that looked like second year birds I kicked around an idea with Susanne and Guy Rondeau that they also matured quicker, because they had to. In a more violent world maturing quicker and breeding faster would be beneficial and perhaps it may happen. That one chick per annum has been recorded in similar South West Ugandan forests (which sent ripples of anxiety through Crowned Eagle lovers the world over) could be explained as a one off, premature death of previous chick, or that locations of endless and stable bounty could turn out more young. It may be one of those things that can occur in super-productive and perhaps more violent forests. Annual breeding for a species with so long a reproductive cycle must require great effort only possible or necessary in an area with food abundance and high mortality.
In captivity Crowned Eagles could breed each year and I have deliberately accelerated or delayed them by keeping their chick with the pair. A begging youngster is a definite libido crusher. Once removed (after at least 4 months) sexual activity quickly returns. Returning the chick once mating and nest building commenced saw the parents divided with the adult male being attentive and the adult female being aggressive. In this case the chick was a female, and so it could have been considered sexual competition. It is unwise to assume that the Crowned Eagle (or any other) is an obligatory biannual breeder irrespective of extraneous considerations. If the chick has dispersed or died earlier than usual there is nothing stopping pairs recycling in equatorial and tropical Africa. But I understand that there is enough evidence to suggest that the breeding cycle is too long for a usual, temperate world (South African) annual breeding cycle.

Hunting methods
I have had unique opportunity to watch Crowned Eagles hunting in trained and wild conditions. I have trained some 15 Crowned Eagles over the years, mostly captive bred, but some passage and haggard birds as well. I must have seen a few or more hundred kills, mostly hares and springhares (taken at night down a spotlight) and vervet monkeys during the day. The wild ‘taken’ (all rehabs) adult birds would, one must assume, replicate the same hunting methods they utilise in the wild if given the chance. I noted among their repertoire of techniques blind approaches to prey, using contour and tree trunks to hide their attack. Monkeys and hyrax feeding on limbs in full view causes the eagle to freeze and lengthen, until one walks with it behind an obstacle. Only then does the eagle flare its facial disc, crane its neck and show signs of intense excitement. When sure that all members of the prey are unable to see its approach it launches its attack straight at the individual most likely to be the greatest surprised. Whipping around the tree trunk at the last second it either connects with the prey, or sends the whole group into disarray and panic and misses. The extreme interest shown in prey that goes behind an obstacle is common with all Crowned Eagles, no matter their age or upbringing.
I had one female, Girl, a wild taken adult who would fly at a 45 degree angle from the fist directly over running Kirk’s Dik Dik, then plummet vertically down on them from as high as 10 to 20 metres. Her last second vertical approach was extremely fast and manoeuvrable, capable of spinning her around a bush. It had an almost 100% success rate whereas her captive bred offspring would simply tail chase and usually miss the same prey.
Recognising that any falconry-type hunt is poor evidence of methods used or prey species taken in the wild by wild eagles I shan’t document the methods used by the developing young, other than to say that hunting is learned, and they adopt some particular patterns as they mature. Young Crowned Eagles are particular poorly developed when it comes to recognising prey, and dissecting it. If captive bred birds are familiar at the nest only with a certain selection of whole prey they happily consume and dissect it when latter presented with them away from parental supervision. But if suddenly given a new species, such as a dead genet or Syke’s Monkey , they stare at it with confusion or even fear. Clearly parental choice delivered to the nest will be handed down to their young. Young eagles making their first few kills in captivity are inept to a degree seldom seen in other eagles. They bungle attempts, give up quickly, fail to anticipate avoiding action and often show fear. In killing they show a quick ability to learn which end is best to squeeze. Very soon, after a series of catastrophic mistakes and severe beatings they can subdue large prey by a head and shoulder grip. But once they have killed something they are keen to experiment and can be fool hardy. I suspect that they largest kills are taken by juveniles. This is the case with most raptors.

Mute, © Simonn Thomsett

I had better opportunity to witness these developing methods while hacking captive bred Crowned Eagles in Tsavo West, Mathew’s Range and Ol Donyo Laro over a ten year period. Nine chicks were born, hatched and raised with their parents Rosy and Girl at my home in Athi. They were usually removed at 4 months of age and then settled outside with a foster parent or older sibling to whom they sometimes associated and solicited food. Crowned Eagles are very easy to train but were never allowed to be tame and confiding of strangers as would most falconry birds. They were always managed to keep a reserve against people lest they not fear humans when wild. These trained eagles knew how to hunt at home taking hares, spring hares, mongoose, genets, Vervet Monkeys and much less often Thomson’s Gazelles and Black backed Jackal. The largest kills have been adult female Bush Buck and Impala, as well as their calves. They tail chased them then flattened them and a very basic and thuggish manner. The trained eagles were taken as ‘pairs’ for release and they profited enormously from being together. ‘Pair’ release is a method I would recommend for any re-introduction programme of large and socially complex raptors. They would hunt together, working a tree or bush until prey was flushed into the other’s path. This would often be by accident not design to start with then develop into a segregated task. After years of being together in the wild they would develop a working sympathy with each other that I was able to watch and not interfere. Usually the male would be ‘told’ to go in by the squeaking female. The female would sit high, look keenly at the prey beneath her and squeak and whine in a fever of over-dramatised intent. The male would appear to be driven to make the first courageous move, sometimes wriggling his way on foot in through dense thicket towards the hiding prey. She would reserve her pursuit and strike for the flushed animal, but as often make a mess of it by prematurely launching at the prey when she thought the male was within grasp.
Often one would land on top of a tree full of vervet monkeys. As they piled out of the tree the other (male usually) would take one on the way down or on the ground when running directly away. The level of co-operative hunting was unquestionably altruistic in that one would accept that it could not capture the prey, but serve only to flush it. Smaller prey was reserved for the male (such as female or juvenile vervet), larger (adult male Vervets) for the female. At all times the male would immediately relinquish prey he had caught to the female, even before it was dead although sometimes both would foot the prey especially if it was large enough to allow space.
None of these methods are unique for raptors. What emerged that only recently dawned on me as a probable ‘new’ hunting method worth publishing is as follows. What I witnessed was the quick and vicious attack on prey that appeared only to bowl it over and wound it. I had long ago been impressed by the ability of this eagle to seriously wound prey and leave it alone to die. In 1978 Rosy killed a Bushbuck female in circumstances I then did not think was normal. He hit the running female (only when it disappeared behind trees) that ended up upside down in a hedge. He hit it and was swung off it almost instantaneously. While deliberating what to do about the unfortunate Bushbuck, and worried about the fierce glare of Rosy in the tree above, it collapsed. I pulled it out while moribund to have Rosy violently push me aside and set about stabbing it along its entire length of neck. He then leapt back when it stretched to die. On PM I noted a huge subcutaneous bag of aerated blood, punctured rib cage and lungs as well as large haematomas on the neck. It had died of blood loss.
At a hack site at Finch Hattons Tsavo West a ½ grown bushbuck, always in close attendance with its mother, greatly excited one female eagle who followed it for 2 days. She made exploratory runs over it, to be thwarted by the mother turning to face her approach. On one occasion the eagle landed near the calf and the mother ran in and violently knocked the eagle away. The calf was inseparable, never leaving its mother’s side because of this attention. The bushbuck would associate more closely with Yellow Baboons, primates that these eagles had learnt to avoid. But wherever the Bushbucks went the female eagle followed. Suddenly the eagle tried a different approach and flew straight at the calf and knocked it over and continued on. The mother Bushbuck and attending baboons had no time to react as it was over in a flash. The eagle made no attempt to halt but flew and landed to watch the result. The calf, immediately got up and stayed by its mother with it ears hanging low. I found blood on the ground, and clearly the calf was badly wounded. The eagle then followed the calf relentlessly for two more days, showing evident curiosity (by raising its crown, craning its neck, standing on two feet, leaning forward and flying to different trees to keep them in view) every-time it lagged or stumbled. Finally the calf was unable to keep up with its mother and the eagle killed it. I did not see the kill, but arrived very soon afterwards to ascertain that the first impact had left a lethal wound that had gone septic and punctured the peritoneum making a large aerated subcutaneous lesion. I am sure the calf was unable to keep up and its mother had walked away and was unavailable to help. I saw a vervet monkey struck and left, in similar manner. It sat in a tree for hours, unable to keep up with its troop before it swayed and looked very sick. It was taken at near death when it offered no resistance about two hours after being attacked. The reason for so a long hind talon (measured at 10cm in one female and 9cm in two captives) is perhaps now evident. It is, as I liked to tell visitors to my eagles (making a few friends no doubt sigh with despair at its repetition here) “The largest killing implement on the African continent”!!! The needle tip, extraordinary length and incredulous strength of grip will, in an instant, puncture vital organs of any animal weighing under 50kg. To stab and move on would seem the stuff of undercover espionage agents armed with umbrellas, but it has the same effect. The two groves down the edges of the talon may harbour sepsis-causing bacteria if the caked blood and tissue clinging there is an indication. Like a Komodo Dragon the Crowned Eagle may have developed a “bite and retreat’ method of hunting. Even if sepsis is not the result, the effect of a deep stiletto dagger wound, followed by days of patient waiting is a very effective hunting method. It is a reptilian method not necessarily showing great intelligence that I believe is used by Crowned Eagles.
The vital organs lie close to the surface and surprisingly the heart is vulnerable to a relatively small puncture wound across a board range of body weights. For example, a mouse may have its heart 3-4mm under the skin. A rabbit, some 10 to 20 times heavier has a heart 10mm under the surface and an Impala some 25mm. A raptor with a 2.5cm hallux such as a Long Crested eagle, kills neither impala nor hares, but mice. So why the over-endowment? Perhaps it is because although the talons are long enough the eagle has too weak a grasp to puncture an impala’s chest. But a Crowned Eagle can extremely easily puncture an impala’s chest and break every rib within its span of foot simply by gripping it without the assistance of a fast contact speed.
The Crowned Eagle is an incredibly powerful eagle habitually killing as far I understand the largest prey of all eagles.

Crowned Eagle, © Simon Thomsett

Conservation of Crowned Eagles
Markus asks what should we do to conserve the Crowned Eagle. All matters of habitat change, water loss, declining food productivity is directly related to human population. While TIME magazine can attempt to dismiss the reality by saying we could all stand on Manhattan Island, if we all breathed in 500,000,000 would all fall into the ocean. There seems a reticence today to avoid broaching the subject of human over-population, whereas in the 1970s this was not so. I drove recently Kampala (Uganda) from Nairobi (Kenya) and saw (apart from kites) half a dozen raptors, 2 dead zorillas, and one live Reedbuck standing in an irrigated plantation. Apart from two small forests (each about 2km in extent) in Kenya, and 2 small forests (One 4.5km and anther 3km) in Uganda I saw nothing other than dense human populations, towns, shambas, Sugar Cane, towns, exotic plantations, towns, cereal crops, etc. The trip back covered some 1200km. Potentially the Rift Valley and lake basin, with super-fertile soils, varied topography and altitude, straddling the equator, should hold one of the greatest abundance of life found on the planet. And so it does, but it is mostly human. It unquestionably lies within the optimal core of former Crowned Eagle distribution in the sub-region. I doubt such a bio-impoverished or human dominated landscapes is what westerners expect to hear of a region as large as the British Isles lying in the heart of Africa. But similar rules apply elsewhere. Combine tremendous land fertility (such as the Ganges flood plain) with subsistence farmers and you tend to get biomass converted into people. It happens in India, Far East, Burma, Malaysia and sub-tropical Indo China, Latin America as well as Africa. Only high education and a new ethical world order on principled restraint to limit our full human population potential can intervene. But there is no indication that it will and there is certainly very few leaders who today would dare champion these matters.
In the Ethiopian bio-geographical zone, loss of net primary production between 1980 and 2000 is about 18%. “Moderate” desertification in Kenya stands at 64% and “severe” at 21% (1997) These percentages are expected to increase each decade and has already forced people from former high productive areas to drier marginal regions. Our urban and rural population is predicted to meet around 2050 with a total population in excess of 80 million. Unlike global predictions of a population plateau, ours still climbs off the chart at 45% angle, with no predicted stabilisation point. Wildlife is expected to parallel these changes with proportional declines. Education cannot be expected to catch up with the task and apparently nor can catastrophic examples of the folly of such action force change.
The accumulated effect of anthropomorphic factors appear to seal the fate of Crowned Eagles in our region; but is this applicable throughout Central and Western Africa? Most nations show similar trends and to expect different is to hope for a change in humans.

Given that people have repeatedly demonstrated their ability to exceed the holding capacity of the land to sustain them (as noted by Leslie Brown in the late 1970s), and given the lack of responsible leaders willing to address politically sensitive issues related to population control, it would be foolish to expect a long term future for Crowned Eagles. For the last few decades there is no question that protected areas have secured the Crowned Eagles and they continue to do so as long as they are allowed to remain.
If asked where financial resources should be spent in order to conserve Crowned Eagles I would roll out the standard (tailored for foundation) response. Namely stick to the buzz words of the day, “Create local capacity……… using Crowned Eagles as indicator species………securing environmental services through the conservation of water catchment areas………..working with marginalised communities to achieve………..Community based conservation projects………blah, blah, blah. Put one beer in me and I’d say what the heck, it’s all a waste of money because of the juggernaut of humanity. If you think that is bad, then put a lot of beers into my colleagues after the stand up show (conference) in which they enthused optimism and be prepared to gulp down much Prozac©, lest you feel a tad worried about the survival of your own children! There is a peculiar discrepancy between the personal thoughts of a conservationist, and their professional stance. There has to be otherwise they would be out of business. The business obliges optimistic outlooks and when none are obvious they may be invented. If only for a little while till humanity has a complete change of world order. Many projects must go ahead without a truly achievable end objective and this leads to an uncomfortable duplicity in the organisation/individuals concerned. Entering a project bereft of confidence is the sad lot of most conservationists in out part of the world.

Finally Markus asks “what was your most amazing experience with the Crowned Eagle?”

Once when I was a lad I was crawling on all fours through a forest path on the Amboni river near the Aberdares looking for what I hoped were Golden Cat tracks. All of a sudden the Robin Chats, Bul Buls, cicadas and all the animals went quite. The hush then turned to an avenue of alarm, from hornbill to monkey, from monkey to bird; and this onward rush of terror fled toward me! Stuck in a well trodden low tunnel I stared ahead down 100m of clear sun dappled view and was filled with primeval alarm. I knew a fast approaching predator was on its way and it was coming straight for me at a frightening pace. There ahead I saw her, golden eyes and silent, approaching at leopard height at unfathomable speed as steady as an approaching jet fighter. I distinctly recalled the fact that her wings were half closed and unmoving. I saw too the pattern of light and shadows flashing across her unblinking eyes. I stared enchanted, as must a man in front of a charging tiger, aware of the futility of action and mesmerised by the beauty of my attacker. I closed my eyes for the impact, heard a loud bang over my head, heard a sudden explosion of growling colobus monkeys and felt a light fall of twigs and leaves as well as the thump of air. She had punched her way through the brush above me. In that fleeting second before impact I noted a frown of disgust. I was not what she had hoped. If I had been I would have been dead.
I guess I had experienced a very rare thing. I was targeted as prey and she had launched her attack from a hidden and distant position. She had known all the paths, had heard my progress, perhaps seen other birds and animals note my presence. Undetected she had started an attack and had entered the tunnel at so fast a rate that she had no need to open her wings. She must have done that same path many times before.
I have been hurt badly by wild and captive Crowned Eagles, seen them kill enormous things, had them die after weeks of care in my arms, seen them hatch out of eggs and lived with them longer than any other relationship, human or animal. But that one simple thing is the most memorable.

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7 Comments so far ↓

  • david

    “The Crowned Eagle is an incredibly powerful eagle habitually killing as far I understand the largest prey of all eagles.”

    Probably… Its because other eagle doesn’t have an access to a large prey and Not because of incapable of killing large prey, large prey availability is very limited to some eagle specie. Crowned eagles learned to hunt these large prey like impalas, dulkiers etc.. and without enough weaponry to defend themselves they are easy picking for the eagle than small but elusive prey.

  • david

    http://www.aves.no/images/reiser/filippinene07/Philippine-Eagle_Mindanao07.jpg

    Harpy eagle, Crowned eagle are my fave eagles and the Great Philippine eagle- One of the strongest eagle in terms of lifting capability of large prey among forest eagles.

  • Warren Goodwin

    Simon,

    I have read all three parts of the Crowned Eagle Posting… Good reading!

    It’s good to get a perspective of the real situation in Africa regarding Crowned Eagles and Raptors in General.

    I have first hand experience from Zimbabwe, having spent most of my spare time in the Matobo Hills studying Raptors as part of the Black Eagle Survey.

    Within the National Park, all appears well, but just over the fence is heavily degraded Communual Land.

    Within the park, Black Eagles (and other large Raptors) have access to a relatively bountiful supply of Hyrax, however outside of the park, and on the boundaries there is heavy poaching of both Hyrax species, not so much for bushmeat, but for the making of karosses and curios for the tourist trade. A number of large tree species are also felled for carving, both in the communual areas and within the park.(White Seringa is the favourite)

    In the communual lands, those pairs of Black Eagles that remain have been forced to become prey generalists due to the degradation and competition, taking more reptiles and birds than their counterparts within the park .

    Anyway, enough about Black Eagles…

    There were only around 4 pairs of Crowned Eagles in the National Park in the 1990’s (Not sure of the latest figures)

    Crowned Eagles there are not adverse to ‘commandeering’ the nests of other Raptors, and I know of two African Hawk Eagle and One Fish Eagle nest that were taken over. (One of the African Hawk Eagle nests was in a Eucalypt directly above a fairly busy road.)

    Other nests were/are situated in Homalium dentatum and White Syringa (Kirkia accuminata) trees.

    The Prey base is mainly of both Hyrax species, with a few gamebirds and Water Monitors thrown in.I found only one Vervet Monkey skull under a nest in the Maleme Valley, and there have been no other records of Monkey prey remains from the Matobo hills since. (as far as I know)

    Other Crowned Eagle nests are known on the Eastern fringe of the hills, outside of Communual areas, however these are few and far between.(Ron Hartley had a study nest in this area)

    Anyway…I hope that this has provided a little more insight ….

    I now live in Australia and am involved in Raptor Rehabilitation here.

    Sometimes when I look at a second year Female Brown Goshawk, I have at the moment, I can almost see a Crowned Eagle…similar design and similar temprement in a much smaller package!

    Cheers,
    Warren Goodwin

  • martin wheeler

    Hi simon, thought you would be interested in knowing that I flew to the mathews end of june to pick up crowned that had injured right wing and starving its taken a while but she is standing and a bit more full of beans. Your write up is sensational and very inspirational. I have found one crowned eagle nest in the mokogodo forrest, chick is now 7 months old. Another in the ngare ndare but have not been recently to check, have also seen male hunting around laparua on lewa. Will follow up with e mail with more news from here. Cheers martin

  • Nicu Parlog

    Awesonme, high class informations about the most formidable eagle species. Thank you!
    Based on your experiences and info relating these rpators, you should write a book about them. The first monography about african crowned eagles. Seriously!
    Regards

  • Steve Bergh

    Simon. Finally had time to sit and read part 3. Great insights.

    We have no over population issues in Alaska and Gyr s perigrines and Golden Eagle doing extremely well here. The habitat is not endangered and very isolated. This is one of the draws for me to move here may years ago. The USFW have documented the porcupine Caribou herd to unimaginable levels. The oil on the north slope has facilities the ability to study this migrating deer more than any other herd in the world in terms of dollars. The animal that kills more Caribou on the north slope of Alaska is the Golden Eagle. They kill more caribou that grizzly bears, wolves, wolverine, combined. Pretty incredible if you think about it.

    My observations concurs the stupidity of young raptors in the learning process of hunting skills. I had a Gyr falcon bind to a white tail buck and ride it to the wood before finally letting go. I had a perigrines on it first flight at ducks put in a full blown stoop from a good pitch. I was looking averywhere for what he was diving at and there was nothing in the air. He continued his plummet to earth in my amazement and went straight into a pond and as he hit the water I watched a drake mallard side swim as he splashed into the water and then watched the duck fly casually off. He swam to the waters edge soaking wet for me to pick him up. This may be why the mortality rates are so high with eyass’s.

    Have you tried to stretch out egg production on the captive breeders you have? It sounds like you are allowing them to incubate their own eggs. I had a female perigrines that would lay and if you continued to pull the eggs out from under her she would continue to lay. I was cooking them in a incubator so when I wanted her to stop I put in some dummy wood eggs and she would stop laying and start incubating. It is my understanding the Crowned lay 2 eggs and the Cain and Able syndrome takes place. Can egg production be extended for production reasons and,incubate the eggs? Do you have foster rearing capabilities for the other young? I had a pair of natural breeding Harris hawks that would rear anything put at them. Great parents and have heard Harris Hawks do this in multiple other situations for other breeders. Easy to keep birds and the most emotionally stable birds I have ever seen.

    Keep up the good work. I would love to spend some time at a hack site of your some day.

  • Jacques Sellschop

    These articles reveal an exquisite blend of emotive passion and scientifice objectivity wrapped up in monumental dedication. I have spent several months observing and photographing a breeding pair of Crowned Eagles that, for the past 9 years, have been resident on the upmarket San Lameer Golf Estate 140 kms south of Durban. Abundance of food (hyrax,vervey monkey,red and blue duiker and various birds) appears to have led to annual reproduction for the past 4 years. In April 2012 the nine-year nest 90 feet up in a Pine tree mysteriously disappeared. On 27 July this year the pair started rebuilding from scratch in the same tree about 1 meter above the position of the previous nest. Some four weeks later the new nest appears virtually complete and is currently being lined with pine needles by the pair which I have photographed mating on and near the nest. The 10-month-old juvenile hatched last year frequents low, indigenous trees bordering the 17th fairway about 300 meters from the nest and still yells regularly for room service. I have photographed it tugging at bright red, meter-long metal fairway marker pipes 3.5 cms in diameter , sunk into the ground for a third of their length, until it has loosened them sufficiently and then plucking them out of the ground before flying into nearby trees with the toys. A rare photographic moment occurred when the adult female was feeding the 3-month-old juvenile a vervet monkey on the nest. Mother had dismembered a monkey arm and holding it by the elbow, offered it to the youngster, hand-first. Inadvertently she held the disembodied arm by the digital flexor and as the juvenile took the monkey’s limb, the dead hand closed tightly over its beak. The sequence of five pictures I took shows the immense surprise both birds manifested at this cheeky gesture by the corpse. I will be happy to share pix with anyone interested in the San Lameer eagles. Email me at: mwsellsc_j@mweb.co.za

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