Shandon Estate's Crowned Eagles:  Final Report

May 2020

Dr Garth Batchelor, Peter Retief and Petri Viljoen

Shandon Estate / Shandon Eco Reserve kindly allowed a remote camera to be placed next to a Crowned eagle nest last year to record the breeding biology of the pair of eagles. The camera was solar powered and connected remotely to a computer so that the eagles would not be disturbed. The camera was put up in February long before egg laying (25 August) so as not to cause any interference with the eagles.

The camera worked perfectly until 10 January when it suddenly stopped on 10 January 2020. We were only able to fix the problem on 14 February 2020 so were not able to record images for a month (Fig. 1 & 2). Although this is regrettable, the chick did survive and we were able to collect further data for another 6 weeks after this period even after the chick had fledged and was free flying. The camera was shifted by a vervet monkey on 30 March 2020, stopping further images of the nest.

This is the final report for the 2019 - 2020 breeding season and the report covers the period 10 December 2019 to 30 March 2020.

Timeline 30 March 2019 to 30 March 2020

During the previous breeding season (1918/19), it was suspected that the chick had been killed and eaten by a baboon as broken feathers had been found below the nest and a baboon had been photographed coming down the tree on a camera trap the day the chick disappeared. A baboon troop was often seen in the vicinity of the nest this past season and it was feared that the old male baboon would again try to catch the chick. It was almost not a surprise then that when the nest was visited on 22 January 2020, there was no sign of the chick on or nearby the nest. I had heard baboons alarming as I approached the hide and suspected immediately that they had been investigating the Crowned Eagle nest. An immediate search was carried out by Shandon staff and myself but there was no trace of the chick or an adult eagle. With the remote camera, sadly, out of order after having working magnificently up till then, we had no idea of what had occurred. However, to our great relief, at 15h00 on Sunday afternoon when the General Manager again went down to the hide, the chick had returned to the nest, safe and sound. This was suspected to be the young Crowned Eagle's maiden flight. The young eagle was absent from the nest for at least a day and a night. The chick was 101 days old and younger than any record for a Crowned eagle chick leaving its nest under usual conditions. The fledging period is recorded to be about 105 days for male chicks and 110 - 115 days for female chicks.  According to the literature and personal experience, male chicks fledge earlier than female chicks which are quite a bit bigger. This chick appears to be a female as it was approximately the same size as the female Crowned Eagle when it fledged.  Unfortunately, the exact fledging date could not be determined because of the camera malfunctioning.

What was noticeable over the past three months is how seldom the male Crowned Eagle came to the nest. The male and female were only documented on the nest together three occasions, on the 12, 15 and on 24 December when the chick was still comparatively small. It is generally accepted that the male does most of the hunting when the chick is young while the female assists the male when the chick can be left alone on the nest. This pattern was noted in this study. On two occasions, two small impala legs were delivered to the nest on one day, on 21 and 30 December. It is suspected that both the male and female Crowned Eagles may also have brought in prey on these occasions. In both instances one of the limbs disappeared off the nest and is presumed to have been fed on by an adult eagle or else stashed for later use. Antelope were always quartered, and never recorded entire on the nest. Vervet monkeys formed an important part of the diet of the Crowned Eagle chick.  All the monkeys delivered to the nest were either infants or sub-adults (Fig. 4). Three Vervet monkeys were recorded being brought to the nest in total and one was fed on for 7 days until only a clean spinal cord remained. The bones were pecked clean of all traces of muscle and sinew by the chick. It would appear that small antelope, such as young impala, are also fed on for a number of days. After fledging, studies have shown that the chick remains dependent on its parents for food for up to 12 months until it can hunt efficiently itself.

Fresh leaves were brought to the nest at regular intervals by the female Crowned Eagle during the last quarter (Fig. 5). A fresh spray of leaves was brought to the nest on average about every 5 days during December and January. During February and March leaves were not recorded being brought to the nest. The species of trees from which the leaves were collected could not always identified although on one occasion a Cussonia spicata leaf was placed on the nest.

As expected, as the chick grew, and its feathers and muscles developed it spent more time exercising. It first started flapping its wings for short intervals on 27 of December then regularly flapped thereafter, increasing in "gusto" and time and in the end jumping up and down while flapping (Fig. 6), and eventually moving off the nest (Fig. 7).

On 24 December, the male Crowned Eagle delivered a monkey to the female Crowned Eagle on the nest at 12h05. She fed the chick for about half an hour then flew off with the monkey presumably to feed herself. The chick appears to be surprised as it can be seen calling after her as she departed!  (Fig. 8). At 16h34 she returned to the nest with the remains of the monkey and continued to feed the chick until 17h34. It is interesting that she flew away with the prey as in other instances the female eagle merely feeds on the nest with the chick. The next day, again she took the remains of the monkey carcass away to feed on and again returned later (17h34) with the prey remains to feed the chick (Fig. 9).

A behaviour not previously witnessed was that of the chick mantling over the prey. This behaviour is typical of the female Crowned Eagle when she collects prey from the male after it has been placed on the nest. The chick only displayed this behaviour twice, on 8 March and again on 10 March after a vervet monkey had been brought to the nest. (Fig. 10). 

A sequence of images taken by the Raspberry Pi camera are interesting in that it shows the apparent contempt with which vervet monkeys relate to a Crowned Eagle chick. A vervet monkey carcass had been delivered to the nest on 28 March and fed off until the next day by the young eagle. On 30 March a monkey sat on the camera overlooking the nest and chased the chick off the nest and shifting the alignment of the camera!

Over the breeding cycle a number of interesting aspects of the Crowned Eagle breeding behaviour have been documented. These include:

1. The pair bond is already strong in April long before egg laying. The process of refurbishing the nest starts early in autumn accompanied by impressive displays both on the nest and in the air.
2. Only the female Crowned Eagle was recorded incubating the eggs. The eggs hatched after 52 - 53 days' incubation.
3. The female eagle is aggressive towards the male when he brings prey to the nest, cowering her head and calling. The male in contrast appears apprehensive and cautious on the nest.  The male was never recorded feeding the chick.
4. Both the female eagle and chick mantled over prey
5. Fresh leaves were frequently brought into the nest.
6. After the first month, as the chick developed, the male eagle seldom came to the nest to deliver prey.
7. The chick appears to have been chased off the nest for its first flight after 101 days by baboons.
8. The chick returned to feed, exercise and sleep on the nest after being chased off the nest by presumably a baboon. 

Acknowledgements

We, Garth Batchelor, Peter Retief and Petri Viljoen would like to thank the management of Shandon Estate very much for affording us the opportunity and support in placing the remote Raspberry Pi camera and to record the breeding behaviour of this pair of Crowned Eagles over the past summer. The data gathered has contributed greatly to our knowledge of the breeding of Crowned Eagles.

Fig 1. John Davies climbing rope to repair camera.

Fig. 2. Tree top repairs.

Fig. 3. Male Crowned Eagle delivering prey.

Fig. 4. Male Crowned Eagle delivering monkey.

Fig. 5. Female Crowned eagle bringing fresh leaves.

Fig. 6. Chick exercising wings.

Fig. 7. Chick off nest.

Fig. 8. Female Crowned eagle mantling over prey.

Fig. 9. Chick mantling over prey.

Fig. 10. Evidence of culprit! Monkey's tail in front of the camera lens.

Shandon's Crowned Eagles:  Blog 2

12 December 2019

Dr Garth Batchelor, Peter Retief and Petri Viljoen

Blog 1 summary:

•  Raspberry Pi computer installation February 2019
• 2 eggs noted on nest 2 September
• Incubation 53/54 days
• Chicks hatched on Saturday 12 October.

Two chicks were recorded on the nest initially but a week later only one was present. Eagles have a peculiar behaviour in that in many species where two eggs are laid, the strongest chick will usually kill or injure the second chick to the extent that it dies. This is known as sibling aggression or infanticide.  The Cain and Abel behaviour is known to occur in Crowned Eagles and it was hoped to document this with the remote camera. The images recorded from the camera were unable to detect this aggressive behaviour due to the deepness of the nest cup. However, this practice of sibling aggression and infanticide has been documented for other eagle species including Verreauxs', Wahlberg's and Martial Eagles. The first chick to hatch is usually the chick that survives. It is presumed to be an insurance policy should one of the eggs be infertile or a chick being deformed.

The Crowned Eagle chicks, as with most other eagle chicks, are also covered in white down on hatching.  They remained covered in snow white down until their wing feathers start to erupt 40 days. These feathers are grey or black in sharp contrast to the white. The quills for the secondary and primary feathers on the wings were first noticed on 21 November 2019. Soon after, the dark feathers on the back started appearing.  

It was noted that while the chick was very small, the female Crowned Eagle used to collect a spray of green leaves, often from a round-leafed kiaat, (Pterocarpus rotundifolius), or a mingerhout, (Breonadia salicifolia), and place it on the nest. Later as the chick got larger she would bring in a spray of leaves at any time during the day but less frequently. The purpose of bringing in fresh foliage is not known but it is thought to be related to nest hygiene. The leaves appear to cover over old prey. On other nests, leaves from a number of different species have been recorded. These are often aromatic for example pine needles and Eucaluptus spp. The leaves of white syringa, Kirkia wilmsii and kiepersol , Cussonia spicata have also been recorded.

When the chick was small and defenseless the female Crowned Eagle remained on the nest or on a branch in the nest tree for most of the time.  She spent the night on the nest with the chick. As the chick became stronger and able to move around the nest, the female spent more and more time away. She no longer slept on the nest. On very hot days, even when the chick was over a month old, she would return to the nest and mantle over it to help keep it from overheating. She herself became extremely hot and could be seen to be gular panting, with her beak wide open. Birds, being covered in feathers, which are extremely efficient insulars against heat loss, cool down through gular panting. This is even more important in eagles whose entire legs are feathered unlike other birds. The female eagle also returned to the nest during storms and heavy rain to protect the chick from becoming chilled. She appeared almost saturated after heavy rain events. The chick still being covered mostly by down would have been very vulnerable to chilling should the female not have protected it, feathers being more waterproof than down.

The images from the Raspberry Pi camera showed that the male eagle continued to deliver prey to the nest after the eggs hatched even when the chicks were very small. On arrival to the nest with prey, the female eagle would rush up to him, collect the prey from his talons in her beak and then mantle over it. He would then depart.  Sometimes he would sit on a nearby branch in the nest tree or else fly directly off. Most of the prey was delivered in the morning usually after 10h00 although this was not always the case. On the 16 October 2019 the male delivered prey at 06h51 while on 30 November 2019 he delivered prey at 16h14.

Initially during incubation the female eagle would sometimes leave the nest for short periods. The male eagle delivered a number of items of prey during this time. In all only 8 deliveries were recorded. Most of the prey was small mammals. Amongst these, Greater Bushbabies were recorded and an antelope leg. On a number of occasions she would leave the nest for short intervals and it is assumed that she went off to feed on prey which had been delivered by the male.  An assortment of prey items have been recorded on the nest to date, these include Water Mongoose, Greater -spotted Genet, Grey Duiker, Red Duiker, Impala fawns and Vervet Monkeys.

It is not only the Crowned Eagles who have been seen at the nest. Cape Glossy Starlings have been recorded at the nest a few times. Initially it was thought that they were coming to collect scraps of meat from the nest.  Although this is possible, a starling was seen collecting a piece of eagle down from the nest for its own nesting material. I have also recorded Grey-headed Sparrows collecting down off another Crowned Eagle nest.

Some amazing images have been recorded by the Raspberry Pi camera of the female Crowned Eagle and the chick during extreme weather events. A severe storm came in from the south on the evening of the 23 November. At 18h11 the storm hit the valley accompanied by strong winds and rain. It is amazing the nest did not blow out of the tree!    

On 30 November, the temperature soared to 39C . Images show both the chick and the female eagle gular panting  and the chick being sheltered from the heat by the female. Her dark charcoal plumage on her back may camouflage her in dappled shade but would not bring relief from the sun! From the 9 to 12 December the Lowveld experienced a period of cold weather with almost continuous rain. Both the chick exposed on the nest and the female eagle sitting on a nearby branch became saturated. The chicks down clung to its body and it became stained brown from the nest and nest contents. While watching, it from the hide on 10 December its continual shivering was clearly visible.

 Two week old white downy chick

 Female Crowned eagle gular panting during exceptionally hot weather

 Female Crowned Eagle shading chick in hot weather 

 Starling collecting eagle down (Image  G.R. Batchelor)

Six week old chick showing emerging primary and secondary feathers on wings (Image G.R. Batchelor)

Crowned Eagle being blown about on nest during a storm

2019.05.17 Pre-laying  courtship behaviour of Crowned Eagles on nest. (Female on left).

191015 11h52 Female Crowned Eagle delivering fresh leaves to nest with two,  1 day old eaglets.

20190507 10h59 . Pre-laying  courtship behaviour of Crowned Eagles on nest.  (Female on left).

20190508 10h50 Pre-laying  courtship behaviour of Crowned Eagles on nest. (Female on left). 

190726 14h14 Courtship feeding, Male Crowned Eagle delivering prey to female Crowned Eagle . Prey unidentified.

190708 13h34 Male, wings raised, female courtsey display behaviour.

190826 10h09 Female Crowned Eagle inspecting newly laid egg.

191008 10h50 Female Crowned eagle collecting head of Red Duiker from male Eagle. The image was lightened to show the head of the duiker.

20130911 An immature Crowned Eagle flying fledged from the Municipal Nature Reserve nest flying over Shandon Estate.

192029 06h51 Crowned Eagle female with 15 day old chick

Background

For the past twelve years the Crowned Eagles around Nelspruit/Mbombela have been studied. The focus of the study has been on determining the population density and whether the population is a source or a sink. In other words, is their population a stable one producing a surplus of chicks or is the population shrinking. To date the information obtained from monitoring the nests tends to indicate that the population is healthy, producing  a surplus of chicks. The known nests are used regularly, usually every alternative year, or annually if they have a breeding failure. 

The pair of Crowned Eagles that now nest on Shandon Estate used a nest in the municipal nature reserve for a number of years. Their nest was first discovered in 2007 and was already a massive structure so had obviously been used  for many years previously.  This nest was abandoned in 2011 and they moved onto the Shandon Estate in 2012. This pair of eagles is unique in that it is the only pair being monitored that has attempted to breed every year since their nest was discovered. Most pairs breed every second year. The reason for breeding annually is not known  as they have had chicks annually and at least two have successfully fledged.  The presence of a fledged chick  is thought to inhibit the urge to breed during the year after fledging as it still needs to be fed for as much as ten months after fledging. This is similar to the Martial Eagle which also breeds every alternative year. A possible reason why this pair breeds every year is that the chick is not surviving.  This was confirmed during  the 2018 breeding season when  in December, the three quarter grown chick was suspected to have been killed by a Baboon on the nest.  Quilled feathers from the chick's wings were found below the nest. A male Baboon had been observed sitting near to the nest just two days earlier.  It is possible that baboons have also been responsible for other chicks not surviving and this being the reason why this pair of eagles breed every year. 

In order to test this theory, a proposal was put to the Shandon Estate management to install a remote recording camera at the nest.  With the guidance of Peter Retief, a local computer specialist, a sophisticated remote miniature computer called a Raspberry Pi and attached small camera, has been placed near the nest to try to record the breeding activities of the eagles on a continual basis for an entire breeding season.  The camera and its accessories were funded by the owners of Shandon Estate.  The camera was installed in March, long before the commencement of any nesting activities,  so not to disturb the eagles. The camera was placed in the tree over twenty metres up by John Davies from the Endangered Wildlife Trust. It  has already taken some amazing images of the pair of Crowned Eagles on their nest. The advantage of this camera is that it can be programmed to take images as programmed by the computer from Peter's desk! He can also observe the images being taken from his office without disturbing the eagles. This is the first time this technology has been used in South Africa to document bird nesting behaviour.

Discussion

The Raspberry Pi camera has been recording images daily now for seven months without a hitch. A number of very interesting images have been recorded during this period documenting behaviour  patterns not previously recorded such as  pair bonding and also the breeding behaviour of the eagles on the nest.  The camera allowed us to determine when the eggs were laid even though we could not actually see them. It also allowed us to determine the exact day of hatching from recording the behaviour of the eagles.  The eggs took 51 days to hatch. The "Cain and Abel"  battle where one chick succumbs to the pecking by its sibling, was unfortunately not documented clearly due to the depth of the cup in the nest. The surviving chick is now two weeks old. Where possible, prey items are being identified. So far greater bushbabies, red duiker, rusty spotted genet and dwarf mongoose have been brought to the nest.  If all goes well, the chick will start leaving the nest in about 90 days time! 

Acknowledgements

Peter Retief for developing and programming the Raspberry Pi  computer and camera and his endless enthusiasm of the project, Petri Viljoen for initiating the project, Jaco Badenhorst, the General Manager of the Shandon Estates for his continued enthusiasm for the project and all property owners who have contributed towards this unique project in various ways.

Garth Batchelor