THE URBAN CROWNED EAGLE
This blog follows experiences and events throughout the course of my research while based at the University of KwaZulu-Natal.
This MSc research is focusing on the ecology of urban Crowned Eagles. How do they survive, even thrive, amongst the urban environments of Durban and Pietermaritzburg, South Africa?
On the 27th of November the Victoria Country Club nest camera was serviced, replacing 12 batteries and collecting the data - 9,400 images over the course of 23 days of operation.
There are just too many fantastic images it is overwhelming. So here is just one day showing the full suite of images taken from that day, period of interest have been slowed down to appreciate these great images.
At just 12 days old, the Angazi (yet to be named) crowned eagle chick is thriving and doing so well. We are planning to service the camera again next week for another batch of 10k images!
I knew very early on in the season that Egyptian Geese had an interest in the Zimbali crowned eagle nest. On the 25th of September, even while the eagles were incubating, I observed a pair of geese flying up to branches on the underside of the nest, at first I thought they were trying to steal nesting material, but they were probably trying to steal the entire nest. Fortunately the female eagle sat strong and steady and the geese backed off. I have no record of the geese interactions during the incubation period and the first 20 days of chick rearing, I only suppose that the eagles were very forceful or the geese wisely cautious. And during the months after the camera was installed, while the young eagle was flightless and sedentary on the nest, there were no incidents observed. On the 18th of December the eagle chick was ringed with a yellow N2 band, she was measured as a large female and returned to the nest. N2 fledged at about 115 days of age around the 26th of January.
After fledging, young crowned eagles are still completely reliant on the adults for delivering food, and unlike many other raptors which will chase and steal prey from the incoming adults crowned eagle fledglings wait courteously on the nest for the food to be served. This can go on for five months post-fledging and so my diet studies using the cameras continue for months after.
I timed my next camera service once the young eagle had made its first flight, and didn't notice anything unusual - unknown to me at the time was that the first few eggs of the clutch were deceptively hidden, covered by the detritus of nesting material . On the next camera maintenance visit three weeks later the goose nest was obvious, lined with goose down, and again the eggs were deceptively covered. I got a hell of a fright when one of the geese swooped past me and landed on the nest hissing with fury - I thought it was one of the eagles! I laughed as the adrenaline rush of fear gave way to amused chagrin at the silly goose.
Silly goose on the left !
In any case – the camera was kept operating to see what would happen at this peculiar situation, and Zimbali has been a thrilling data-set to analyse both because of an exceptional diversity of prey remains, and this peculiar interaction between geese and eagles.
One would think that the eagles would simple dominate here, overpowering, even killing the geese right there on the nest site. Recent Black Sparrowhawk research revealed that geese overpowered and usurped sparrowhawks, but the interaction between this particular eagle and goose duo has been somewhat of an example of commensalism. In ecology, commensalism is a class of relationship between two organisms where one organism benefits without affecting the other- derived from the latin commensalis, meaning 'sharing a table'.
A summary of the situation – which I hope to describe in more detail on a journal note (so take heed of the copyright and intellectual property statement at the footer to the blog), is:
On the 28th of January, just a few days after the young N2 fledged, the goose first visits the nest and digs a goose-sized divot in the rotting nest lining. The first egg is laid on the 2nd of Feb and is subsequently kicked out - a full clutch of 7 eggs is laid by the 8th.
During the early stages of incubation the eggs are left covered and concealed for long periods while the eagles continued to deliver food, and the juvenile continued to eat casually on the nest. I am utterly shocked at how long these eggs can go without being brooded – and during data analysis held little hope for the success of this clutch of geese. Even up until the 10th of Feb N2 slept the night on the nest. For the next few weeks the nest is shared between eagle feeding and geese brooding.
By the latter weeks in February the antagonism becomes clearer, maybe the geese eggs require far more attentiveness in order to ensure the survival of the duck embryos. So while the adult eagles still drop prey at the nest, it appears that the geese throw them out. Zimbali visitors have had wonderful experiences with the trusting N2 while she had to eat her meals on the forest floor.
Floor food, a Blue Duiker leg. Photo by Benine Du Toit
The clutch of eggs were last seen on the evening 12th of March, and even on this day N2 had a nice feast of cane rat on the nest. By the morning of the 13th, the brooding behavior of the goose had noticeably changed – she now held her wings dropped – the eggs had probably hatched during the night, and the first glimpse of ducklings are seen shortly before 10am. She keeps a very close watch over her brood and only leaves the nest once, very briefly, that evening. The next morning, just 24 hours after hatching, its time to scarper before the little ducklings become eagle snacks. At 6.42am the mother goose guides her little brood off the nest. They jump and parachute 25 meters to the ground!
N2 received another meal from her parents at midday, and after eating her fill, she curiously crushed the hollow half-shells left in the nest. Another month of camera monitoring until the 8th of April revealed no further trace of a goosey interest. N2 continued to receive meals, and consume them in peace on the nest. The most recent photos were taken of a happy and healthy 'Miss Zimbali' on the 26th of May, and so it seems, life goes on!
Miss Zimbali as she is affectionately known by Adele Kieser (photographer)
Recently back from a fourth trip to Mkambati. This was set to be a very important one for Morgans [link] research on the Cape Vulture breeding colony at Mkambati Nature Reserve. It was a fantastic achievement of coordination and collaboration as Morgan brought together twelve people to take part in this operation. A thorough range of experts and assistants came together, including the Endangered Wildlife Trust’s Vulture Working Group, EWT’s Wildlife & Energy Program, Ezemvelo KZN Wildlife’s Bearded Vulture Research, The African Bird of Prey Sanctuary, Eastern Cape Parks and Tourism Agency, and KZN bird ringers and University of KwaZulu-Natal researchers.
The goal was to achieve a successful ‘mass capture’ of vultures in a walk in trap. With four satellite GPS trackers, and forty wing tags to attach, we were aiming to capture as many as the two teams could safely process without undue stress to the vultures. A hide is placed near the trap to observe and close the trap when a number of birds are inside. There was just enough room for three people, who would set up before dawn and sit until the vultures were caught. The remaining team was to sit a few minutes drive away, at a viewpoint over the ‘superbowl’ lookout, and wait patiently by for the call of all hands on deck.
Our previous capture back in November went surprisingly quickly. With ten birds caught within the first half hour, and all done and dusted by 11am that day. So expectations were high… “no we wont need to pack lunch” was one memorable quote uttered on the night of our briefing. On the first morning while we all waited at the wonderful panoramic scene at the superbowl, Juan Morgan and Ben sat for almost ten hours in the hide without the least hint of enthusiasm from the vultures. It was a long and frustrating day. By 4pm the vultures are less keen to feed as they are to get home to the roosting cliffs, and our stomachs lead us back to the lodge for supper.
Things got even more frustrating on the second day when, although vultures were feeding on parts of the carcass nearby, they were obviously very skittish, and never settled for long enough to be caught. Long days at the superbowl were passed in various ways: I was reading… a lot, Meyrick had a near run-in with a magnificent specimen of a Black Mamba while out walking, Kerin found a stunning diversity of wildflowers to identify, and Eva went off hunting for the Mamba that Meyrick was all too happy to never see again – only to return from a foray down the cliff with a picture of a porcupine, and a rather smelly skull of a red hartebeest.
Another nine hour day on the third day and despondency was setting in, particularly because for most of the day several vultures sat perched on top of the trap! The wind has been gusting for several days. Some clear signs of cabin fever were becoming apparent and we had accumulated something to the order of 33 person days of effort and still not one vulture to show for it. Something had to change.
That evening another carcass was procured, and the vulture restaurant was baited with fresher more enticing food. Day four was my chance to be one of the three in the hide, and that night I packed books and entertainment to keep me occupied for a bum-numbing ten hour watch. Arriving at the hide at dawn, the weather had changed, and the wind was barely whispering. I was hopeful, but nonetheless settled into the camp chair as best I could.
The dawn lifted, the wind had died to a whisper, white-naped ravens started amassing, and then a fish-eagle arrived. Within 20 minutes the first vultures landed by the carcass and started feeding in and mobbing in their raucous manner. The fish-eagle was first to be pushed off as dozens and dozens of vultures frenzied. The first-eagle was the first to notice the other carcass and move off towards the trap, followed by the late coming vultures who couldn’t find a place at the table.
Twenty-five vultures and a fish-eagle were caught within the first 40 minutes of the forth day. By 11am all the vultures were processed. There are now an additional four GPS tagged birds, and 25 wing tagged birds. These tagged birds will be invaluable additions to research on foraging behaviour, and nesting colony behaviour respectively.
arriving at Mkimbati Gate on the evening of the 13th
pre-dawn and ready to head out from riverside lodge
beautiful ocean sunrises each morning as we set out to the capture site
high spirits at the superbowl
our perspective of the trap from the superbowl lookout
the highlight of the day... LUNCHTIME!!!
frustration watching several hundred vultures pass by
on the dawn of the forth morning the fish-eagle takes the lead
25 vultures penned
the vulture team
ready to work. Photo by Kerin Bowker
removing a vulture from the pen. Photo by Kerin Bowker
many hands make light work. Photo by Kerin Bowker
heading home on the 18th, we spotted this pre-migratory congregation of Amur Falcons
After such an amazing month of fieldwork through the summer solstice, the pace and focus has changed dramatically. If there is ever a time to be office bound than the Pietermaritzburg summer isnt such a bad time. My office remains in the cool 20's while its a humid 34 degrees (or more) outside.
I have been wading knee deep in literature and reference material while attempting to write my introductory chapters. And this is set to continue for a few more weeks yet. This project has turned my attention to urban ecology. And moreso, the significance of urban wildlife as a source for the majority of the human-wildlife experience - as of 2008 more than half of the seven billion people on earth are urbanites.
The most highly modified places, the urban core is such an unfamiliar place for wildlife. The concrete jungle, tarred and sealed surfaces, and buildings of brick and glass - yet pigeons and peregrines have no trouble making use of these human made analogs to their natural cliff habitats. There are just a small range of these urban exploiting species, but they can occur in great numbers.
Towards the suburban and peri-urban areas the structures decrease and the landscape is tending towards a mosaic of green-spaces (parks, reserves and buffers) and residential areas with gardens trees and lawns. Much more acceptable for animals of more typical forest and woodland areas, and these areas have the riches variety of urban adapting species.
Hazards abound in the form of speeding vehicles, electrical networks, fences and of course people. It is actually surprising at how many species are able to adapt to urban environments, and Durban is blessed with variety. Thats for sure.
As the biology of the Crowned Eagle is viewed through the lens of urban ecology, there is much to consider about the eagles impacts and effects on the local communities; both wildlife and human. And I am now looking at a number of complex interrelationships, predator and prey, the preys prey, disease transmission, and human dimensions of percieved relationships. A few species thriving in the urban areas, hadeda ibis, dassies, and monkeys to name a hattrick of eagle favorites All have their particular conflict issues. Hadeda's are those flying vuvuzela's, forming rowdy roosts, and picking open garbage bags on collection day. Dassies, well those little rock rabbits are apparently pretty benign, I dont hear people complain about dassies. They seems to do well, forming colonies in storm drains, culverts, and rock banks. But monkeys...
Monkeys...
Monkeys tend to polarize communities. Their intelligence and character can work in their favour, but their ability to use that intelligence for mischief is the origin of a lot of animosity.
I like monkeys, they are inquisitive and adaptable, and they provide valuable protien for the most magnificent predator around here. But I have also been the victim of monkey burglary. And I have a particular sore memory of having a delicious moist christmas cake, prepared as a thankyou gift for our December house-sitting in westville, devoured in minutes, right there on the kitchen bench, while Patrick and I were watching our eagle trap out in the lounge. Cheeky sods.
Before I harp on about what they do, and what they dont do. I would just say that I was doing a web search for more information on issues around 'the urban monkey'. I found this. I haven't had a chance to watch the series but the trailer gives you an idea of some of these urban wildlife conflict issues.
First and most importantly being a new laptop!!! With 250,000 nest camera photos, in folders of 10k images each, the strain on RAM and graphics is demanding. The Acer netbook is going on four years old, and while compact it seriously struggles to keep up with timelapse analysis.
So I walked in to the store with my harddrive full of photos. Plugging it in and sampling their abilities of the various units. I managed to hang an Apple Macbook pro with my first trial. Then went to the PC laptops, and along to the end of the shelf, where the Samsung behemoth sat proudly beside its spec label... and pricetag. Eesh.
But it was barely started, still in the process of installing Chrome, Skype, Googel Earth, and other useful apps, when I discovered the Movie Maker. A quick exploration with two sequences I was familiar with and I came up with these results. Pretty happy! Animated sequences like this will be very entertaining for talks and presentations, and give you an appreciation for the quality of the data that will be used to analyse nesting behavior and diet.
But thats not all. I have been waiting for baited breath to get a new camera. Thrilled to have purchased the Canon SX20 when it first came to the market in 2006, the 20x zoom was the leading point and shoot camera I could find.
This camera tolerated my abuse, and being a permanent fixture on my travels and fieldwork, it gets subjected to all extremes of weather, and some hard knocks. It was still working perfectly when the SX35 came out, and so it was difficult, but somehow I managed to resist upgrading back then. Ever since I have been holding my breath for the next big thing.
Canon Powershot SX50. Thats 50x zoom lens equivalent to 24-1200 35mm. And with digital zoom it can pull 100x zoom! Phwoar! As soon as it hit the shelves I had one in my sweaty hands. Delightful...
The camera sat in my bag for a few days, waiting to christen it with something relevent and important. That chance came with the autopsy of our shot eagle. I was particularly happy with the xray photos. The next chance was a little time-out in my park - and managed to get a few nice pics here.
To complete the trilogy of tech enhancements, the purchase of a new phone was necessary. Months ago I was given a old hand-me-down Nokia. Welcome to the 21st century kiwi, a phone with internet access! With a camera! I quickly found these features enhanced my work efficiency. Answering emails in the field, and taking photos of chicks while at the nest.
The old Nokia cant swim, I found that out recently. Pity... A replacement was needed. So I hope the Nokia C7 will be as durable, welcome to the family, and the school of hard knocks!
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