Friday, May 31, 2013

Zimbali Coastal Resort

Invitation article by
Geoff Nichols
Environmental Consultant to Zimbali Coastal Resort

Zimbali Coastal Resort, encompasses 456 hectares – originally 70% forest (a combination of natural forest, sugarcane fields, and plantations of Casuarina and Gum trees) and 30% cultivated land – has, with careful planning and eco-sensitive development, been transformed into 85% development and 15% forest.  Owing to the ethos “living in harmony with nature”, Zimbali has matured into a protected natural environment comprising ecological richness and biological diversity.

The developed areas of the estate include private gardens, verges and the golf course – all of which provide refuge to the wide array of birds and animals that would otherwise be unable to inhabit the estate. Although the wetlands have remained intact, Zimbali has lost several “specialist” bird species (mostly due to human disturbance during the early development stages). A number of “generalists” have since taken their place.

Due to the success of the estate’s strict conservation policy, Zimbali Coastal Resort has acted as a conservancy for the re-establishment of many threatened indigenous species, providing a secure home to a variety of local flora and fauna, including over 220 species of bird and no less than 34 species of mammal. Zimbali Coastal Resort has been awarded two environmental accolades: the Nedbank/Mail & Guardian Green Trust Award in the corporate award category (Moreland Developments, 2000); and the more recent award from South African Landscapers Institute(SALI) for the Best Environmental Landscape Work in South Africa (Leitch Landscapes, 2010).

Zimbali Coastal Resort’s habitable environment supports a variety of predatory birds known as raptors. In order for these birds to survive at the top of their food chain and breed, all the other links in this food chain or pyramid must be intact or the raptors will be forced to relocate to a more suitable environment.

There are only about 25 individual birds that prey on other creatures in Zimbali, namely a pair of Crowned Eagles, a pair of African Fish Eagles, two pairs of Yellow-billed Kites that nest on the estate, a pair of Black Sparrowhawk, a pair of African Goshawks, a pair of Little Sparrowhawks, and approximately five pairs of Spotted Eagle Owls.

A single Long-crested Eagle is often seen sitting on posts along the road reserve verges of the M4 provincial road on the west boundary of Zimbali. Among other visitors is an African Harrier Hawk attacking Village Weavers at their nesting colony, as well as Little Swifts colonies under the bridges.

The two raptors most regularly encountered are the African Crowned Eagle and the African Fish Eagle; the former identified by its steep, undulating aerial displays, and the latter by its yelping, echoing call over its open water hunting habitat. Also, the African Goshawk with its high  aerial displays above the forest canopy at dawn and dusk while uttering its chik-chik-chik call every few seconds before folding its wings and plunging back down into the canopy.

Besides covering a large area, Zimbali also features sufficient intact coastal lowland forest to support the requisites of a pair of Africa’s largest forest raptor, the African Crowned Eagle. These majestic birds breed approx. 25m from the ground, within view of visitors to the Fairmont Zimbali Lodge. Their aerial mating display is a steep diving, undulating affair high above the forest which is accompanied by their loud yelping call. To hear this evocative call is a spectacular experience.

The pair of African Crowned Eagles returned to Zimbali to breed during the 2001 and 2002 breeding season, and has since fledged nine chicks. These birds only produce one chick per breeding cycle. They prey primarily on Vervet Monkeys and Blue Duiker that they ambush in open glades or verges in the forest. For them to successfully fledge a young eagle there has to be enough food to feed both the parents and the young fledgling. This pair has become quite habituated to humans watching them.

Zimbali has also the most varied set of prey items of any of the urban adapted eagles studied as part of this work. Shane McPherson has identified that, "The parent eagles delivered 87 prey animals to the young eaglet during approximately five months of camera-monitoring. The primary prey includes Vervet Monkeys, Blue Duiker, and Hadeda Ibis nestlings. Prey of secondary importance includes several cane rats, galago's (bushbabies) and mongooses. Interesting one-off records include a young bushbuck, a crested guineafowl, a dove squab, a golden mole, and an owl as well!”

These eagles have given Zimbali Coastal Resort the best environmental achievement award in that the variety of prey items is a reflection of the varied and rich biodiversity of other birds and mammals that live and breed amongst humans.

Spotted Ground Thrush at Zimbali

Mother-of-pearl at Zimbali

Crowned Eagle at Zimbali

The nest was best visible from the roof of the Fairmont Lodge in 2012

Pruning has opened the view to the nest from the Fairmont Lodge balcony for 2013

Installed camera

Happy family

Sharing a table

Egyptian Goose below the Crowned Eagle nest

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)

Photo by Adele Kieser

Monday, May 27, 2013

The largest eagle to have ever lived

The Haast Eagle, Harpagornis moorei, was the largest eagle to have ever lived.  Sadly very few humans had the chance to appreciate its awe inspiring power and magnificence, as it became extinct within a couple of hundred years of the arrival of the first people to the islands of New Zealand. Those people that may have come into contact with this eagle would have been filled with equal parts of admiration and fear, as the eagle would likely not have given it a second thought on whether to attack and eat these bony stringy new arrivals to its world.

Using skeletal remains and scaling up from existing forest eagles, Haast eagle would have weighed at least 13kg! The largest existing eagle, the Harpy Eagle, typically tops the scales at 9kg, while the Crowned Eagle, impressive as it is, is a lightweight by comparison at nearly 5kg (given weights of the larger female). While the wingspan measurements of 2.5 to 3 meters are similar to long-winged eagles such as wedge-tailed eagle, golden eagle, and stellar sea-eagle, the forest-raptor composition of short wings and massive bulk was unrivaled. The foot mass and structures for powerful tendons indicate great strength, suggesting this eagle had ample capacity to subdue the largest of prey - indeed there are hip bones of Giant Moa with talon holes matching those of the Haast Eagle. Though prey would more typically have been smaller birds; such as the smaller species of moas, flightless geese, rails, and takahe - prey that it could kill instantly (avoiding potential injury) and carry off to devour in peace or carry to the nest site.

The nearest common ancestor to this behemoth is the petite Little Eagle of Australia.  Using genetic markers as measures of time, it is estimated that the Haast Eagle scaled up from a diminutive eagle about 1kg in size to a 15kg monster over just 0.7 - 1.8 million years.  This is one of the most extreme and rapid examples of island gigantism you could find - arising because of a completely unchallenged fitness landscape involving large and flightless bird prey in forested and mountainous environments.

Size of a Wedge-tailed Eagle [C] and male Haast Eagle [D]. from Brathwaite 1992.

Life sized silhouette at Wingspan National Bird of Prey Centre. Photo Claire Raisin

A Haast Eagle being mobbed by Karearea in the southern high country. Tennison & Martinson 2006.

display piece at Te Papa museum

Pre-human ecology of New Zealand was one of the last large untouched landmasses on Earth, a remote south Pacific paradise of birds. The only mammals here were three species of bat, and so all of the bird and reptile species that arrived in Zealandia after the drowning of Tasmantis 23 mya were free to develop quirky characteristics. Most influential of all in this ecosystem of eagle food were the 12 or so species of Moa, ratites that occupied every corner of the main islands; from the smaller Upland Moa weighing 30kg, to the enormous South Island Giant Moa Dinornis robustus, over 200kg and exceeded in size only by the Giant Elephant Bird of Madagascar. This diversity of moa: grazers of the alpine grasslands and browsers of the forest interior, were accompanied by a whole assortment of other large flightless birds now extinct. Even the tiniest birds, a genus of Wrens unique to New Zealand, included some species that were flightless, which would have lived scurrying about the forest canopy searching for all manner of small insects.

Relative size of four species 1-N.I. Giant, 2-Eastern, 3-Little Bush, and 4. S.I. Giant Moa. 

Upland Moa, South Island Goose, and Stout Legged Wren. Tennison & Martinson 2006.
Three diurnal raptors inhabited this lost world, bird predators in a bird paradise. While the Haast Eagle was a giant, another unique and notable predator was the Eyles Harrier.  This was the middle-class predator.  Island gigantism and the ‘forest raptor’ transformation took hold of this Harrier too so that, with short wings, long tail, and strong sturdy legs and feet, Eyles Harrier hunted these forests in much the same way as a large goshawk or hawk-eagle might - far removed from the lifestyle of the swamp harrier that quarters open country farmland these days. The smallest raptor is the only one that managed to persist through the extinction events that followed human arrival.  This is also one of the quirky examples of unique NZ. The Karearea is a short-winged falcon, and a pursuit predator of note. It is much admired as the head-piece of the 20 dollar note, and with a rewarding publicity boost, managed to win the top spot in the 2012 bird of the year.  The existence of these rapacious predators may have pushed some of New Zealands most iconic existing birds, the Kakapo, and Kiwi, to nocturnal lives.

The drama of talons from the skies kept all the birdlife on edge, the isolation and eternal absence of terrestrial teeth-and-fur set the stage for a great fall of this easy living menagerie. The sudden arrival of Polynesian settles – who soon became uniquely Maori - made landfall with an effective toolkit and deftly knowledge.  Moa were most likely completely nonchalant about another bipedal inhabitant to share the islands with, making them simple to walk up to and bop them on the head for a great chicken roast. Stone weapons and fire were used with shocking effectiveness, clearing land, burning forest and cooking all the beasts that roamed.  Some midden sites dating to moa-hunting periods are vast collection containing thousands of moas and many unopened ovens and articulated remains suggest huge wastage in the early days of plenty.  The Maori people arrived sometime around 1200AD, and moa do not appear in middens after 1550AD.

This great eagle would have suffered at the loss of so much of its prey base at the hands of this profligate competitor.  Haast eagle was likely to have failed to discern one bipedal animal from another, and looked upon humans as a scrawny stringy version of its typical moa prey especially if donned with a feather cloak . If the eagle typically hunted 100kg moa, then an adult person much less a child, would have been easy game. A few of the skeletal remains of Haast eagle have been found in Maori middens, so while the loss of its prey due to competition was a major contributor, the Maori appear also to have hunted and eaten them.  Whether this is an act of a pre-emptive strike to protect family and hunting parties, of selfish elimination of a competitor, or prestige and bravery where the mana of the eagle could have been absorbed by consumption.

The Haast Eagle goes by one or other Maori names, Te Pouakai and Te Hokioi.  Two Maori legends legends exemplify its lost magnificence.

Illustration by Colin Edgerley in New Zealand Geographic. 

Te Pouakai

Pouakai was a fabled flying beast which would snatch unwary children who ventured out too early in the mornings or stayed away from their homes late in the evenings. These stories are part of the tribal lore of most Taranaki, Tainui and Whanganui tribes. One such story was told to John White in the late 1880s.
For some years one of the huge creatures had been terrorising the people of an inland village in the hills north-east of Taranaki mountain. Although its wings made a loud noise as it flew, it was so fast that several people had been caught and killed.
A visiting chief, Te Hauotawera, saw how afraid the people were and offered to destroy the beast, provided a group of men would follow his instructions. This was agreed and the party went out one dark night to a large pool near the lair of the taniwha and covered it with a network of manuka saplings and large fern fronds. The men then hid under the network with long sharp spears.
When daylight came Te Hauotawera stepped out of hiding to taunt the man-killer and lure him into an attack. Before long the sound of huge wings could be heard and the brave young chief managed to get under the sapling network just as the huge talons reached for him.
The hidden men thrust their spears upwards and after a long struggle the pouakai lay dead.

       - excerpt Taranaki Daily Times, Fairfax NZ News

Te Hokioi Travels to the Heavens

Te Hokioi, was seen by our ancestors. We (of the present day) have not seen it – that bird has disappeared now-a-days. The statement of our ancestor was that it was a powerful bird, a very powerful bird. It was a very large hawk. Its resting place was on the top of mountains; it did not rest on the plains. On the days in which it was on the wing our ancestors saw it; it was not seen every day as its abiding place was on the mountains. Its colour was red and black and white. It was a bird of (black) feathers, tinged with yellow and green; it had a bunch of red feathers on top of its head. It was a large bird, as large as a Moa. Its rival was the hawk. The hawk said it could reach the heavens; Te Hokioi said it could reach the heavens; there was contention between them. The hokioi said to the hawk, “what shall be your sign?” The hawk replied, “kei”. Then the hawk asked, “what is to be your sign?” The hokioi replied, “hokioi-hokioi-hu-u.” These were their words. They then flew and approached the heavens. The winds and the clouds came. The hawk called out “kei” and descended, it could go no further on account of the winds and the clouds, but the hokioi disappeared into the heavens.

     - from Riley, M. 2001. Maori Bird Lore. Viking Sevenseas NZ Ltd.


Anderson, A. 1989. Prodigious Birds: moa and moa-hunting in prehistoric New Zealand.

Brathwaite, DH. 1992. Notes on the weight, flying ability, habitat, and prey of Haasts Eagle. Notornis 39(4).

Bunce M, Szulkin M, Lerner HRL, Barnes I, Shapiro B, et al. (2005) Ancient DNA Provides New Insights into the Evolutionary History of New Zealand's Extinct Giant Eagle. PLoS Biol 3(1):

Campbell, Hamish; Gerard Hutching (2007). In Search of Ancient New Zealand. North Shore, New Zealand: Penguin Books. pp. 166–167.

Holdaway, R. N. 1991. Systematics and Palaeobiology of Haast’s Eagle Harpagornis moorei Haast 1872. PhD thesis Christchurch: University of Canterbury

Lundmark, C. 2005. Evolutions fast lane. Bioscience 55(2).

Tennison, A., and Martinson, P. 2006. Extinct birds of New Zealand. Te Papa Press, Wellington, New Zealand