African Fish Eagle Behavioural Studies
We have been monitoring a young African Fish Eagle (Haliaeetus vocifer) pair since they were first observed in October 2004 in the Kromdraai Conservancy within the Cradle of Humankind World Heritage Site.
The female being older was estimated to be 4 years old whilst the male was yet sub-adult and approximately 2 years old. For sixteen months, the pair frequented two sites simultaneously approximately 4 km apart. When Lake Heritage became established – a large manmade dam constructed by the late Franz Richter on the farms of Aloe Ridge Hotel and Heia Safari Ranch in the Muldersdrift district, Gauteng Province – did they permanently relocate during January 2006 where they’ve made this site their home.
Their first ever breeding attempt was in June/July 2007, which ended catastrophically in that the substructure of their estimated 18m high eucalypt tree nest collapsed under its own weight whilst being buffeted by a four-day windy spell only two weeks into incubation.
Deemed to be at the right place at the right time, sticks and nesting debris lay strewn on the ground and in our presence both eggs dislodged from the nest cup remains hurtling to the ground and disintegrating on impact. Having studied the shattered eggs it was of particular interest to note that neither contained embryos and although traces of blood were evident, the bulk consisted only of albumen. It is highly probable thus that when the eagles abandoned their incubation, crows scavenged the eggs and consumed the contents thereof. As Pied Crows are in relative abundance at least 12-18 have on regular occasions been observed flying high along the cliffs of the nearby Zwartkop Hill.
As both eagles were novices at the fine art of nest construction and as it was their first attempt, we had no desire to possibly stand witness to a reoccurring scenario where a new nest might be constructed within the same high canopy of eucalypts where the previous nest failed. An alternative plan had to be made to assist the eagles with a new manmade nest and from donations procured from Steel & Pipe for Africa (Pretoria West) and Sun Timber Sales CC specifically intended for this project, we were ready to get the project on the road.
Chris van Rooyen of the Industries Partnerships Program and André Botha of the Birds of Prey Working Group of the Endangered Wildlife Trust, forwarded us the contact details of Dr. Andrew Jenkins of the Western Cape Raptor Research Program who has had numerous experiences with artificial nesting platforms and he generously provided contact details for Walter Neser, a eucalypt tree climber extraordinaire!
Having met Walter on site on Friday 22 February 2008, he made an assessment of two eucalypts within a copse of about 40 trees and thereafter narrowed it down to one very tall tree that he felt was most suited to build a nest in. Only 1½ days later and on Sunday morning 24 February, Walter came fully equipped with mountaineering gear and special spiked footwear and proceeded climbing the tall eucalypt with expert ease. Passing numerous obstacles on-route, these were tackled individually and 10 minutes later he sat perched in the large and equally sturdy double fork in the main trunk where the nest was to be built 23 m above ground! Settling in, he contemplated his next moves and climbed another 3 m higher to secure his remote controlled video camera to a higher branch yet that would record the nest building activities.
With Teresa Moore, Samantha Meyer and I on the ground, Walter instructed what range of branch material he wanted, inclusive of lengths and diameters. Commencing with 30 to 50 mm thick branches, 10 bundles were tied and hoisted up by Walter who the proceeded in placing each stick individually. Thereafter, 6 bundles of thinner branches that were about 20 to 30 mm thick was collected and hoisted up followed by another 4 bundles of thin 10 to 15 mm thick twigs complete with leaves to form the nest lining. It was pretty hard work searching for, collecting and bundling the branches and we pretty much cleared the entire area of fallen debris. Ultimately 20 bundles had been hoisted up taking 3½ hours to construct the entire nest and readying it for immediate occupation!
As if that was not enough work for the morning, Walter proceeded to climb another 4 m higher onto another lateral forked branch that he felt required felling – crazy indeed! Lying on top of the sloping branch in an awkward position started to saw through two 200 mm thick branches taking another 10 minutes to drop. Content with his achievement, he collected his equipment and abseiled to terra firma in 20 seconds, a job well executed!
After almost ‘drowning’ himself with 1.5 liters of water, Walter told us in his casual by-the-way laidback coolness…that this was his first ever attempt at constructing an entirely new nest from scratch!
All we want to see now is the expressions upon the eagles’ faces when they come home to roost and find a brand-spanking new nest in their midst that wasn’t there this morning…it can only be a great surprise-surprise!
On the recommendation of Walter that four 10 to 15 m high eucalypts be felled to facilitate both adult eagles and future juveniles with an easier flight path to and from the nest towards the water’s edge, the site was thus revisited on Sunday morning 2 March with People for Wildlife rangers to assist with the felling. On our approach and about 80 m from the copse of eucalypts, movement was detected on the nest and fearing that Egyptian geese had already occupied it, fortunately, on closer inspection saw the female eagle perched on the nest’s rim an awesome sight indeed!
The felling of the trees was thus abandoned for fear of disturbing the eagles and as we were later informed by Aloe Ridge rangers that the eagles had already been observed frequenting the nest regularly, which was an added bonus.
Excited that we were able to make a difference for the eagle pair, they too can now breed assured that their nest will withstand the rigors of nature and above all a nest that should endure the test of time. The pair successfully bred on this nest from 2008 to 2015 when we officially stopped observing the pair on a regular basis.
However, during the latter part of the 2009 breeding season the female died when she was electrocuted by a faulty power line on the property and her decomposing remains were found by chance during a territorial walk by project members.
Most fortunately, the surviving male eagle managed to find another female before the 2010 breeding season commenced. At the time when I stopped observing at the end of the 2015 breeding season, management advised me that the pair was still breeding on the same nest right through 2020, which is good news indeed.
Swartland, Clarens, 9707
+27 (79) 505-6419