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Ayres's Hawk-Eagle in the city
For the last few years, observant birders have laid eyes on the magnificent, but little known of, Ayres's Hawk-Eagle a.k.a Ayres' Eagle Hieraaetus ayresii in Gauteng.
I decided in 2014 to make it my ultimate goal to first of all locate a bird in my home city of Pretoria and then go a step further and attempt to establish how many individuals there possibly are which we perhaps overlook on a daily basis seeing
that since their plumages are so variable, that it allows a patient bird with the additional, yet, most possible challenge to id individual birds. Whilst individuals range from very dark birds to very pale birds, the most common is the intermediate morph.
Thus the darker or paler the bird, the better the "find". A very rare black morph, the Holy Grail for any Ayres's enthusiast, exists.
Dark morph Niel Cillie
Pale Morph Niel Cillie
For a long time my searches were futile, until 27 November 2014, coincidentally on my late mom's birthday. After staking out a fairly large area around the Union buildings for 3 successive days, lady luck smiled on me when an
adult bird soared high up above the Union buildings on a very overcast afternoon. I was elated to say the least!
(Hover over the pictures to enlarged) Dirk Human
With the ice now broken, my second sighting of this magnificent species soon followed in Early January 2015. And boy was I treated to a special sighting of a large female Eagle. Females can weigh up to 1.1kg. I watched as this individual made a number of stoops
at some Rock Doves weighing between 320g and 450g and eventually after about 5 attempts, which is an excellent strike rate as the average attempts are around 15, nailed a Rock Dove in mid-air with a sound best described as a parachute opening! It landed in a nearby
tree with its prey where it continued to pluck the dove clean before eating it. Often only a bare skeleton and one leg of the unfortunate dove serve as leftovers.
Intermediate morph Dirk Human
What is noticeable is that the much smaller male Eagle weighing as little as 620g could potentially catch a dove weighing as much as 72.6% of its own weight and carry it off in flight!!
It is by no means easy to separate male from female birds, but with some imagination judging it on top of its prey size wise one could possibly determine the sex. The dove will be between 71 and 76% of the male eagle's size
and between 55 to 59% of the female eagle's size.
Another interesting observation is that during the initial years when Ayres's Hawk-Eagles were first seen in Pretoria, it was between January and April and mainly sightings of immature birds.
All of a sudden for the past 3 years or so more and more adult birds were reported from as early as the 1st of September, as what has been the case with a pale adult this year, reported by Niel Cillie. I was lucky enough to first photograph this
individual on the 11th of November. I decided to name it "Spring day".
This particular one would become an interesting record later on in this article as it would become a much studied bird.
But back to the questions: So why all of a sudden the influx of adult birds?
Have they just been overlooked as they are high soaring birds and spend a great amount of time in densely leaved trees? Or is there something more to it?
Another question that arise is why are these birds present earlier? Could drought higher up in Africa be the reason that these intra-african migrants arrived earlier in South Africa?
An finally how well did they breed this year? Are adult birds here earlier because they did not breed? Well we will only know when the youngsters start arriving in January 2016.
Each breeding pair lay one egg each season between April to May but sometimes even up till September.
Incubation is 43 to 45 days by the female.
Nesting another 73 to 75 days. Again the female feeds the chick with food provided by the male.
The chick is dependent on its parents for +- 3 months after fledging. A total of about 7 months. So that explains why immature birds arrive here in Gauteng late December, early January.
It probably also explains why immature birds are so aggressive towards the adults once they arrive here. Probably attempting to resume dependence on the adults.
Then in October this year a valuable discovery was made when 2 birders observed 2 individual eagles on the top of a hill in Pretoria West in John Keevy drive near Weskoppies hospital. More birders soon headed out to the location
and with regular interval Ayres's Hawk-Eagle sightings were reported from this location. I first visited this site on the 14th of November and soon after arriving a rather dark adult put in an appearance at around 7:30. I named it
"Dark Blotches" after its obvious dark blotch appearance in flight as shown in the picture below.
I was back at the Weskoppies site on the 15th and was greeted by another dark bird as we arrived at 6:40. It did not show the dark blotches of the previous day's bird and neither did it show the worn plumage of "Dark Blotches"
It soon became a regular at this site and its aggresive nature and feeding habit earned it the name of "Monster".
About 30 min later a second much more paler bird with an interesting plumage showed up. My daughter reckoned that its plumage reminded her of a Mcdonalds Oreo icecream - Thus it was dubbed "Oreo". The peak time to view these eagles at the top of John Keevy drive seem to be between 6:30 and 9:00
when they are best viewed from the area between the pine trees and the fence to the right of the radio station, overlooking the parts of Pretoria towards the north and north-west.
So I started recording how many different birds visited the Weskoppies site. My tally after 1 weekend stood at 3 individuals.
Weekend 2 was more frustrating. On 21 November, 2 birds arrived again between 7 and 8 a.m. but never ventured close to the lookout point for
better views. Eventually we decided to head down to where we thought these birds were hunting - silos hosting a significant number of Rock Doves, the primary food source of Ayres's Hawk-Eagles.
On our way there we picked up an intermediate bird in flight, a 2yr old youngster moulting into adult plumage - "Teenager". It soon vanished. Great care must be taken when recording Ayres's as a pale form
Booted Eagle was also recorded on the day, also showing the very distinct "landing lights".
On the 22nd of November we had to work even harder and decided to take up position right at the silos. After about 30 min a pale adult swooped past. I compared my photos of this pale bird with the photos of "Spring day" I photographed
on the 11th and realised that it was the exact same bird! So we now had evidence that they were getting around further than at first thought.
Ayres's Hawk-Eagle hunts in a spectacular fashion by soaring very high, sometimes unseen with the naked eye and usually using a dark overhead cloud or the sun as camouflage. It then drops down after targeting its prey and stoops with wings closed
in a heart-shaped form showing the massive alulas which experts believe are used to aid with direction when in a stoop. The hunt all happens in the blink of an eye as the bird travels at an amazing speed!
"Monster" stooping Dirk Human
Main prey item - Rock Dove Columba livia Dirk Human
There are 2 more individuals which have been seen and photographed by fellow birders at Weskoppies. Another very dark individual as well as a much more paler bird. The 6th and 7th different individuals for the site, which makes it undoubtedly the best and most reliable spot to view this species.
I have not laid eyes on these birds yet, but the streaked throat seems to be a very distinguishing feature for the dark bird and the paler bird has feinter streaking and shows buffy underparts.
"Streaky Throat" Robert Wienand
"Lightly Streaked" Mark Tittley
These eagles seem to favour hills lined with Blue Gum and Pine trees and of course plenty of Rock Doves in close attendance. So any suitable habitat should be explored and monitored for sightings.
There are even reports from a few locations further south in Midrand and Johannesburg.
"Spring day", "Monster" and "Teenager" have become regular performers since we figured out where to look for them. And they treated us to spectacular views whilst hunting and feeding on Rock Doves over the last couple of weeks.
"Spring day" Dirk Human
"Monster" Dirk Human
"Teenager" Dirk Human
As mentioned earlier, the habits and movements of these birds are poorly understood. There is planning underway to trap and fit 2 or 3 birds with satellite tracking devices to conduct further studies.
They have extremely large ranges and their current IUCN Red List category is least concerned, with a population between 670 and 6700 mature birds. Funding is crucial to make this study a success as tracking devices cost R25,000 a unit.
Therefore donations from the public and from companies will play an integral part in learning more about these amazing birds and their movements.