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Competition over an artificial nest by eagles and hawks and what it means for raptor conservation

After watching some 13 failed nesting attempts in 8 years of a pair of Augur Buzzards on Long Hill due to baboon predation I got fed up and chose a new tree, made a new nest and covered the trunk below with barbed wire on the 20th of September 2020. The very next day after completion the buzzards moved in (see vlog Building a Baboon proof nest).

For eight years I have seen the baboons repeatedly tear apart the nests of this pair and of another pair near the north side of lake Elementeita. I have seen them pull down a Martial Eagle nest twice and kill a chick once, tear apart a Brown Snake Eagle nest and constantly stop a pair of Lanner falcons nest on Half Hill, the only suitable cliff on Soysambu Conservancy. It’s rare to catch them in the act, but often the Augur Buzzards scream so loudly in trying to defend their nests I can run out to see it happen. The Lanners noisily attack too and when overwhelmed by up to over 400 baboons they desert the cliff entirely. In the Martial Eagle and the Brown Snake Eagle nests I found baboons, all male, in the trees pulling the nesting material apart. This all occurred near my house, though we know baboon predation to be a serious factor in the near total elimination of nesting Verreaux’s eagle, Egyptian vulture and Lanner falcon in Nakuru park and the main cause of failure of Peregrine falcons nesting at Tsavo East HQ since the early 1970s. Taken at a national level it’s a growing risk facing many threatened to critically endangered raptors. Take as an older and over-simplified example between 1985 and 2000 in Tsavo west, on 15 km from Kitani bridge to Finch Hatton’s, about 15 eagle and vulture nests were destroyed by both baboons and Verreaux’s eagle-owls due to intrusions of livestock.

Wait…why the assumed connection between livestock and baboons and subsequent loss of raptors?

It takes a bit of reasoning to understand that synanthropic wildlife (species that profit from and prefer human landscapes) is a large part of the negative anthropogenic factors that lead to wildlife declines. It’s tough to get your head around it because it’s wildlife against wildlife and that’s the circle of life perception of which we are all aware, even if it seems cruel and harsh. We do accept the principle of competition getting out of hand, and the need to intervene, if exotics such as Prosopis (Mathenge) overtake native trees in Baringo, if water hyacinth takes over water lilies, or exotic Carp and (semi-exotic) Nile Perch take over other fish in our lake. Yet when it is suggested that native species can suddenly explode due to human influences and diminish populations of another native species, that acceptance and understanding is much rarer even though there is no scientific rationale to separate the two, especially in isolated conserved areas that do not have anything approaching a natural ecosystem.

When one species is smarter, more adaptable, able to profit from new human foods and experiences a decline in their predators due to humans and livestock, their populations can grow unimpeded. When their populations grow to a point seldom if ever exceeded previously, ecological changes must logically take place to accommodate them and when you are an omnivore capable of killing medium to even large mammal young, you have a genuine “problem”. Other synanthropic animals that can diminish raptor populations are Egyptian Geese, Pied Crows, Vervet Monkeys, Elephants, Verreaux’s Eagle-owls, but we won’t go into that here.

Augur Buzzard chick aged about 40 days old on 25th of February 2021. The laying date was around the 10th of December 2020, less than 3 months after the pair moved into the new artificial nest. The photo on the right shows the coil of barbed wire that was successful in stopping baboon predation. It is high enough off the ground to not contact an eland or buffalo and giraffes do not climb this hillside.

Most people would agree that if baboons destroy all raptor nests for an entire decade something must be unnatural. So we don’t have a problem convincing people of this “upset in nature’s balance”. Similar natural upsets have been seen repeatedly all over the world. Other countries deal with these upsets by controlling numbers, either by translocations to places that have “too little” of the species or to a much cheaper place six feet underground. The latter raises all sorts of political furor in Kenya and is best left alone. So what else can we do? We can’t just sit around and watch endangered species die off because another species has multiplied enormously and is making a very heavy impact upon them.

I started putting up artificial nests as a boy in a garden on the outskirts of Nairobi in the early 1970s. A Hadada Ibis kept having its chicks plummet to the ground near the garage and it seemed a good thing to glue the sticks together. The garden had lion and rhino and Crowned Eagles nesting in a giant Muno tree. Today it’s a housing estate. So what seemed reasonable “conservation action” to do back then, is a thousand times more important today.

In that garden I also helped strap a collapsing nest of an Augur Buzzard to stop it from falling. It worked. Later I took to fixing old nests of Crowned Eagles in Ololua forest, of Ayres’s Hawk-Eagle nests, which are notorious for being badly built, and made a few totally fake nests that got occupied by Harrier Hawks and Black Sparrowhawks. In the Aberdares, as an older teenager, I reinforced one massive Crowned Eagle nest that I also happened to put an unrelated chick into and have it adopted by the resident pair. This was published and was contemporary to similar nest augmentation projects that helped reestablish the Spanish Imperial Eagle and Lesser Spotted Eagle. Those mid 1970s projects got great acclaim, loads of support and led to species recovery. Spurred on by a request by the London Zoological Society to write about it I continued making the odd nest, placing a rehab Mackinder’s Eagle Owl in one nest carved in a cave, who lived there for a year or more. Knocked out a similar cave for Peregrines over the Amboni River (which had Lanners in it some 30 years later), and when I moved to Athi Plains I did the same with a pair of African Hawk-Eagles with whom I was doing Cain and Abel management and needed to double the size of the nest so that both chicks could be in it together. But from this an unplanned but very significant event occurred. White-backed vultures would come and steal the nest, so I’d build another, and another pair of White-backed vultures would come and steal this too. There were White-backed’s nests in the tall acacia already but they certainly profited greatly by the expansion of their colony by virtue of me trying to manage the African Hawk-Eagles. One year a Bateleur took over one of the artificial nests. I built three nests for a pair of Martial Eagles too, because the quality of the trees couldn’t properly support big nests. I wasn’t much interested in the “least concern” vultures then, but decades later we can confidently say that if you want to augment the now “critically endangered” White-backed Vulture, we have a proven technique. One that is hands off and non-invasive.

While Carter Ong Smith was doing her MPhil in the mid 1990s on the biology of the Martial Eagle, I would on occasion add some reinforcement to the nests we found. It was good to know that when Shiv Kapila and Sydney Shema went back 25 years later some of these nests were still used. More interestingly, even if the tree had since fallen, the birds remained “glued” to the site that was set up for them.

Martial Eagle of the Volcano pair on the 11th of September 2022, a few days after their first attempted occupancy of the artificial Augur Buzzard nest on Long Hill. The Augur Buzzard pair were very upset and risked their lives time after time hitting the eagles and the eagles responded by flipping on their backs to “foot” them in mid air.

In looking back I have made or reconstructed/reinforced nests for : Martial Eagle, Crowned Eagle, Verreaux’s Eagle, African Hawk-Eagle, Tawny Eagle, Ayres’s Hawk-Eagle, Cassin’s Hawk-Eagle, Bateleur, Brown and Black-chested Snake-Eagle, Augur Buzzard, Harrier Hawk, Black Sparrowhawk, African Goshawk, Little Sparrowhawk, Gabar Goshawk, Lanner and Peregrine Falcon, Yellow billed Kite, White-backed Vulture, Lammergeyer and in Nepal with colleagues Tulsi Subedi and Sandesh Gurung we deliberately tried to initiate an augmentation project for the Indian Spotted Eagle. In Madagascar I put up a number of artificial nests for their Endangered Fish Eagle, again because we needed extra space for the rearing of Cain and Abel.

In this I haven’t added the owl nest boxes, the norm in the backyard of many millions of houses across Europe and the USA. We’ve done our bit here, especially Shiv Kapila at Naivasha who has handed out ready made boxes to so many. These get mostly barn owls and Spotted Eagle Owls and a few Pearl Spotted Owlets.

When one pauses to add the number of years they have been up, the number of “extra success” of these 25 odd species of diurnal raptors over as many as 4 decades one is looking at some 600 extra birds minimum if they just had one chick per year. That’s an entire national park’s population plus some. So it's not insignificant. It may be if you don your scientific hat and factor in natural mortality rates because the sad fact is everything living dies. But let’s remove those grumpy, clean finger-nailed scientific geeks who have never climbed a tree and consider the facts. Actions like this have turned around the destiny of a number of raptor species globally. There are very few options open to us, and this is one that is globally commonplace and locally acceptable.

To return to those Augur Buzzards who raised their first young in the artificial nest on Long Hill and successfully had their chick after nearly a year of parental care move on, 2022 was a bad year for them. The drought of mid 2022 did them no favour, but they had their young killed by a juvenile male Martial Eagle from the volcano pair. And now, as I write, the volcano Martial Eagle pair has moved in to take procession of this nest. For the record I have reinforced a nest for the Volcano pair, rebuilt it after a fire, reinforced another and then see they have moved into this Augur nest.

What does this tell us? 1. There are very few available nesting trees, and 2. There are few nesting trees that are non accessible to baboons. So much so that the Augurs and the Martials are fighting over one tree right now…

Can we do something to help?

You betcha!


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Kenya Bird of Prey Trust

Understand - Protect - Restore

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