Category Archives: verreaux’s eagle

Beneficial Birds of Prey and their Effect on Prey

When I first started working in raptor conservation for the Peregrine Fund in early 1990s, my then boss Dr. Rick Watson and I discussed the various merits of raptors. How would we best promote them? They are persecuted widely in Kenya and are not viewed as beneficial. There is very little in the way of appreciation of raptors that actually helps their protection in rural Kenya despite their images being displayed on the back of passenger minibuses (Matatus), on banks, or in the media. There is some to be sure, but I have a feeling that there is less than there was. What raptors there are in human habitats are there mostly because they have evaded persecution. Some have prospered in these altered landscapes, but most have declined or become locally extinct.

Raptors do play a role in curbing plagues of rodents, small seed eating birds, hyrax, monkeys, pigeons and such like. By explaining to an audience the amount eaten (possibly amounting to thousands of tons per year in farming lands of Kenya) it is easy to show a beneficial aspect. Take the raptors away and these prey species will continue to live, multiply and consume more human food. There is the famous example from some unclear study area in South Africa, where the sheep farmers shot out the Verreaux’s Eagle, who undoubtedly took a few live lambs. Within a few years the hyrax swarmed off the Kopjes and out into the sheep pastures, and despite the heavy gun fire wrought by the sheep farmers, they accepted that they lost much of the total sheep productivity than when they had the eagles. Tolerant farmers had eagles, a few wary hyrax, and lots of sheep.

I never really understood that. Predators have been proved in many studies to have minimal effect on the numerical density of their prey species. Disease and starvation are the leading causes of mortality in all species. A few predators thrown into the mix makes not one whit of deference to healthy populations. There is no way a swarming mass of millions of Red Billed Quelea, or a heaving mountainside of plague rodents in the highlands of Ethiopia are going to be affected in the least by birds of prey. Not if you count the amounts eaten per individual raptor and total it up. Impressive as it may be, raptors do not exert that sort of pressure. This argument has been used against those wishing to persecute raptors on Game Bird shooting areas. Grouse are killed by Peregrines, Harriers and Golden Eagles. It is their natural prey. Some game keepers still persist in persecuting raptors so as to increase the amount of grouse. In reality there is no difference between those areas with hawks and those without. The main issue for grouse numbers is food and shelter.

One thing I noticed when on a wheat farm was that a single roving falcon or harrier sets up huge spirals of panicked birds ahead of it. As the hawk moved around conserving energy and looking for easy pickings, the prey burned up so much energy and were highly stressed.

harrierdoves.JPG
Drawing of Harrier scaring doves on farmland

The hawk was a “scare crow,” and it kept the birds from eating. Ultimately must mean less small birds. I should imagine the fat and unfearing hyraxes of South African sheep farms waddling kilometers from cover were sent into a panic when they finally did spot a Verreaux’s Eagle. One Verreaux’s Eagle would not eat that many hyrax, but it sure as heck would change their habits.

In a landscape without raptors prey species may not fear stepping out unprotected into the open. It is this fear, more than the actual mortality of prey that I am sure plays and enormous evolutionary role. It is an understudied aspect of predation.