Environmental Health Implications of the Southern Bypass Road Construction through Ngong Forest on the African Crowned Eagle, Nairobi County


According to Norman Meyers in a study for Friends of Earth, 142,000 Km2 were cleared in 1989 and a further 200,000 Km2 severely degraded. He noted that forest loss has increased since 1979 by 90%, Brazil, Indonesia and Zaire (DRC) which had the highest percentage of natural tropical forests, accounted for half of that (FAO 2003). Regionally, deforestation has also been on the rise. In the Central Africa region, rates of forest loss have surged ahead of this dismaying global average increase (WRI 1992: 285). Africa is losing more than 4 million hectares (9.9 million acres) of forest every year, twice the world’s average deforestation rate according to a statement by the United Nations Environment Programme (UNEP). Four million hectares is roughly the size of Switzerland or slightly bigger than the U.S. state of Maryland. Of worth to note is that natural forests in East Africa total 134 million hectares.

Forests are principally degraded or cleared for agriculture, fuel wood while the main cause of degradation is uncontrolled logging which can be attributed to rising levels of urbanization globally.  Any land-use change within a forest can potentially result in fragmentation. Habitat fragmentation is usually defined as a landscape-scale process involving both habitat loss and the breaking apart of habitat. The extent of the impact will depend on the type of change, the degree of fragmentation, and the species involved. In the early days of settlement, much of the forested landscape was fragmented by land clearing for timber and agriculture. In the more recent decades, some of the most serious fragmentation has been caused by urban sprawl. Urban sprawl refers to new development that consumes land at a rate faster than that at which the population is growing. It uses more land per person combined with the fact that the population itself is steadily increasing in cities and towns. It promotes dependency on the use of cars, because it is characterized by low-density development that separates where people live from where they shop, work and recreate. It also separates them from access to green space and natural areas in their communities because typically natural areas are not incorporated into the design of these developments.

Roads and rights-of-way are a major contributor to habitat fragmentation because they divide large landscapes into smaller patches and convert interior habitat into edge habitat. As additional road construction and timber harvest activities increase habitat fragmentation across large areas, the populations of some species may become isolated, increasing the risk of local extirpations or extinctions (Noss and Cooperrider, 1994).  Some of the primary adverse impacts of roads and highways on wildlife and wildlife habitats include: Direct loss of habitat; Reduction of effective useable habitat near roads for small mammals such as Duikers, Deers and Dik Diks; Direct mortality as a result of game animal/ vehicle collisions; and increased noise and visual disturbance for small mammals such as duikers and Bush Bucks.

The construction of the Ngong Road-bypass intersection through Ngong Forest, now underway, has seen the Kenya Forest Service sacrifice more forest land to create space for this new development. Sadly, the four slip roads that form a clover leaf intersection will see the forest lose thousands of trees. What was once one continuous ecosystem was split into five separate forest sections to give way for the development of the bypass (Ngong Forest Sanctuary). Forest fragmentation can have negative and often irreversible effects on local environments, especially when associated with human development. These negative impacts include reduction of total habitable area; Edge habitation: When a habitat is fragmented, the amount of edge-habitat increases at the expense of interior habitat. Species dependent on interior habitat suffer, while edge-dependent species, including invasive species and predators, thrive. Woodland-dependent bird species, even though they are found in nearby woodland areas, often avoid small fragments; Vulnerability during movement among patches; Isolation of a population; Vulnerability to external competition and predation; Inhibits with flow of genetic materials throughout the landscape as it interferes with breeding and more importantly, interbreeding.

Ngong Forest is the only indigenous forest that is located within Nairobi county, it is rich in biodiversity as it is home to over 175 bird species, over 35 mammals and numerous insects, reptiles, amphibians and fish. One of the important bird species that inhabits the forest, which serves as an indicator of ecosystem health, is the African Crested Eagle. The African Crowned Eagle Stephanoaetus coronatus is Africa’s most powerful raptor. Although not the largest bird of prey, it is considered one of the “Big Three” eagle species in Africa along with the mighty Martial Eagle and the beautiful black Verreaux’s Eagle. (Bill De Guilio). The Crowned Eagle is found only on the continent of Africa. In East Africa, the Crowned Eagle’s range extends from central Ethiopia, to Uganda, forested parts of Kenya and Tanzania to as far south as eastern South Africa, with a southern distribution limit around Knysna. In western and central Africa, the Crowned Eagle’s range extends through much of the (once) vast African rainforest. They may be found from Senegal, The Gambia, Sierra Leone and Cameroon, where they inhabit the Guinean forests, to the Democratic Republic of the Congo, where they live in the Congolian forests, and down south to as far Angola. Despite its large distribution there, the Crowned Eagle is now rare in many parts of West Africa.

Current estimates place the number of African Crowned Eagles at about 10,000 individuals. In 2012 they were listed as Near Threatened by the IUCN (International Union for Conservation of Nature). With widespread deforestation occurring across Africa the amount of suitable habitat for the Crowned Eagle is shrinking and placing a strain on the species. However in South Africa, organizations such as African Raptors and Birdlife international have listed the bird as threatened. The Crowned Eagle inhabits mainly dense woodlands, including those deep within rainforest, but will sometimes also be found in relict patches, wooded escarpments, riparian strips of Acacia, heavily wooded hillsides, and rocky outcrops throughout its range (Kemp, A. C. 1994). Typical of most raptors that breed in Africa, the Crowned Eagle is non-migratory and is largely sedentary. This species usually inhabits a fixed territory throughout the year its adult life. There is evidence that the birds move about to some degree when circumstances require (Oatley, Oschadleus, Navarro and Underhill, 1998). Their diet consists primarily of mammals, especially monkeys, hyraxes and small antelopes, as well as some birds and large monitor lizards. Mates may hunt cooperatively, and share their prey.

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The Crowned Eagle is fairly common in suitable habitat, though at the population level, its numbers have shown a decline in sync with deforestation. Declines appear to be widespread and may be increasing due to the often fevered pace of clear-cutting. This species main habitat is rich, high-canopy forest, which is a major target of timber companies, agriculturists, palm oil and bio-fuel plantations and miners as well as slash and burn farmers. Biologists in Africa now suspect that the Crowned Eagles adaptability to small, fragmented tracts of woodland has been exaggerated in the past. (Thomsett, 2010)

Ngong forest, one of the few indigenous urban forests found within the Nairobi County provides valuable environment services and ecosystem services and also serves as a carbon sink for Nairobi County. The clearance of hectares of forest cover to pave way for the construction of Southern Bypass road has resulted in habitat fragmentation. The forest has been divided into five sections and this had an impact on biodiversity in the forest. The forest serves as a home to one of the few raptors species in the forest, the nearly threatened African Crowned Eagle. The eagle is a non-migratory bird that is accustomed to inhabiting areas with minimal disturbance.

Population dynamics of the African Crowned Eagle

The conservation of raptors is a high priority for many conservation organizations around the world. This is mainly due to the fact that birds, particularly diurnal raptors, are sensitive to ecological changes and habitat disturbance (Thiollay 1985). Brown (1976) has stated that „all threats to eagles are due to humans‟, as they have few natural enemies. Dowsett (1985) supported this by commenting that the major threats to tropical forest birds are “human-induced”.

MacLean (1993) found that the distribution of African Crowned Eagles is now discontinuous due to the fragmented nature of their habitat. He also reported that 65% of original habitat in sub-Saharan Africa has been lost with the rate of deforestation in tropical areas continuing to increase. It is therefore important to conduct a habitat analysis of the African Crowned Eagle in order to understand the habitat requirements of this species. Furthermore, by studying breeding success, we can gain a better knowledge of what threats there are to these birds and how humans can assist the long-term survival of this species. By investigating the roles of exotic plantations, the future of these birds in Southern Africa can be assessed as commercial forestry of exotic plantations is a large-scale industry. Supporting this, Barnes (2000) suggested that the planting of exotic plantations in place of indigenous forests in South Africa is leading to a decline in the African Crowned Eagle.

The conservation of forest raptor species has come under increasing scrutiny due to the large-scale effects of deforestation and habitat fragmentation. The Solitary Crowned Eagle (Harpyhaliaetus coronatus) is an endangered forest eagle in South America, fairly closely related to the African Crowned Eagle. Its current IUCN status is “Endangered” and the severity of its threats “strongly suggest a significant and continuing decline in numbers” (BirdLife International, 2008). BirdLife International (2008) suggests that the main threats to the Crowned Solitary Eagle are habitat destruction and hunting whereas Bellocq et al. (2002) observed that naturally low population numbers combined with habitat fragmentation are the main threats.

Rain forests in Africa are becoming more fragmented, with reports suggesting that only the protection of large areas of forest will conserve many species of African Birds (Beier et al. 2002). Such environmental stresses have meant that mortality factors have become more important in species conservation. One factor is raptor mortality from power line electrocution, where such losses should be compensated by healthy populations (Bevanger, 1998). It has been noted that birds with large and broad wings, as for instance forest eagles, can be susceptible to both electrocution and collisions (Bevanger, 1998). However, there are many other threats to African raptors; transformation of habitat into agriculture and invasive alien vegetation which have been cited as two main factors that have reduced the Black Harrier (Circus maurus) to only 50% of its core breeding habitat in South Africa (Curtis et al., 2004).

Supporting this, Steyn (1982) has reported that in Southern Africa, birds of prey are most threatened due to the “technological advancement of the region”, which is heavily linked to habitat destruction. Steyn (1982) agreed with Brown (1970) who discussed people’s negative attitude towards large eagles, as South African farmers tend to blame large eagles such as the Martial Eagle (Polemaetus bellicosus) for domestic stock losses. However, both Brown (1970) and Steyn (1982) agreed that the eagle is often not to blame for such losses and that this could be an example of prejudice. In support of this Machange et al. (2005) found that eagles were found in significantly higher densities in areas supporting indigenous game than in areas supporting domestic stock.

Disturbance of breeding ground of the African Crowned Eagle

The nests of the African Crowned Eagle can be enormous and are often situated in tall trees, near rivers and streams in the first fork of the tree (Brown et al. 1982, Malan and Shultz, 2002). Despite this, African Crowned Eagle nests are among the most difficult to find of all eagle nests, as they are usually in thick forest (Brown 1966). The eagles prefer the tree to be clear of low-level branches as these often assist nest predators in reaching the nest (Malan and Shultz 2002). Therefore, most nesting sites are found in emergent trees with the main fork above the surrounding canopy for easy access and protection from non-flying nest predators (Shultz and Thomsett 2007). The nests are near the centre of their ranges and so they are termed „central placed foragers‟ (CPF) (Orians and Pearson, 1978). In addition Shultz and Noë (2002) found that the majority of African Crowned Eagle foraging takes place within the centre of their home ranges, this was identified through the use of radio tracking. Nests are re-used as long as there is a pair present in the area and the nest is not excessively disturbed, as findings from Brown et al. (1982) and Steyn (1982) suggest that nests can be older than fifty years.

Breeding success can potentially be influenced by many natural factors, such as prey availability, habitat availability and quality, and climate, and additionally by many anthropogenic factors, such as afforestation which potentially enhances success (Allan et al 1997). Exotic timber plantations are very common in Mpumalanga, South Africa and their effects on nesting bird species has been studied (Allan et al 1997, Malan and Robinson 2001). The use of exotic tree species in forestry plantations, may enhance breeding success of birds by providing suitable trees for nesting (Malan and Robinson 2001) but may reduce success via a reduction in biodiversity in large timber monocultures (Johns 1993). Habitat selection may be linked to breeding success due to the type of prey found in certain habitats. For example Brown (1982) stated that monkeys were only a minor dietary component outside of forests. Boshoff et al. (1994) carried out a dietary comparison across two biomes within South Africa, and reported that although hyraxes (Procaviidae) and antelope (Bovidae) were among the dominant prey types in both, hyraxes were more common prey in savannahs whereas antelope were the most common prey in forests.

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Dietary characteristics of the African Crowned Eagle

There have been many studies of the diet of African Crowned Eagles (Brown 1976, Daneel 1979, Jarvis et al. 1980, Tarboton and Allan 1984, Skorupa 1989, Struhsaker and Leakey 1990, Boshoff 1994, Shultz 2002, Shultz and Thomsett 2007) but a common dietary composition or preference has not been identified. Some studies found a predominance of primates (mainly the family Cercopithecidae) in the diet (Skorupa 1989), others a predominance of small antelopes (Bovidae) (Brown 1972), or rock hyraxes (Procaviidae) (Jarvis et al. 1980). In addition, Boshoff et al. (1994) reported that both rock hyraxes and antelope formed a large component of Crowned Eagle diet. McGraw et al. (2006) found a preference for small Duikers and carnivores despite the majority of prey being primates. Skorupa (1989) commented that by the early 20th century, naturalists were classifying the African Crowned Eagle as a “monkey specialist”, but Brown (1982) had previously stated that monkeys were a minor dietary component outside of rainforests. In the Taï National Park (Ivory Coast), the African Crowned Eagle has been identified as the most prevalent and important predator of mammals (Shultz 2002). Although mammals constitute the majority of their prey, African Crowned Eagles also feed on birds and reptiles, albeit as a much smaller proportion of their diet (Jarvis et al. 1980, Struhsaker and Leakey 1990, Boshoff et al. 1994, Shultz 2002). Studies on predation rates by the African Crowned Eagle (Brown 1976, Shultz 2002) estimate it removed 4 – 9% prey biomass per year. Observations by Brown (1976) included a female African Crowned Eagle consuming 1.1kg of Sunni antelope (Neotragus moschatus) in one meal. However, regardless of the geographical location, these three prey types (antelope, primates and hyraxes) comprise the vast majority of the diet of the African Crowned Eagle. Brown (1966) found that an African Crowned Eagle pair in Kenya were “exclusively mammal-eaters”, but acknowledged that other African Crowned Eagles in other areas did prey on birds and reptiles. In addition African Crowned Eagles have been known to prey on domestic animals, rodents and small carnivores such as mongoose.


In order to ensure the sustainable existence of the African Crowned Eagle in the forest, efforts towards trying to conserve and protect the bird must be undertaken. If not undertaken to protect the natural environment of the bird, its existence in the forest may be jeopardized. To prevent such negative impacts resulting in the future, large infrastructural developments should be avoided in natural areas such as forests such as Ngong forest that serve as a home to a variety of numerous animal species and one of Africa’s most powerful birds of prey, the African Eagle. If it is necessary to undertake infrastructural developments in areas such as forests, Environmental Impact Assessments should be carried out critically so as to ensure that no species of animals of plant will be adversely affected. Long term impacts of such projects should be assessed critically so as to avoid disrupting ecosystems, reduction or loss of biodiversity among other negative environmental impacts.

The population of the African Crowned Eagles in the country needs to be determined so as to determine its status on a national level. This will be in line with the new Wildlife Conservation Act 2013, section 4. This will help in enforcing conversation and management of the species, the review of the national list of wildlife ecosystems and habitats that are threatened or endangered and threatened are in need of protection every five years will also help to monitor the status of the bird regularly as well as other flora and fauna that may become endangered, threatened or in need of protection.


  • Restrict development of construction projects such as the Southern bypass road on natural conservation areas such as forests
  • Environmental Impact Assessment conducted prior to undertaking large construction projects in natural areas should take into all biodiversity within a conservation area and the severity of its potential impacts.
  • Fencing on the individual five section of the forest should be undertaken so as to limit incidences of animals such as Duikers, Bush-back and Antelopes being run over and being injured or being killed as they attempt to cross the 60m width road reserve between forest sections.
  • Collaboration with environmental planners should be considered to facilitate development of 10m buffer zone in areas not covered by the forest to limit noise pollution affecting the animals in the forest.
  • Increase forest patrols by rangers and forest guards to reduce the incidences of felling of indigenous tree species such as the Silver Oak that have significantly reduced in the number of tree stands in the forest.
  • Together with legal bodies such as the Law Society of Kenya, the forest department and sanctuary trust should impose heavy penalties on those found trees in the forest specially indigenous tree species.
  • Close monitoring of the African Crowned Eagle should be undertaking to ensure that any changes in the birds‟ immediate environment are noted to avoid irreversible impacts that could result loss of this species in the forest.
  • Create public awareness of the status of the African Crowned Eagle to enhance conservation measures undertaken.
  • National Museums of Kenya should conduct a regular inventory of the bird so as to monitor the birds status as well as have an up to date database.
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