Underpass for elephants on Mount Kenya [East Africa]

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By Bruce Byers

Bruce is an ecologist, writer, and independent consultant.

We need to move toward a spatial pattern in which human activities are scattered in a sea of natural ecosystems, rather than the reverse—natural ecosystems embedded in a human-dominated landscape, as now in most places. Ecological connectivity between wild ecosystems needs to increase to maintain biodiversity in the face of, and for resilience to, climate change, and human infrastructural connectivity to decrease or be adapted to enable ecological reconnection. A small experiment in northern Kenya is working on the problem there.

I first visited the Lewa Wildlife Conservancy on the north side of Mount Kenya in 2011 while conducting a biodiversity analysis for the U.S. Agency for International Development. We travelled to Lewa on Kenya Highway A2, the main road north from Nairobi to Ethiopia. The road crosses the equator on the outskirts of Nanyuki, and continues around the northern flank of Mount Kenya, the second-tallest mountain in Africa. Its volcanic core is encircled by a roughly circular area of heathland and forests, protected in the 2100 km2 Mount Kenya National Park, which is itself part of the larger 5700 km2 Mount Kenya-Lewa UNESCO Biosphere Reserve.

Northeast of Nanyuki the road crossed what looked like Kansas in Kenya—huge wheat fields stretched as far as the eye could see. At this elevation and in the monsoon rain shadow of the mountain, the climate is ideal for growing wheat, and here the natural forests had all been cleared, and the reddish soil was gullying badly in many areas. 

We discussed Lewa’s conservation initiatives (they are a private nonprofit international wildlife conservancy founded in 1995) with Mike Watson, the conservancy’s chief executive officer. He told us that among the group of radio-collared elephants that were being tracked at Lewa, the records showed one of them repeatedly crossing the road we had just come down and heading for Mount Kenya. They nicknamed this one “Mountain Bull,” and speculated that he was following a traditional elephant movement corridor from the plains around Lewa through a remaining forest patch called the Ngare Ndare Forest and up into the forests surrounding the mountain.

Based on their tracking records, it appeared to be a migratory tradition that was almost lost. On the strength of that evidence and as something of an experiment, a large tunnel, or underpass, was constructed under the A2 Highway between Nanyuki and Isiolo. It was a concrete box four and a half meters high and the same wide under the road at the bottom of a small drainage, which seemed to be a natural place for elephants to move up and down across the landscape. The electrified game fence that surrounds Lewa and the Ngare Ndare Forest was funneled into the tunnel, and more fencing on the uphill side opened toward the sparse cedars reaching through the wheat fields and small farms toward the national park.

Wildlife underpass with truck passing on Kenya Highway A2 (photo by Bruce Byers in 2011)

The underpass seemed to have an immediate positive effect, Mike told us then. A radio-collared bull nicknamed “Tony” was the first to use the tunnel, only four days after it was opened, and about 250 elephants passed through in the first six months.

Mike took us into the elephant tracking room at the Lewa headquarters, and displayed a large Google Earth map with colored lines showing the movement patterns of collared elephants. It showed that the elephants that pass through Lewa move long distances to the north, into the community conservancies in the Samburu-Laikipia area, whose elephant population is thought to be the second largest in Kenya, numbering around 7500 animals. Around 2000 elephants are thought to inhabit the forests surrounding Mount Kenya.

What’s the connection, what’s the story behind the movements of elephants from the Lewa and Samburu plains to the forest belt around the mountain? African elephant populations are increasingly fragmented and isolated. A major cause of that fragmentation was the illegal ivory trade that flourished in East Africa in the 1970s and 1980s. It is estimated that before the international ivory trade ban took effect in 1990, 90% of Kenya’s elephants were killed. Elephant numbers are growing now (at about 5% per year), but so is Kenya’s human population (at around 2.5% per year)

The conversion of wild, open lands for agriculture and human settlements, and transportation and energy infrastructure in wildlife dispersal areas and migration corridors, create more and more opportunity for human-elephant conflicts. Conserving wildlife dispersal and movement corridors that improve the connectivity of the wild landscape is now a high priority in the Lewa Wildlife Conservancy’s conservation strategy.

I was curious about how the elephant underpass has been working in the dozen years since my first visit to Lewa, so I reached out to Mike Watson and Dominic Maringa, the head of conservation and wildlife operations, for an update. An infrared motion-triggered wildlife camera installed in the underpass tunnel has been taking pictures of passing animals since 2013, so there is a lot of information to analyze.

Elephant using the underpass (photo by Lewa Wildlife Conservancy in 2019)

Elephants are the most common users, and their use of the underpass increased rapidly after it was installed; by 2015 more than a thousand elephant transits under the highway were recorded each year, with some of those animals going back and forth a number of times. Spotted hyenas use the tunnel regularly, as do a fair number of buffalo and waterbuck. It is also used occasionally by bushbuck, reedbuck, baboons, and leopards. A total of 17 species have been seen on camera.

Buffalo using the underpass (photo by Lewa Wildlife Conservancy in 2021)

Encouraged by animal transit data from the first underpass, a second underpass was constructed in 2018 under a newly built road through the farming belt south of the A2 Highway, which crosses the stream used by elephants as a corridor to the mountain near the town of Ntirimiti. Cameras are also recording wildlife use there.

On my first visit to Lewa, Mike Watson had described to us how different the elephants in the Mount Kenya forests are than the lowland elephants. Whereas the lowland animals have mostly smooth feet, he described how the feet of a Mount Kenya elephant they darted to install a radio tracking collar were very wrinkled—like deep-treaded tires made for driving in mud, he said.

Do these elephants interbreed? The population genetic structure and regional differences among elephants in Kenya were described by John Okello and coauthors in a 2008 article titled Population Genetic Structure of Savannah Elephants in Kenya: Conservation and Management Implications. Their research revealed three genetically differentiated groups of elephants based on mitochondrial DNA, which is inherited only through mothers. They speculate that these three groups—basically from northern, western, and southern Kenya—may reflect “the genetic signature of mid-Holocene climatic change in Africa and effects of recent poaching pressure.”

Elephant societies are matrilineal and female-led, and females don’t like to wander much, but are quite faithful to the territories they have learned to live in from their mothers and grandmothers. The research showed, however, that most elephants in Kenya contain a mixture of genes from all of the three regional maternal DNA groups, and the epicenter of that diversity and mixing is Mount Kenya. Okello and colleagues propose that “male-mediated gene flow” is responsible for the mixing of mitochondrial DNA types and the lack of significant regional population differences in nuclear genes, which are inherited from both fathers and mothers. A more recent population genetic study (2012) of elephants in northern Tanzania and southwestern Kenya by Marissa Ahlering and her colleagues confirmed the picture of strong female philopatry and gene flow mediated primarily by male movements.

It seems that elephant bulls like to wander, and it is probable that the bulls that move up from the northern plains through Lewa mate with the resident females living in the forests around Mount Kenya, keeping the genes flowing between these elephant ecotypes. That genetic mixing is likely to be needed to enable elephants to adapt to changes in climate that are coming, just as it has been in the past. Keeping conservation areas connected by migratory corridors across landscapes increasingly crowded with people and infrastructure is essential. The wildlife underpasses above Lewa are a small but hopeful success story.

Location of the underpass