Roadless Wilderness Area Determines Forest Elephant Movements in the Congo Basin

Abstract

A dramatic expansion of road building is underway in the Congo Basin fuelled by private enterprise, international aid, and government aspirations. Among the great wilderness areas on earth, the Congo Basin is outstanding for its high biodiversity, particularly mobile megafauna including forest elephants (Loxodonta africana cyclotis). The abundance of many mammal species in the Basin increases with distance from roads due to hunting pressure, but the impacts of road proliferation on the movements of individuals are unknown. We investigated the ranging behaviour of forest elephants in relation to roads and roadless wilderness by fitting GPS telemetry collars onto a sample of 28 forest elephants living in six priority conservation areas. We show that the size of roadless wilderness is a strong determinant of home range size in this species. Though our study sites included the largest wilderness areas in central African forests, none of 4 home range metrics we calculated, including core area, tended toward an asymptote with increasing wilderness size, suggesting that uninhibited ranging in forest elephants no longer exists. Furthermore we show that roads outside protected areas which are not protected from hunting are a formidable barrier to movement while roads inside protected areas are not. Only 1 elephant from our sample crossed an unprotected road. During crossings her mean speed increased 14-fold compared to normal movements. Forest elephants are increasingly confined and constrained by roads across the Congo Basin which is reducing effective habitat availability and isolating populations, significantly threatening long term conservation efforts. If the current road development trajectory continues, forest wildernesses and the forest elephants they contain will collapse.

Impacts of roads and linear clearings on tropical forests

“…Mortality from road kill and predation are generally limited to the road surface or adjoining road verges. Hunting by humans near roads, however, can create zones of elevated mortality and animal avoidance within at least 5-10 km of roads, and possibly much further for wideranging species, such as forest elephants and some primates [44][45][46]. Notably, the traits that predispose species to road kill (Box 1), such as slow movement, poor eyesight and edge-favoring behavior, are often different from those, such as large body size, gregarious social systems, conspicuous calls or displays and the use of regular pathways, that predispose them to hunting or trapping by humans [43,47].…”

“…One of the most striking features of tropical forests is the high proportion of species, including various beetles, flies, ants, bees, butterflies, amphibians, reptiles, birds, bats and small and large mammals, that tend to avoid even narrow (<30-m wide) clearings or forest edges [7][8][9][10][11][12][13][32][33][34][35]40,41,[44][45][46]48,49]. Evidence for avoidance of edges and clearings comes from (ii) predominantly arboreal species that occasionally traverse open ground, such as tree-kangaroos, sloths and many primates [100]; and (iii) slower-flying birds, bats and insects with low flight paths [5, 91,101].…”

“…Avoidance of forest edges and clearings is believed to occur because tropical species: (i) have locomotor specializations, such as being strictly arboreal [50] or adapted for flying in dense, cluttered environments [48]; (ii) require dark, humid microclimates or specialized food resources [7][8][9][10]13,49]; (iii) exhibit strong psychological avoidance of clearings, presumably because of past selection pressures [8,11]; (iv) shun humans or traffic noise, light, movement and air pollution near roads [41,46,51]; (v) are repelled by invasive or generalist species in clearings [32,52,53] (P. Byrnes, Honours thesis, James Cook University 2002); and (vi) align their defended territories with clearing boundaries, thereby suppressing local movements by conspecihcs [11,13]. In general, these traits are opposite to those that promote road kill (Box 1) because the latter results from attempted road-crossing movements [5, 6,13].…”

Regional Action Plan for the Conservation of Western Lowland Gorillas and Central Chimpanzees 2015–2025

“…The vector or reservoir of the virus is strongly suspected to be bats (Pigott et al 2014), but once the disease infects a great ape population, it spreads rapidly, affecting a large proportion of individuals. There is some evidence that physical and 'fear-generated' barriers (sensu Blake et al 2008) to movement, especially large rivers and unguarded roads, slow the spread of the disease by limiting great ape movements.…”

How should the psychological well‐being of zoo elephants be objectively investigated?

“…Thus, they show avoidance of roads [e.g. Blake et al, 2008] and of other areas or signs of human disturbance [Slotow, 2002;Blom et al, 2004]; they avoid walking uphill [Wall et al, 2006;Edkins et al, 2008;see Limin and Li, 2005 for similar findings for Asian elephants]; and they flee from the sounds of enraged bees [King et al, 2007], from hunts [Burke et al, 2008], and even from the odors of ethnic groups, Masai, who sometimes kill them [Bates et al, 2007; the sight of distinctive red Masai clothing, in contrast, elicits approach and attack]. In zoos, however, studies of preference or avoidance have been little used as yet [Mellor et al, 2007 give one preliminary example], but they could potentially be very valuable.…”