The Elephant Effect: What Birds and Bats Reveal About Ecosystem Change

This research brings together findings from a two-year initiative involving two BSc Wildlife Management Honours projects by Carina Meyer (2024) and Cameron McLean-Banks (2025), examining the ecological consequences of African elephant (Loxodonta africana) activity in the Timbavati Nature Reserve.

Undertaken as a joint project between Nelson Mandela University and the University of Pretoria, and supported by Timbavati management, the research focuses on how elephants alter vegetation structure and how these changes are reflected in bird and bat assemblages.

The project also includes the newly incorporated Schoongezight property, where fences were removed in March 2024. This created a unique opportunity to compare areas with long-term elephant occupancy in Timbavati with areas only recently exposed to elephant activity.

Elephants as Ecosystem Engineers

Elephants are regarded as ecosystem engineers because they change the physical structure of their environment.

In savanna systems, this occurs through stem breakage, uprooting, bark stripping, ringbarking, defoliation and pollarding. These processes can substantially alter the height, density and vertical arrangement of woody vegetation, changing the structural resources available to other species.

At sustained high levels of elephant use, these changes can reduce structural complexity and lead to a more homogenised vegetation state. In particular, elephant activity can reduce the upper woody strata, especially taller trees, while promoting coppicing and regrowth in the lower strata.

The result is often a shift from vertically complex woodland towards a more open and lower vegetation profile, with important consequences for habitat availability and niche space for species dependent on specific vegetation structures.

Why Birds and Bats?

Birds and bats are useful indicators of these changes because both groups respond strongly to vegetation structure.

Birds use different vegetation layers for feeding, nesting and refuge, while bats respond to the three-dimensional structure of vegetation through their flight and echolocation strategies.

By monitoring these groups, researchers can better understand how changes in vegetation influence biodiversity across the wider ecosystem.

What the Birds Revealed

The research suggests that patterns in bird species richness are broadly consistent with the Intermediate Disturbance Hypothesis.

Moderate elephant impact can create a patchwork of vegetation states, increasing habitat heterogeneity and supporting a wider range of bird species. This pattern was particularly evident in the Schoongezight area.

In contrast, areas experiencing higher elephant impact showed a shift in community structure, with fewer arboreal species and a greater dominance of terrestrial or herbivorous birds.

Over the 2024–2025 survey period, researchers recorded an overall reduction in bird species richness in Schoongezight, together with changes in community composition.

As taller canopy layers are removed, the diverse bird "patchwork" changes, often resulting in a greater dominance of terrestrial and herbivorous species over those associated with trees and woodland habitats.

What the Bats Revealed

Bats provided a valuable complementary measure because different foraging guilds respond to vegetation structure at different spatial scales.

Clutter-foraging species were negatively affected where canopy and understorey structure had been reduced.

Edge-space foragers, including many vespertilionids, appeared to benefit from the gaps and habitat edges created by moderate elephant activity.

Open-air foragers, such as molossids, which are generally less constrained by local vegetation density, also appeared to be affected where highly patchy vegetation reduced continuous foraging or commuting space. The shift in bat community composition was evident in the Schoongezight area, while the Timbavati sites displayed a comparatively stable community structure.

The Next Phase: Riverine Habitats

The next phase of the research will focus on riverine vegetation.

These areas are likely to show stronger elephant effects because elephant activity is not evenly distributed across the landscape. Elephants often concentrate near permanent water, and riverine zones contain plant species that are frequently targeted.

Riverine systems also support high plant diversity and complex vertical structure, making them important habitat for birds, bats and many other vertebrate species.

Information

Monitoring vegetation structure alongside bird and bat responses can help identify where elephant activity is maintaining valuable habitat heterogeneity, and where it may be reducing structural complexity or affecting sensitive ecological areas.

Research by Dr Mark Keith, University of Pretoria, in collaboration with Nelson Mandela University and supported by Timbavati Nature Reserve.

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