How artificial nests, long-term science and cooperation across the Greater Kruger are changing the future of one of South Africa’s most threatened birds
Before sunrise, a low, resonant call rolls across the bush. It can travel for kilometres and is often felt before its source is seen.
The voice belongs to the Southern Ground-Hornbill, an unmistakable bird standing almost a metre tall, with black plumage, a heavy bill and vivid red facial skin. Its imposing appearance hides a more vulnerable reality. Southern Ground-Hornbills reproduce exceptionally slowly and are classified as regionally Endangered in South Africa.
At Thornybush Nature Reserve, one active natural nest and one artificial nest site form part of the long-running APNR Southern Ground-Hornbill Project.
What is the APNR Southern Ground-Hornbill Project?
The APNR Southern Ground-Hornbill Project is a research and conservation programme established in 2000 across the Associated Private Nature Reserves, or APNR.
The APNR (Associated Private Nature Reserves) brings together five private nature reserves on the western boundary of Kruger National Park: Thornybush, Klaserie, Timbavati, Umbabat and Balule. With internal fences removed, wildlife can move through this connected Greater Kruger landscape.
Working with the University of Cape Town’s FitzPatrick Institute of African Ornithology, the project monitors Southern Ground-Hornbill groups, studies their behaviour and breeding success, and provides artificial nesting sites where suitable natural cavities are scarce.
A bird that depends on its family
Southern Ground-Hornbills are the world’s largest cooperatively breeding birds. They usually live in groups consisting of a dominant breeding pair and several helpers, often male offspring from previous breeding seasons.
Every member of the group has a role. Together they defend a large territory, forage, watch for danger and provide food for a nesting female and her chick.
The female generally lays two eggs, several days apart. Because the first chick hatches earlier and develops faster, the second seldom survives. The remaining chick stays in the nest for approximately 80 to 90 days, relying on the entire group for food.
Even after fledging, survival is not assured. Southern Ground-Hornbills mature slowly, occupy territories that can extend across hundreds of square kilometres and may take years to raise another chick successfully.
According to BirdLife South Africa’s 2025 assessment, fewer than 2,500 mature Southern Ground-Hornbills remain in the region. Their slow rate of reproduction makes every successful nest important.
Why artificial nests matter
Southern Ground-Hornbills require large, deep cavities in mature trees, rock faces or earth banks. Across much of their former range, these nesting places have disappeared as landscapes have changed and large trees have been lost.
The APNR Southern Ground-Hornbill Project currently monitors approximately 35 nesting sites. Only five are natural. The remainder are specially designed artificial nests.
These are more than simple wooden boxes. Their position, internal temperature, durability and suitability for growing chicks all matter. Researchers inspect, repair and improve the structures while monitoring breeding attempts and the development of nestlings.
The results have been significant. Southern Ground-Hornbill groups in the APNR now breed successfully approximately once every three years, compared with an interval of around nine years recorded in Kruger National Park. The study population is estimated to have roughly tripled during the project’s first 25 years.
Thornybush’s place in the wider recovery
Thornybush Nature Reserve contributes two important sites to the APNR monitoring network: one active natural nest and one artificial nest.
Each site adds to a much larger body of information. Nest observations help researchers understand when breeding begins, how chicks develop, whether groups return to the same territory and how changing environmental conditions affect breeding success.
This is the distinction that matters: the work at Thornybush does not happen in isolation. It forms part of a coordinated conservation effort operating across five connected nature reserves and supported by decades of specialist research.
Success for one group can eventually strengthen the population beyond its original territory. In one recorded example, a ringed bird that fledged within the APNR in 2011 later dispersed approximately 40 kilometres and joined a new breeding group outside the original study area.
The science inside the nest
The project’s collaboration with UCT’s FitzPatrick Institute of African Ornithology allows researchers to look beyond the number of chicks fledged.
Temperature sensors placed inside nests record conditions throughout the day. Camera traps document feeding behaviour, while measurements taken at different stages reveal how quickly nestlings are growing and whether excessive heat is affecting their physical condition.
Researchers are also studying how adult birds balance feeding, vigilance and the need to seek shade during periods of extreme heat. This work is informing the design and placement of future artificial nests, including structures that provide better protection from rising temperatures.
Long-term monitoring is particularly important for a bird that may live for 50 to 60 years. Meaningful patterns only become visible when the same groups, territories and breeding sites are studied across many seasons.
From research to national recovery
Information gathered in the APNR contributes to South Africa’s Southern Ground-Hornbill Species Action Plan and Reintroduction Plan.
The project also supports the Mabula Ground-Hornbill Project, which works to establish new breeding groups in parts of the species’ former range. Under carefully managed specialist protocols, second-hatched chicks that would not ordinarily survive in the wild can be collected, reared and later considered for reintroduction.
This connection between field research, active nest management and wider reintroduction work makes the APNR population important far beyond the boundaries of the five participating reserves.
More than one successful nest
The recovery of the Southern Ground-Hornbill cannot be measured through a single breeding season.
It is measured in artificial nests maintained through summer heat, chicks monitored from hatching to fledging, movements recorded years later and knowledge shared across reserve boundaries.
At Thornybush Nature Reserve, one natural nest and one artificial nest may represent two small points on a much larger map. But for a species that reproduces this slowly, each viable nesting place offers something immensely valuable: another opportunity to raise the next generation.
The deep call heard across Thornybush at dawn is more than one of the defining sounds of the bushveld. It is evidence that space, science and sustained cooperation can still change the course of a species.
