Slaty egret’s shifting nesting sites offer clues to changing ecosystems

Scientists studying a rare African waterbird in Botswana’s Okavango Delta have found that previously established nesting sites are no longer being used, while new breeding locations have been identified, offering clues to how environmental changes may be affecting one of Africa’s most important wetland ecosystems.

The findings from surveys conducted in 2025 and 2026 show a changing pattern in the breeding distribution of the vulnerable slaty egret (Egretta vinaceigula), a small, shy wading bird found mainly in southern Africa.

Only about 3,000 slaty egrets are estimated to remain in the Okavango Delta, their principal stronghold.

Researchers found no nesting birds at a major breeding site in the western part of the Delta that had been examined in 2025. In the Jao Conservancy, two of four previously identified nesting sites had also disappeared.

One site had been affected by fire, while another was damaged after elephants used the area to cool themselves following a summer heatwave.

But the surveys also revealed new nesting locations elsewhere in the Delta, including an island concealed by vegetation where researchers found three bluish eggs.

The contrasting findings suggest that the birds may be changing where they breed as conditions in the wetland shift. Researchers say, however, that further observations are needed to determine whether the changes reflect a longer-term pattern and what they mean for the species’ population.

A sensitive indicator of environmental change

A senior wildlife biologist with Botswana’s Department of Wildlife and National Parks, Monei Onalethatai, said the slaty egret was particularly sensitive to disturbances and changes in its surroundings.

“The slaty egret is so sensitive to environmental disturbances and to ecosystem changes. “Whatever happens in the ecosystem will necessarily reflect in the distribution and the presence of the bird,” she said.

The bird’s restricted range makes these observations particularly important to conservationists seeking to understand changes in the Okavango Delta.

Executive Officer of the Agreement on the Conservation of African-Eurasian Migratory Waterbirds (AEWA), Sergey Dereliev, said the species was endemic to southern Africa, with its distribution concentrated in the Okavango Delta and neighbouring floodplains.

He said the bird could be found in the Delta and adjacent floodplains in the Okavango and Zambezi river basins.

*“*The slaty egret is a long-legged wading bird which is endemic to southern Africa, and its uniqueness lies in the fact that it’s only possible to see this bird in the Okavango Delta and some adjacent floodplains in the Okavango and Zambezi river basins.”

Researchers are monitoring its population and breeding success to improve understanding of the pressures affecting the species and its habitat.

How water shapes breeding conditions

The Okavango is an inland delta whose waters never reach the ocean. Floodwaters originating from rainfall in Angola’s highlands flow south into Botswana, spreading across a network of channels, floodplains, lagoons and islands before eventually evaporating or disappearing into the Kalahari.

The annual flood, which typically flows through the Delta between June and August, helps determine the availability of water and habitat for wildlife.

According to the United Nations, the seasonal flood pulse supports more than 400 bird species, including migratory birds arriving from Europe and northern Asia. Some use the Delta as a stopover during longer journeys, while others remain through the northern winter. Zebras, buffalo, elephants, wildebeest and numerous fish species also depend on the wider ecosystem.

For the slaty egret, the extent of flooding can influence breeding conditions. The birds tend to nest on islands or in areas surrounded by water, which help protect them from disturbances.

Changes in water levels can affect the availability of suitable nesting locations, while vegetation, food supplies and disturbance can determine whether a particular site remains suitable for breeding.

In 2026, the Okavango experienced an unusually large flood. Researchers had expected the additional water might allow slaty egrets to expand their breeding grounds into new areas.

The findings, however, presented a more complicated picture. Some established nesting sites were empty or had disappeared, while new sites were found elsewhere.

The observations suggest that the relationship between flooding and breeding habitat may change conditions across the Delta without making every location suitable for nesting.

Why repeated surveys matter

Researchers have used satellite imagery and field observations to identify breeding locations and examine how vegetation, water availability and habitat conditions relate to the birds’ distribution.

The latest surveys have highlighted the need to revisit known nesting sites while searching for previously unrecorded ones.

Scientists are still collecting evidence and say the available observations are insufficient to establish a population trend or identify a single cause for the changes in breeding distribution.

Repeated monitoring will be needed to determine whether the birds are making temporary adjustments to changing conditions or whether their movement away from established nesting sites represents a more persistent pattern.

The findings also underline the importance of looking beyond individual breeding colonies. A site that was suitable in one year may no longer support nesting in another, while a previously overlooked location may become important under different conditions.

The slaty egret’s distribution could therefore provide useful evidence of environmental changes across the Delta, although researchers need further data to establish how closely particular changes in the bird’s breeding patterns correspond with changes in the wider ecosystem.

Protecting the species also requires cooperation between countries that share the river systems on which its habitat depends. Climate change and water management across national borders can affect the availability and distribution of water, making regional collaboration important for wetland conservation.

For researchers, the disappearance of a nesting colony deserves attention even when birds are found elsewhere. Likewise, the discovery of a new colony is important without necessarily indicating that the species is thriving.

Understanding why these locations become suitable or unsuitable over time could help scientists assess the pressures facing the slaty egret and guide efforts to protect the Okavango Delta’s wildlife and habitats.