The behavioural shifts of the Slaty Egret (Egretta vinaceigula), a small, shy water bird mainly found in Botswana’s Okavango Delta, are an important instance of changes in natural ecosystems, United Nations Environment Programme (UNEP) officials said recently.
Only around 3,000 Slaty Egrets are estimated to remain in the Delta, its principal stronghold.
“The Slaty Egret is so sensitive to environmental disturbances and to system changes,” Monei Onalethata, a senior wildlife biologist with Botswana’s Department of Wildlife and National Parks, said in a UNEP statement issued in the backdrop of World Migratory Bird Day themed around “Every Bird Counts – Your Observations Matter!”,
“Whatever happens in the ecosystem will necessarily reflect in the distribution and the presence of the bird,” Onalethata added.
Unlike other major deltas, Okavango is an inland delta whose waters never reach an ocean. Floodwaters from rainfall in the Angolan highlands travel southwards into Botswana, expanding into a maze of channels, floodplains, lagoons and islands before the water eventually evaporates or disappears into the Kalahari desert.
Hence, the extent of annual flood influences the Delta and closely affects the breeding behaviour of the Slaty Egret.
The birds nest on islands or places surrounded by water to avoid disturbances, helping researchers identify places preferred by them.
“The Delta’s annual flood flows down between June and August from rains in Angola’s highlands, creating a seasonal pulse that sets the rhythm of life for a multitude of animals and more than 400 species of birds from Africa and around the world. These birds, some from as far away as Europe and northern Asia, fly to the Delta each year, some using it as a stopover during a longer journey south, and some remaining for the duration of the northern winter. Migratory herds of zebras, buffalo, elephants, wildebeest and various fish also freely move through the Delta from surrounding countries,” the UN noted.
This behaviour has an important advantage for ecological monitoring. Scientists found from satellite images how change in vegetation, food and water availability with undisturbed habitat enables the bird to breed and thereby serves as a biological indicator of the ecosystem.
In 2025, researchers and local conservationists embarked on a survey of the species and returned in 2026 to assess breeding areas, some of which were not included in the previous trip, which revealed a mix picture.
The researchers observed that the main breeding site examined in 2025 in the western part of the Delta had no bird nesting and their numbers had also diminished.
For instance, in the Jao Conservancy, two of four former nesting sites had disappeared - one was affected by fire, while another was damaged after elephants used the area to cool themselves following a summer heatwave.
However, the researchers found new nests in other parts of the delta — indicating that birds may be using other parts of the Delta as conditions change.
This was established with three bluish eggs found on an island hidden in a vegetation.
These observations become important as the Okavango experienced an unusually large flood this year.
Considering the changing situation, researchers had expected that the greater flood might allow Slaty Egrets to expand their breeding grounds into new areas.
However, the situation was complex as previously known breeding spaces were empty while previous nesting sites were lost, and new sites were found in places not known before.
The researchers concluded that the birds are responding to multiple changes in their surroundings primarily — water, nesting vegetation, disturbance and the availability of suitable habitat.
It showed that a change in one part of the system can alter how those conditions come together at a particular site.
However, the researchers are still in the process of collecting evidence, and the latest observations is inadequate to establish a population trend or identify a single cause for the changes in breeding distribution.
The researchers now underline that repeated observations are crucial to understand the shifting breeding sites pattern and understand how these birds choose to live and breed and why they stop returning to conventional breeding sites.
They note that the bird becomes an early warning system, helping to understand aspects of its protection and its habitat.
The UN stated that against this moving background, the location of a breeding colony is not just a point on a map. It becomes an observation about the conditions that made that location suitable—or unsuitable—for a particular species at a particular moment.
And hence the disappearance of a breeding site deserves attention even when the birds may turn up somewhere else.
It is also why the discovery of a new nesting site matters without necessarily signalling recovery, the UN observed.
