The Slaty Egret – Okavango’s special bird
The Slaty Egret is a globally threatened bird that is virtually confined to the Okavango Delta. For this reason, Batswana have a special responsibility to protect the species – and BirdLife Botswana has a vital role to play in monitoring its population and advocating conservation measures that will ensure its continued well-being.
The Slaty Egret is not an obscure or difficult-to-see species. It is about the size of the well-known Black Heron, but is slaty grey in colour. Until fairly recently, the Slaty Egret and Black Heron were thought to be variants of the same species - however, in the case of the Slaty Egret, the legs are yellow, and this distinguishes it from the Black Heron which has black legs and bright yellow feet. A further less obvious feature to look out for is the vinous/brown throat of the Slaty Egret, which extends down right onto the belly in immature birds.
The characteristic behaviour of the Black Heron of ‘mantling’ its wings over the water when fishing, is not displayed by the Slaty Egret.
BirdLife Botswana/Department of Wildlife and National Parks study
A BirdLife Botswana team, in conjunction with the Botswana Department of Wildlife and National Parks, undertook a one-year baseline survey of the Slaty Egret in 2005, covering the Okavango Delta Ramsar site – at 60,000 km2, the largest Ramsar site in the world.
Despite the logistical difficulties of studying the bird, useful data were gathered on its distribution and habitat usage, and feeding areas and behaviour. The Slaty Egret is essentially a bird of shallow seasonal floodplains that have short, emergent vegetation - as such it is quite widespread throughout the Delta where this habitat occurs. The availability of this habitat is increased by fire and high grazing pressure (particularly from Lechwe), both of which reduce grass height.
The Slaty Egret spends most of its time during the day on these floodplains actively foraging for small fish - primarily juvenile Cichlids (bream) - frogs and aquatic invertebrates which it locates by sight in the clear, shallow water. Although the availability of prey items is high, there is high competition for this food resource among Slaty Egrets, and between Slaty Egrets, other herons, Spoonbills and Sacred Ibis.
Slaty Egret breeding habitat is quite different from the habitat used for feeding – they prefer dense reedbeds, but smaller numbers will also use Water Fig islands and Phoenix Palm islands. The nest is an untidy platform, typical of egrets and herons, and the light blue eggs are indistinguishable from those of closely related species. Eggs are laid at daily intervals, and since incubation commences immediately the first egg is laid, chicks hatch at daily intervals after some 23 days. The young are soon able to leave the nest and clamber around in its vicinity before they can fly.
This ecological information will contribute towards an understanding of the actual and potential threats to this special bird. Researching its ecological requirements is the first step towards protecting and conserving it. The information is currently being incorporated in the Okavango Delta Management Plan and it is hoped that in this way, the few known breeding sites for this species, which are crucial for its survival, will be protected.
The next step is to incorporate the information gathered into a Slaty Egret Action Plan that will guide the birds’ conservation by addressing any potential threats. This is currently underway. BirdLife Botswana also continues to monitor the population size by conducting regular counts along fixed routes (transects) where suitable habitat for the bird exists.
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