African Darter (Anhinga rufa)

Cover image of African Darter by Graeme Hatley – Stanford, Western Cape – BirdPix No. 285516

Darters belong to the Family: ANHINGIDAE. Anhingas and darters are large water birds with long, slender necks, short legs, long pointed bills and long tails. Males and females are the same size. Anhingas and darters are typically brown or black in colour. The family comprises a single genus with 4 recognised species. Their closest relatives are gannets, then cormorants and herons.

Identification

The African Darter is a large, conspicuous and distinctive water bird. It is a large, cormorant-like bird, with a dagger-like bill and a very long, slender neck.

The sexes differ slightly in breeding plumage coloration. The adult breeding male has a rufous-chestnut fore neck and upper breast. The head is relatively small and has a white stripe that extends from below the eye, across the cheek and down the neck. The chin is cream-coloured and the lower breast and belly is blackish-brown. The upper parts are dusky-brown with elongate white-striped scapulars and wing coverts. The flight feathers and underwings are black. The tail is rounded or wedge-shaped and relatively long. Adult breeding females differ slightly from breeding males, having a paler brown crown and neck. The cheek stripe is cream (not white) and is less well defined.

In both sexes the bill is yellowish horn-grey to greenish horn-grey. The eyes are usually golden yellow, but are sometimes brown or red. The legs and feet are pale to dark brown and the feet are totipalmate (fully webbed).

Non-breeding adults are paler, duller and browner than breeding adults, especially on the neck and mantle. At this time the white cheek stripe is reduced and less conspicuous.

Juveniles resemble the adult female, but have pale buffy brown underparts. The bill is grey-green and the facial skin is dark green.

The African Darter is unlikely to be mistaken for another species. It is most similar to Cormorants and the African Finfoot (Podica senegalensis). Cormorants have shorter, thicker necks and hook-tipped bills. The African Finfoot is easily recognised by its red bill (dark in juveniles), legs and feet.

Status and Distribution

The African Darter is generally a locally common resident with some local movement in the non-breeding season.

It is widely distributed in sub-Saharan Africa, Madagascar and parts of the Middle-East, occurring wherever there is suitable aquatic habitat. The African Darter is widespread in southern Africa but is localised in the arid west, where it is confined to large rivers and dams. It avoids the driest parts of the Northern Cape, Botswana and Namibia where surface water is scarce, and is also largely absent from the Lesotho plateau.

The range of the African Darter has increased across southern Africa due to the construction of dams and their stocking with fish. However, in some areas the African Darter is impacted by the loss and degradation of wetlands and river systems. It is sometimes seen as a pest at fish farms and trout dams where it may be illegally persecuted, but this impact is considered minimal.

Habitat

The African Darter inhabits still and slow-moving freshwater bodies with open water like lakes, dams, rivers and sewage ponds. It is scarce in turbulent water, fast-flowing rivers and in areas with dense floating vegetation. Prefers places with dead trees, rocks or banks where it can rest after feeding. The African Darter also forages in estuaries and coastal lagoons but typically avoids other marine habitats.

Behaviour

The African Darter can be somewhat gregarious when feeding but may also be encountered solitarily.

Sits very low in the water, typically with only the neck and head protruding, snake-like above the surface, hence the colloquial name of ‘Snakebird’. Rarely sits higher in the water with the upper parts exposed. Dives by thrusting forward like a cormorant and glides smoothly through the water, barely leaving a ripple. Enters the water silently, direct from their perch, but can also land on water, using the feet as brakes.

The African Darter is well adapted to spending time underwater. The body plumage is very absorbent and its bones are more solid, containing less air than in similar diving birds like cormorants, resulting in reduced buoyancy. The African Darter is neutrally buoyant underwater at a depth of around 3 meters. The feet are fully webbed and the legs are set far back to aid propulsion under water. The flight feathers are waterproof, allowing the African Darter to fly even when completely drenched. However, they prefer to perch on a dead tree or rock after foraging to allow the body feathers to dry off. They typically sit with their wings spread for up to 1.5 hours, raising the body feathers and orienting the body towards the sun. They sometimes beat their wings slowly to accelerate drying or to generate body heat. Several individuals may aggregate at favoured resting sites. They gular-flutter to cool down During hot weather. This is achieved by frequently vibrating the throat membranes, which increases airflow resulting in improved evaporation.

The African Darter roosts communally at night, usually in trees or large reedbeds. They mostly roost close to their feeding areas, but will sometimes commute up to 10 km, either singly or in loose groups. They fly well, with regular flaps and glides, and does not fly in formation like many other water birds. The neck is extended in flight, showing a characteristic kink. The African Darter soars from time to time, somewhat resembling a long-necked raptor.

The African Darter feeds mostly on fish but also takes frogs, tadpoles and aquatic arthropods. They are non-selective regarding fish prey, consuming a wide range of suitably sized species. In some places where fish are absent, like on farm dams in the Karoo, they feed almost exclusively on frogs and large tadpoles.

The African Darter forages at depths of up to 6 meters, mostly in the mid-water or along the bottom. Dives usually last for 30 to 100 seconds, increasing in duration with water depth. They hunt using stealth, preferring to ambush prey rather than chase it down. As they are neutrally buoyant underwater, they are able to wait motionless while suspended in the midwater, wings half open. Prey is speared by rapidly thrusting the neck forwards. The neck is flexible with a special hinge mechanism between the 8th and 9th vertebrae. Prey is speared with the bill slightly open. Small prey is mostly speared with the upper mandible while larger prey items are impaled with both mandibles.

Captured prey is brought to the surface where it is tossed in the air and caught in the bill before being swallowed head first. Some small prey may be swallowed underwater. Prey is swallowed head first to prevent sharp fin spines from snagging in the throat. Occasionally catches prey too large to swallow, and after a struggle, is eventually abandoned. After feeding they usually wash their face and bill by wiping them against the feathers on their backs.

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The African Darter is monogamous and breeds mainly in the spring and summer months (September to March) in South Africa. They usually breed colonially, often with other water birds like White-breasted and Reed Cormorants, African Spoonbills and herons.

The nest is a fairly large untidy platform of sticks or dead reeds, with a shallow bowl lined with grass. Built in tree fork, often over water or on island; also in large reedbed. Pairs work together to construct the nest. The male collects the nesting material and the female weaves it into the nest. The nest site and nesting material is fiercely guarded against other birds that may attempt to steal nest material. The nest is sometimes completed in as little as 1 day, but the pair will continue to add material during incubation and early chick rearing. The African Darter usually builds a new nest at the start of each breeding season.

Eggs are laid throughout the year in north-eastern South Africa, Botswana and Zimbabwe with slight peaks in spring and late summer. Egg laying is mainly from October to December in south-eastern South Africa and between August and October in the Western Cape.

Clutch size ranges from 2 to 7 greenish white eggs. They are laid at irregular intervals and incubation starts with the first-laid egg which leads to asynchronous hatching. The incubation period takes 21 to 27 days to completion and duties are shared by both sexes. The African Darter lacks a brood patch and so incubates with the feet. Incubation shifts are fairly short, with several changeovers per day.

The newly hatched young are altricial and hatch out naked with their eyes closed. White down begins to show on their bodies after 2 days. Chicks are fed by both parents, initially by regurgitation, thereafter the chicks insert their heads into the adult’s throat to take food stored in the adults crop. Adults also bring water to the chicks in hot weather. Young birds leave the nest at 5 to 6 weeks old and are fully fledged at 7 weeks.

The African Darter has a recorded lifespan of at least 12 years.

Further Resources

Species text from the first Southern African Bird Atlas Project (SABAP1), 1997.

The use of photographs by Anthony Paton, Bryan Groom, Corrie du Toit, Gregg Darling, Kevin Lavery, Les Underhill, Mark Stanton, Terry Terblanche, Tony Archer and Werner Van Goethem is acknowledged.

Virtual Museum (BirdPix > Search VM > By Scientific or Common Name).

Other common names: Darter (Alt. English); Slanghalsvoël (Afrikaans); lvuzi (Xhosa); Afrikaanse Slangenhalsvogel (Dutch); Anhinga roux, Anhinga d’Afrique (French); Schlangenhalsvogel (German); Mergulhão-serpente (Portuguese)

A list of bird species in this format is available here.

Recommended citation format: Tippett RM 2024. African Darter Anhinga rufa. Biodiversity and Development Institute. Available online at https://thebdi.org/2024/08/13/african-darter-anhinga-rufa/

Bird identification, birding