Water Thick-knee

The water thick-knee (Burhinus vermiculatus) is a medium-sized African wader of the thick-knee family, about 38–41 cm long and weighing roughly 280–430 g. Its mottled brown plumage provides excellent camouflage, while the large yellow eyes are well suited to its mainly nocturnal lifestyle. It has a stout bill, long legs and conspicuously thickened ankle joints, the feature that gives thick-knees their English name.

Where ranges overlap, it can be confused with the Senegal thick-knee (Burhinus senegalensis) and Eurasian thick-knee (Burhinus oedicnemus). On the folded wing, the water thick-knee has a broad pale-grey panel with a narrow white bar above it and a darker bar above the white. The Senegal thick-knee lacks the distinct white bar, while the Eurasian thick-knee has a white bar bordered by dark bands both above and below.

The water thick-knee is strongly associated with water and occurs along riverbanks, lake shores, dams, estuaries, mangroves and other wetlands with exposed ground, sandbanks or sheltered margins. It uses both freshwater and coastal habitats and can also occupy artificial reservoirs where suitable shoreline remains available. Birds usually remain close to water even while feeding and are typically found within about 1 km of it.

Unlike many waders it is not restricted to open mudflats. Birds often rest among vegetation, rocks, driftwood or other cover immediately beside the water, where their cryptic plumage makes them difficult to detect during the day.

The diet consists mainly of small animal prey taken on or close to the ground. Insects such as aquatic beetles, grasshoppers and termites are important, together with crabs and other crustaceans, molluscs, worms, millipedes and other invertebrates. Frogs, tadpoles, small reptiles and occasional small fish may also be eaten.

Most feeding takes place from dusk through the night as birds walk slowly along shorelines and wetland edges, picking prey from the surface and shallow margins.

Water thick-knees are mainly nocturnal. During the day they usually rest quietly close to water and may remain almost motionless until activity increases toward dusk. They are nevertheless seen in daylight more often than many other thick-knees, especially in quiet areas with little disturbance.

Birds are usually encountered alone or in pairs and sometimes forage in small groups. At night they can reveal their presence with loud, far-carrying whistled calls even when the birds themselves remain difficult to see.

Breeding timing varies across the range and is often linked to local rainfall and water levels. Water thick-knees form monogamous pairs and nest on the ground, usually close to water. The nest is little more than a shallow scrape, sometimes placed beside a conspicuous object such as driftwood, a bush or animal dung.

One to three well-camouflaged eggs may be laid, and both adults take part in incubation. Incubation lasts roughly 22–25 days. The cryptic plumage of the adults and the mottled eggs make an exposed nesting site surprisingly difficult to detect. Development after hatching is poorly documented, but the young appear to fledge at about 60–63 days.

The water thick-knee is widespread across much of sub-Saharan Africa and is globally classified as Least Concern on the IUCN Red List. No major threat is known to affect the species across its entire range.

Wetland disturbance, shoreline development and changes to water levels can affect local populations, while artificial reservoirs may provide additional habitat where quiet banks and sufficient prey remain available.