Distribution and habitat
The water thick-knee has a widespread distribution in sub-Saharan Africa, being found in Angola, Botswana, Burkina Faso, Burundi, Cameroon, Central African Republic, Republic of the Congo, Democratic Republic of the Congo, Eswatini, Ivory Coast, Ethiopia, Gabon, Ghana, Kenya, Liberia, Malawi, Mozambique, Namibia, Niger, Nigeria, Rwanda, Senegal, Somalia, South Africa, Tanzania, Uganda, Zambia, and Zimbabwe.
Across its range it is found on the edges of lakes, estuaries and rivers, as well as mangroves and also some sheltered beaches. It also needs bushes or nearby woodlands for shelter. It is found from sea-level to 1,800 m (5,900 ft).
The water thick-knee is 38 to 41 cm (15–16 in) and weighs 293–320 g (10.3–11.3 oz). It has a heavy bill that is black with yellow at the base. The wings are broad and blunt and the tail is short.
The water thick-knee is a terrestrial feeder that forages at night. Although it is typically associated with water it can be found foraging up to 1 km (0.62 mi) from water. It feeds on insects, crustaceans and mollusks.
The water thick-knee generally breeds in the dry season or early rainy season. It is a monogamous breeder with both parents guarding the nest and brooding the eggs. The nest is a simple scrape in sandy or stony ground, usually close to water. The clutch size is two sandy-yellow eggs. Both sexes incubate the eggs for 22-25 days, and both are responsible for feeding the young. Unique among birds, thick-knee pairs frequently nest adjacent to and sometimes directly on top of Nile crocodile nests. The two species share a form of symbiotic mutualism with the more energetic and vocal thick-knee functioning as loud sentries for the nests as the more powerful crocodile provides protection. Should a nest raider approach, the thick-knee pair will spread their wings in a threat display and harass and peck at the intruders to drive it off. If the pair not be successful, the mother crocodile will be drawn in by their continued calls and arrive.
- BirdLife International (2016). "Burhinus vermiculatus". IUCN Red List of Threatened Species. 2016: e.T22693584A93413917. doi:10.2305/IUCN.UK.2016-3.RLTS.T22693584A93413917.en. Retrieved 12 November 2021.
- Hume, R; Kirwan, G. M. (2019). del Hoyo, Josep; Elliott, Andrew; Sargatal, Jordi; Christie, David A; de Juana, Eduardo (eds.). "Water Thick-knee (Burhinus vermiculatus)". Handbook of the Birds of the World Alive. Barcelona: Lynx Edicions. Retrieved 11 February 2019.
- Water dikkop/Water thick-knee - Species text in The Atlas of Southern African Birds.