Topic : Land Birds
Article 10 
20 December 2006
Thick-knee — bill size difference
Water thick-knees have larger and more robust bills that Spotted Thick-knees.
The proportionally larger bill size in Water Thick-knee Burhinus vermiculatus reflects prey preference of this aquatic margin species. Crabs and other crustaceans make up a high proportion of prey and crabs with up to 50 mm carapace size are fed on. Other prey includes frogs, grasshoppers, termites and worms.
Spotted Thick-knee Burhinus capensis on the other hand feeds predominantly on smaller prey, mainly in the form of insects such as beetles and termites.
In the non-breeding season, Spotted Thick-knees may form large daytime roosts where these birds sleep with legs tucked under the body and heads resting on the ground.
Being predominantly nocturnal, the exceptionally large, almost umbrella-like eyelids help shade their large eyes from the glaring sun when they roost during the day. This shaded effect also helps when looking out for intruders in the bright glare of the daylight sun.