AbstractParent birds are often assumed to regulate the amount of their nest material during incubation in response to various costs and benefits. This assumption, however, is rarely tested. We investigated this assumption in a ground-nesting shorebird, the Kentish plover (Charadrius alexandrinus) by experimentally manipulating the amount of nest material. Materials were removed from some nests (reduced nests) and added to other nests (increased nests), whereas in control nests the amount of nest material was not manipulated. In both reduced and increased nests the parents restored the original amount of nest material within 24 hours. The parents tended to spend more time on arranging nest material in both reduced and increased nests than in control nests. However, neither incubation behaviour nor internal egg temperatures were different between reduced, increased and control nests. We conclude that Kentish plovers can quickly adjust the amount of materials around their eggs. This suggests that the parents carefully balance the various costs and benefits of nest material use during incubation.
