Second-hand housing: a review of avian species using Hamerkop nestsfor breeding

Nest-building is an energetically expensive activity for birds. Consequently, some species opportunistically use other species’ nests. The Hamerkop <i>Scopus umbretta</i>, an endemic sub-Saharan African waterbird, constructs one of the largest nests of any bird in the world. Little is documented on the role of Hamerkop nests in the breeding biology of other avian species. Therefore, we assessed this from the literature and first-hand observations to determine which species use Hamerkop nests and their associated behaviours. We found at least 20 avian species using Hamerkop nests for breeding in 18 African countries. The Barn Owl <i>Tyto alba</i> was the most commonly reported species using Hamerkop nests. Six species actively usurp nests from Hamerkop pairs. Nine species nested inside the nest chamber, and eight nested on top of the structure. This highlights the role of Hamerkop nests in other avian species’ breeding.