Abstract
Avian brood parasites occasionally interact with alternative hosts, providing valuable insights into their behavioral flexibility under atypical environmental conditions. The great spotted cuckoo (Clamator glandarius) typically targets medium-sized tree-nesting corvids in wooded landscapes. Here, we report records of great spotted cuckoo parasitism on the red-billed chough (Pyrrhocorax pyrrhocorax), a cavity-nesting species foraging in open montane, coastal and pseudo-steppe landscapes that has recently adopted anthropogenic structures for nesting in farmland. Across these treeless environments, where primary cuckoo hosts are scarce or absent, we recorded a parasitism event using an artificial nesting site inside an abandoned rural building in Los Monegros (Ebro Valley, northwestern Spain) that resulted in the successful fledging of three great spotted cuckoo chicks. These observations illustrate a striking sequential behavioral cascade of innovations where the parasite successfully tracked a host’s novel nesting shift in artificial structures, enriching our understanding of the ecological breadth and behavioral adaptability of avian brood parasites.