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Abstract: Pacific imperial pigeons (Ducula pacifica) are important seed dispersers with complex vocal and behavioural repertoires. This study documents their vocalisations, territoriality, mating, nesting, and feeding behaviours in Rarotonga, Cook Islands. Five vocalisation types were identified and described here as the common coo, territorial coo, courtship coo, quiet coo, and growl. The common coo and growl were most frequent, often exchanged in call-and-response between distant birds. The territorial coo and courtship coo were linked to close interactions. Territoriality involved displays, chasing, and occasional combat. Year-round aerial display flights suggest a potential role in territoriality rather than being exclusively tied to breeding season. Mating included novel post-mating courtship feeding. Feeding observations and faecal analyses confirmed an exclusive reliance on non-native plants, indicating a potential role in spreading invasive species. This study enhances knowledge of Pacific imperial pigeon vocalisations and behaviours, with implications for species identification, invasive species management, and habitat maintenance and restoration in Pacific ecosystems.