Heterospecific competition in a threatened cavity-nesting parrot: a case study of the eastern Regent Parrot (Polytelis anthopeplus monarchoides).

Nest cavities are a limited resource, given the extensive land clearance that has occurred in Australia. Some obligate cavity-nesting birds are vulnerable to extinction and experience risk from heterospecific species that compete for limited nest cavities. The aim of this study was to identify intruder bird species at nest cavities of a threatened eastern subspecies of Regent Parrot (Polytelis anthopeplus monarchoides), and to measure the impact of intruder birds on parental care (parental time budgets) and nesting outcome (nest usurpation). We observed 25 eastern Regent Parrot nests using a combination of 608 h of video recording and 67 h of binocular observation. In total, we observed 16 heterospecific bird species at the nest entrance of the eastern Regent Parrot. Two of these species were examined for their impact on parental care behaviour. The presence of Noisy Miners (Manorina melanocephala) near the nest cavity increased the time that Regent Parrots spent at the nest cavity entrance. The number of Yellow Rosella (Platycercus elegans flaveolus) visits to the nest cavity predicted nest usurpation. Nest usurpation of a Regent Parrot nest occurred in 6/25 cases (24%), of which 5/6 nests were usurped by Yellow Rosellas. Understanding heterospecific competition for nest cavities in eastern Regent Parrots should inform targeted conservation measures. [ABSTRACT FROM AUTHOR]