Adult sex-ratio and group size of the cooperative breeding eclectus parrot in Papua New Guinea

Eclectus parrots stand out as an intriguing case within the avian realm, showcasing exceptional characteristics such as inverse sexual dimorphism, marked sex ratio bias, and cooperative breeding—features uncommon among parrots and birds in general. Notably, the population of the Papuan eclectus (Eclectus polychloros) exhibits a skew towards a higher proportion of males, a phenomenon believed to be consistent across this and the other eclectus species’ range. However, given that existing data pertains to a singular population, comprehensive investigations across diverse Papuan eclectus populations throughout their range are compelling for a thorough understanding of the intricate reproductive mechanisms of this distinctive parrot species. For this purpose, we conducted road surveys combined with foot transects and observation points across three different areas of Papua New Guinea. We counted the number of individuals observed together and attempted to identify their sex, recording the method of detection and the detection distance for each individual. Group size varied between 1 (74.63% of the instances) and 6 individuals (mean = 1.53, N = 68), and most of the groups were composed only by males. The sex-ratio observed among groups was 5:1 biased towards males (70 males, 14 females). Females were easier to detect by sight and at larger distances than males. However, these differences were not statistically significant, suggesting that the observed sex-ratio was not strongly influenced by detectability biases. In this context, we contribute valuable insights into the adult sex ratio and group size of Papuan Eclectus parrots within their natural habitat in Papua New Guinea.