Pair of Eclectus parrots from Papua New Guinea, showing the species' striking sexual dimorphism. On the left, the female with bright red and blue plumage. On the right, the male with green plumage. // Credit: Shiny Things (Wikimedia Commons).

A recent study  led by the Doñana Biological Stations (EBD-CSIC) and conducted in Papua New Guinea provides new insights into the ecology and social structure of the Eclectus polychloros, one of the world's most singular parrot species. The findings confirm a marked imbalance between males and females in wild populations and support the hypothesis that this phenomenon is closely linked to its exceptional reproductive system.

The Papuan eclectus has fascinated evolutionary biologists for decades because it displays one of the most striking examples of sexual dimorphism among birds. While males are green, females have vivid red and blue plumage, a difference so pronounced that they were once considered separate species.

This pattern is closely related to the species' reproductive strategy. “Unlike most birds, females remain in the nest for long periods caring for their offspring, while several males compete to feed them. This reproductive system resembles cooperative polyandry, in which a female mates with multiple males and all of them contribute to raising the chicks,” explains Pedro Romero Vidal, researcher at the Doñana Biological Station.

Five males for one female

The study confirms that the population analysed shows a strongly male-biased sex ratio, with approximately five males for every female. This result is consistent with previous findings from the only Eclectus population studied in detail in Australia, suggesting that this pattern may be consistent throughout the species' distribution range. Furthermore, the data rule out the possibility that the observed imbalance is due to males being easier to detect during field surveys, reinforcing the robustness of the findings.

The study also provides the first systematic data from the core of the species' distribution, expanding knowledge beyond the peripheral populations that had been investigated previously.

Implications for evolution and conservation

The results support the idea that this unusual sex ratio is linked to the complex reproductive biology of the Eclectus and the processes of sexual selection that have shaped its evolution. However, the research team also suggests that it may be influenced by human activities, particularly poaching.

“In several regions of Papua New Guinea, females are more heavily targeted by poachers because of the high cultural value of their red feathers, which are traditionally used in ceremonial ornaments and clothing,” says Romero Vidal. “This selective harvesting could further intensify the imbalance between males and females observed in wild populations.”

Key information for protecting the species

Most Eclectus populations inhabit Papua New Guinea and neighbouring Indonesian islands, where the species faces increasing pressure from trapping for the wildlife trade and poaching. The research team highlights that understanding population structure is essential for designing effective conservation strategies.

“A sex ratio so strongly biased towards males, combined with the more frequent capture of females, could have severe negative consequences for the species' survival,” the researcher concludes.

This study represents a significant advance in our understanding of one of the most extraordinary social systems known among birds and provides new evidence to help guide conservation measures aimed at ensuring the long-term survival of the Eclectus parrot in its natural habitat.