The Eclectus parrot, a jewel of the Australasian rainforest canopy, captivates with its striking appearance and peculiar behaviors, setting it apart in the avian world. Most renowned for their extraordinary sexual dimorphism, Eclectus males boast vibrant emerald green plumage, while females display a stunning contrast of dark ruby red, often accented with violet or cobalt feathers. This dramatic difference, so pronounced that early biologists initially mistook them for separate species, highlights a fascinating evolutionary puzzle. While sexual dimorphism is present in many parrot species, the Eclectus exhibits an extreme divergence where chicks are easily sexable by their developing plumage—green for males, red for females—from an early stage. Unlike many sexually dimorphic species where males develop their adult colors gradually, Eclectus chicks display their species-specific coloration remarkably early.
The visual disparity between male and female Eclectus parrots challenges conventional understanding, where typically the male exhibits more flamboyant traits, as seen in peacocks. However, in Eclectus, neither sex is inherently less colorful, though the female’s red plumage makes her more conspicuous. This distinct coloration eluded explanation by even prominent evolutionary biologists, including the late Dr. Bill Hamilton, who famously used a slide of a male and female Eclectus in lectures, stating that understanding their color difference would be his final biological pursuit. [cite:0, cite:1]
The enigma surrounding Eclectus coloration spurred Dr. Robert Heinsohn of the Australian National University to initiate a long-term study in 1997. Drawn by the unsolved mystery highlighted by Dr. Hamilton, Dr. Heinsohn recognized the Eclectus parrot’s unparalleled sexual dimorphism as a unique biological puzzle ripe for investigation. The challenges of studying these birds in their natural habitat are considerable. Eclectus parrots typically nest high in trees, averaging 22.2 meters above the ground, with nest holes often spaced widely apart—approximately one suitable nest hole per square kilometer in Australia. [cite:2, cite:3] This necessitates extensive travel through dense rainforests and arduous climbs up towering trees in oppressive heat and humidity for any biologist undertaking fieldwork.
Dr. Heinsohn and his team navigated these difficulties, locating forty Eclectus nests within their initial field seasons in the dense rainforests of Australia’s Cape York Peninsula. Their research methods involved arduous treks along creek beds and ridge lines. The birds’ vocalizations near nests could aid in spotting them, though they often took flight upon sensing human presence. Aerial surveys also proved useful in identifying potential nesting sites in tall, emergent trees.
Accessing nests, typically 15-30 meters high, required the use of single rope techniques for climbing. Researchers collected small blood samples from nestlings and shed feathers for DNA analysis. Dr. Heinsohn estimates his climbing efforts equate to ascending a tree ten times the height of Mount Everest. Capturing adult males for banding proved equally challenging, necessitating mist nets deployed about thirty meters above the ground. Handling these parrots, known for their strong bites, added to the difficulty. Observation blinds were erected 20 meters high in trees to allow for unobtrusive study of the birds.
The data gathered through these demanding efforts began to demystify the Eclectus parrot’s unique traits. Dr. Heinsohn employed a spectroradiometer to conduct objective optical measurements of the birds and their environment, accounting for the fact that parrots can perceive ultraviolet light invisible to humans. This instrument revealed how plumage colors might appear to parrots and their predators.
Optical measurements indicated that the male Eclectus’ green plumage provides excellent camouflage against the leafy treetops where they forage, making them inconspicuous to predators. Males spend considerable time foraging to feed themselves, a female, and possibly fledged young. Females, conversely, have less need for camouflage as they primarily stay near the nest hole, which offers a refuge from predators. Their coloration also serves a crucial function: females need to be conspicuous to compete for nest sites with other Eclectus and Sulphur-crested Cockatoos, who frequently occupy Eclectus nests. By calling and displaying outside their nests, females signal that the nest is occupied, thereby deterring potential intruders and minimizing conflicts, although fights, sometimes fatal, can still occur. [cite:4, cite:5]
Spectroradiometer data also uncovered that while males are camouflaged against foliage, their feathers reflect ultraviolet light visible to other parrots but not to humans or many predators. This means Eclectus parrots appear even more brilliant to each other than they do to humans.
Bizarre Breeding Behavior
The distinct parental roles of male and female Eclectus parrots are intrinsically linked to their differing coloration. Males, primarily responsible for foraging, require camouflage amidst leaves to evade predators, while females, tasked with guarding the nest, benefit from conspicuousness to ward off rivals and protect their young. Beyond coloration, Eclectus parrots exhibit a breeding system highly unusual for parrots. While most parrot species are monogamous, Eclectus parrots practice polygynandry, where both males and females may have multiple mates. A single female Eclectus can be courted and fed by up to seven males, and males, in turn, may court and feed more than one female.
This polyandrous behavior differs significantly from other bird species where females mate with multiple males. In species like phalaropes and sandpipers, males typically care for the young while the female seeks additional mates, and often, the female is the more brightly colored sex, reversing typical sex roles. Eclectus females, however, actively guard the nest and young while receiving sustenance from multiple males. They then feed the nestlings, and the males feed the young after fledging. Unlike females in many other polyandrous species, Eclectus females do not abandon their eggs after laying.
The ability of a female Eclectus to remain at the nest is facilitated by one or more males providing her with food. The motivation for multiple males to attend a single female, however, remained a question. In many animal species, males unable to secure a mate may remain solitary. Alternatively, young males and females who fail to find mates may assist their relatives, typically their parents, in raising offspring. This concept, known as “kin selection,” proposed by evolutionary biologist Bill Hamilton, suggests that animals can propagate their genes by helping close relatives reproduce. Such helping behavior, often observed in species like Florida Scrub Jays and African Bee Eaters, provides benefits such as increased reproductive success for the family unit and valuable experience for the helpers.
To test the hypothesis that male Eclectus parrots assist their mothers in raising more young, Dr. Heinsohn’s team collected DNA from females, their chicks, and their suitors. Their findings revealed that male Eclectus are generally not closely related to the females they court, indicating that kin selection does not explain the phenomenon of multiple males attending a single female.
Dr. Heinsohn ultimately discovered that this unusual breeding behavior stems from a male-biased sex ratio combined with a scarcity of suitable nest holes. Female Eclectus experience higher mortality rates than males, resulting in a larger male population. Furthermore, suitable nesting sites are limited. Eclectus require specific nesting holes that do not flood during rainstorms or dry quickly, as their chicks are vulnerable to drowning. The preference for nesting holes with sideways entrances further restricts availability. This shortage of quality nest holes means that not every male can secure a mate with a nest, leading to each female attracting multiple partners.
Consequently, a male Eclectus has a significant chance of contributing to the rearing of young he did not sire. To maximize his reproductive opportunities, a male must court a female, even when she is already being courted by others. Over time, his chances of fathering offspring increase, though success varies greatly among individuals. Some males attempt to increase their chances by mating with multiple females, with one documented instance of a male fathering young with two females located 7.5 km apart.
Another Mystery Unveiled
Beyond their distinct sexual dimorphism and peculiar breeding habits, Eclectus parrots exhibit another puzzling trait: some females produce a preponderance of offspring of one sex before switching to the other. Despite these individual biases, the overall fledgling sex ratio in a population typically hovers around 50:50. The reason behind these runs of a single sex remains unclear. However, Dr. Heinsohn proposes a hypothesis, to be tested, suggesting that females with higher-quality nest holes and abundant male attention are more likely to produce males. Given that male chicks are larger and require more food, females may favor raising them only when ample resources are available. A similar strategy is employed by the critically endangered Kakapo parrot of New Zealand, where supplementary feeding enables females to produce more male chicks, which are larger and more resource-intensive than females.
Conclusion
Through extensive research, biologists have begun to unravel the mysteries surrounding the Eclectus parrot’s extraordinary coloration and unusual breeding system. Dr. Heinsohn’s decade-long work has provided significant insights into these aspects. He is now turning his focus to the magnificent Black Palm Cockatoo, another parrot species known for its unique drumming displays. His team is developing methods to identify individual cockatoos by their vocalizations and investigate the species’ notably low reproductive rate.
Acknowledgements
The author expresses gratitude to Dr. Rob Heinsohn for his invaluable contributions, information, and insights regarding his research on Eclectus parrots.
References
- Marshall, R, and Ward. I. 2004. A Guide to Eclectus Parrots as Pet and Aviary Birds, (revised edition). ABK Publications. South Tweed Heads, NSW, Australia.
- Grafen, A. 2000. Biologist who died after Congo expedition was leading Darwinian theorist who explained how natural selection acts on social behaviour. The Guardian. March 9.
- Heinsohn, R., Murphy, S., and Legge, S. 2003. Overlap and competition for nest holes among eclectus parrots, palm cockatoos and sulphur-crested cockatoos. Australian Journal of Zoology, 51, 81-94.
- Legge, S., Heinsohn R., and Garnett, S. 2004. Availability of nest hollows and breeding population size of eclectus parrots, Eclectus roratus, on Cape York Peninsula, Australia. Wildlife Research, 31, 149-161.
- Heinsohn R., Legge S., and Endler J.A. 2005. Extreme reversed sexual dichromatism in a bird without sex role reversal. Science, 309, 617–619.
- Heinsohn R, and Legge, S. 2003. Breeding biology of the reverse-dichromatic, co-operative parrot, Eclectus roratus. Journal of the Zoological Society of London, 259,197-208.
- Heinsohn R., Ebert, D., Legge, S., and Peakall R. 2007. Genetic evidence for cooperative polyandry in reverse dichromatic Eclectus parrots. Animal Behaviour, 74, 1047-1054.
- Heinsohn R. 2008. The ecological basis of unusual sex roles in reverse-dichromatic eclectus parrots. Animal Behaviour, 76, 97-103.
- Heinsohn, R., Legge, S., and Barry, S. 1997. Extreme bias in sex allocation in Eclectus parrots. Proceedings of the Royal Society of London Series B – Biological Sciences, 264, 1325-1329.
- Clout, M., Elliott, G., and Robertson, B. 2002. Effects of supplementary feeding on the offspring sex ratio of kakapo: a dilemma for the conservation of a polygynous parrot. Biological Conservation, 107, 13-18.
Sidebar: Why are many male birds so extravagant?
In sexually dimorphic bird species, males often display more extravagant appearances than females, who tend to be duller. This is generally attributed to female preference for flashy, brightly-colored males, as vibrant plumage can signal good health and foraging ability. Studies have also indicated that brightly-colored males may exhibit greater resistance to parasites. Such gaudy feathers can act as a “handicap,” demonstrating a male’s superior predator-evasion skills to survive despite being conspicuous. By mating with a showy male, females increase the likelihood that their chicks will inherit advantageous traits such as strong foraging capabilities, parasite resistance, or enhanced predator-evasion skills. Female birds typically exhibit greater choosiness in mate selection because they invest more energy into reproduction, primarily through the production of large eggs. Consequently, mating with an unsuitable male can incur a higher cost for a female compared to a male who chooses a poor mate.
