The fact that multiple males may mate with any one female means that, in any given season, there is a good chance that a given male Eclectus will be helping to raise young that he did not father.  However, a male Eclectus needs to court a female, even though she may be being actively courted by other males, if he is to have any offspring.  As time goes on, he will become more likely to actually father young.

This can take years, because some males are far more successful than others in fathering young.⁷  Some male Eclectus will also mate with more than one female to increase his chances of fathering young.  In one instance, a male had young with two females situated 7.5 km apart.⁷  He must have been an extremely busy bird!

One more mystery to solve
Aside from their unusual form of sexual dimorphism and bizarre breeding behaviour, Eclectus parrots have another odd trait that biologists struggle to explain.  Some females will produce many offspring of one sex before switching to producing chicks of another sex.⁹  However, the overall sex-ratio of fledgling Eclectus parrots in a population is usually close to 50:50.

Currently, no one knows for sure why some Eclectus produce runs of one sex of chicks.  However, one hypothesis that Dr Heinsohn plans to test is that the females produce more males when they have higher-quality nest holes and are being fed by many males.  Since male chicks in the wild are bigger and require more food, females may raise them only when they have access to plenty of food.  This strategy is used by Kakapo parrots, which are a critically endangered, flightless parrot from New Zealand.  When female Kakapo are given supplementary food by biologists, they are more likely to raise male chicks, which are bigger and require more food than females. (10)

Conclusion
Biologists now have an answer to one of ornithology’s biggest mysteries: how the Eclectus got its unusual colors.  We also now understand why they have such an unusual breeding system, thanks to the ten years of work done by Dr Heinsohn and his team.

He is currently working on demystifying the habits of another unusual parrot species: the magnificent Black Palm Cockatoo.  These cockatoos are well-known for the drumming display that males perform by their nest hollows.  They will take a large stick and bang it on the edge of the nest entrance, like they are playing a drum.  Dr Heinsohn and his team are working on developing methods to identify individual cockatoos by their voices and are interested in determining why this species has such a low reproductive rate, which is one of the lowest for all parrot species.

Acknowledgements
I want to thank Dr Rob Heinsohn for providing information about his work on Eclectus Parrots and for answering my questions about them.

References
1. 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.

2. 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.

3. 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.

4. 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.

5. Heinsohn R., Legge S., and Endler J.A. 2005. Extreme reversed sexual dichromatism in a bird without sex role reversal. Science, 309, 617-619.

6. 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.

7. 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.

8. Heinsohn R.  2008.  The ecological basis of unusual sex roles in reverse-dichromatic Eclectus Parrots.  Animal Behaviour, 76, 97-103.

9. 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.

10. 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.

Jessie Zgurski is a senior PhD student in ecology from Edmonton, Alberta, Canada, who studies the behaviour and evolution of pikas.  She also has an MSc in systematics and evolution from the University of Alberta and a BSc in biological sciences from the University of Lethbridge.  She is a regular contributor to Parrots magazine and shares her home with a Lesser Sulphur-crested Cockatoo, a Red-lored Amazon, a Maroon-bellied Conure, a Jenday Conure, two Budgerigars and two Lineolated Parakeets.  When not working on her thesis or writing about parrots, she enjoys traveling (especially to see wild parrots), birdwatching, hiking, and horseback riding.  She also has a blog devoted primarily to parrots at zoologica.wordpress.com.  She can be reached at jzgurski@ualberta.ca.