This instrument measures various properties of the light reflected or emitted off of objects. It was important to make objective measurements using such an instrument, because parrots do not see the world the way humans do. Parrots can see light into the ultraviolet spectrum, which is invisible to people. This means that an object which blends in with its environment to a person may actually be very conspicuous to a parrot.

The optical measurements indicated that male Eclectus, with their largely green plumage, blend in well with the leafy treetops amongst which they forage. This makes them inconspicuous to the raptors that prey on them.⁵ Males spend several hours each day foraging because they need to feed not only themselves, but a female or two, and possibly some newly fledged young.⁶ Females do not have as large a need to be camouflaged, since they spend most of their time in or near a nest hole in which they can hide should a predator show up.

Additionally, the females actually do need to be quite conspicuous at times. They must compete for nests with other Eclectus and with Sulphur-crested Cockatoos, who often take over Eclectus nests.³ Female Eclectus will display outside their nests by calling and drawing attention to themselves,6 and their colour makes them stand out very well against a leafy canopy.⁵

By being very conspicuous, a female can let other parrots know that her nest hole is taken and that they should stay back. This often works to prevent conflicts, but even so, females still sometimes have to fight off intruders, primarily other parrots. Fights between Eclectus can be very intense, and even fatal.⁵

The spectroradiometer measurements revealed another aspect of Eclectus biology that would have remained a secret had not such an instrument been used. While male Eclectus are difficult for predators to see against green leaves, they are quite conspicuous when seen by other parrots outside of a nest hollow.⁵ Green does show up well against a brown tree trunk, but the measurements from the spectroradiometer showed that an Eclectus’ feathers also reflect ultraviolet light that other parrots can see, but that humans and many of the Eclectus’ predators cannot.⁵ So, while Eclectus look brilliant to people, they look even more brilliant to each other.

Bizarre Breeding Behaviour The coloration of the Eclectus, however, isn’t the only unusual characteristic of this extraordinary parrot that has baffled biologists. Their breeding behavior is also very strange for a parrot.  While most parrots are monogamous, Eclectus Parrots are polygynandrous, which means that both males and females may have multiple mates.  A female Eclectus may be courted and fed by up to seven males at once.⁷ The males are not monogamous either, and will sometimes court and feed more than one female.⁷ There are other bird species where females will mate with more than one male, although the behaviour of Eclectus is very different from the behaviour of these other polyandrous birds.  In most polyandrous birds (such as phalaropes and sandpipers), the male will care for the young while the female goes off and finds another mate.  In such species, it is often the female that is the more colorful sex, so the sex roles are essentially reversed. However, this is not so in the Eclectus, because the female will guard the nest hole and her young while multiple males will feed her.  She will then feed any nestlings present, and he will feed the young once they have fledged.  The female does not abandon the eggs after they are laid as do the females of many other polyandrous bird species. Why, though, will multiple males often tend to a single female?  In many animal species, if a male cannot find a mate, he may simply go without one and live as a bachelor.  In other birds, young males and females who cannot find a mate may stay around and help their relatives – usually their parents – raise young.  This is because natural selection shapes animals to act in ways that help them pass their genes on to a new generation. Of course, an animal can do this by bearing young, and its genes will be passed along through them.  However, an animal can also propagate its genes by helping its parents raise more of its siblings.  This is because identical copies of half of any animals’ genes are also present in their siblings because they share the same parents.  The theory that animals can pass their genes on by helping close relatives produce more young is called “kin selection,” and this idea was developed, in part, by the aforementioned Bill Hamilton.

Why are many male birds so extravagant? In sexually dimorphic bird species, males are usually very showy in appearance, while the females are very dull. This is because female birds often prefer to mate with flashy, brightly-coloured males, since male birds must be healthy and good at foraging to maintain colorful, vibrant feathers.  Additionally, in some species, biologists have shown that brightly-colored males are more resistant to parasites than duller males.  Bright colors or gaudy feathers also act as a “handicap” to the males that sport them, and any male bird that survives, despite being very conspicuous, must have excellent predator-evasion skills. If a female bird mates with a beautiful, showy male, her chicks could inherit his good foraging ability, his ability to resist heavy parasite infestations, or his superior predator-evasion skills.  The females of sexually dimorphic species are usually choosier than males because females put more energy into reproduction than males, since they need to produce large eggs. A female who mates with a “dud” may incur a bigger cost than a male who chooses a poor mate.

The presence of these helpers often increases the number of young a pair can raise, and the helpers also benefit by gaining valuable experience in caring for young.  Such helping behaviour has been well-studied in Florida Scrub Jays and African Bee Eaters.  It’s possible that Dr Hamilton’s insight on helping behaviour in animals may explain some of the Eclectus’ breeding behaviour.

One way to test the hypothesis that male Eclectus are helping their mothers raise more young would be to collect DNA from a female Eclectus, her chicks and her suitors, and see if they are closely related.  Dr Heinsohn and his team did exactly this and it turns out that male Eclectus are generally not closely related to the females they court.⁷  So, kin selection does not explain why more than one male may court and feed a single female.  There must be another reason for this odd behaviour.

In the end, what Dr Heinsohn did discover is that the Eclectus’ unusual breeding behaviour is the result of a sex ratio that is biased towards males, along with a shortage of suitable nest holes.⁷  Young females have a higher mortality rate than males, so there are simply more males out there than females.

There are also females that may not be able to breed because they cannot find good nest holes.  Good nest holes are rare, because it is not simply enough for an Eclectus to find a tree with a hole in it.  It must be one that either does not flood during rainstorms or one that dries out quickly, because Eclectus chicks can easily drown if their nest hole becomes flooded.⁸  Eclectus usually nest in holes that have entrances that face sideways, rather than straight up.  The lack of quality nesting holes means that there cannot be enough females with nest holes for every male, so each female ends up with more than one partner.