Naturally Green

It's been a while now since I offered one of my intermittent series on colour in nature. The last two series were on yellow and blue. I mention these specifically because both are essential to understanding green in animals. Among vertebrates in particular, green pigments are almost unknown (like blue), and what looks green to our eyes is a clever sleight of hand (or eye), almost universally formed by a combination of yellow pigments (especially carotenoids which, as mentioned in the earlier article, must be obtained from plant material) and structural blue. In very brief, this involves light scattering by appropriately sized 'bubbles' in feathers or skin which reflect only blue light - there's a lot more detail in the earlier posting, linked above.

Musk Lorikeet Glossopsitta concinna, Coles Bay, Tasmania.
The lorikeets are little nomadic blossom specialists, all basically green.
(They are also shameless with regards to colour coordination!)

Like virtually all green birds, the lorikeets' feathers are really yellow, with blue light reflecting through them, which our eyes interpret as green. Presumably green confers camouflage protection in foliage - though in the case of the parrots, the contrasting other colours (mostly pigments) might seem to defeat that purpose! Here are some more examples - enjoy!

Mulga Parrot male Psephotus varius, inland Western Australia.
These stunning little parrots are found throughout much of the Australian inland -
not just in Mulga, woodlands dominated by Acacia aneura.

Yellow-crowned Parrots (or Amazons) Amazona ochrocephala and Mealy Parrots A. farinosa,
Blanquillo clay lick, Peru.

 

Spotted Catbird Ailuroedus melanotis, Atherton Tablelands, tropical Queensland.
An apparently 'primitive' bowerbird which  doesn't build display bowers.

Western Violaceous (White-tailed) Trogon Trogon chionurus, Cerro Blanco Reserve, Ecuador.
For non-Americans, trogons are one of the most delightful surprises in the neo-tropics.

Crimson-rumped Toucanet Aulacorhynchus haematopygus, Paz de las Aves, Ecuador.
An exquisite tiny toucan, sometimes seen at fruit feeders.

The principle applies not just to birds however. Frogs, despite famously being green (though most aren't!), have no green pigments either. Their skin structure is very complex; blue frogs have a layer of dark melanophores, overlaid by iridophores that reflect blue light. Green frogs have a layer of yellow pigmented xanthophores on top of that - extraordinary! But clearly to those frogs that possess it, green is an important colour to be.

Litoria moorei, Margaret River, south-west Western Australia.
This beauty is known as the Motor Bike Frog for its remarkable call.

unidentified tree frog, Bwindi Impenetrable National Park, Uganda.

I believe that green reptiles get their colour thus too, though I'm not sure that much work has been done here.

Amazonian Racerunner Ameiva ameiva, Manu National Park, Peru.
Widespread in the neotropics, and introduced into North America.

Green tree snake Thrasops batesii, Limbe Botanic Gardens, Cameroon.

Many green butterflies too rely on yellow pigments and reflected light to achieve the effect; the microstructure of butterfly and moth scales is extraordinary.

butterflies, Manu River, Peru.
Million of butterflies congregate on the river banks, where their coiled proboscises
are as useful for taking up water as nectar.

Splendid Ghost Moth Aenetus ligniveren, Namadgi National Park, above Canberra.
This moth astonishes me - both wings and fur are green, both achieved by bending light to suit its needs.

beetle, perhaps a cockchafer, subfamily Melolonthinae, on Acacia, Leeuwin Naturaliste NP,
south-western Western Australia.
I am confident that this too relies on light diffraction.

What I am uncertain of with regard to the beetle is whether pigment is also involved, or whether a different wave-length is being reflected, so that it is green, rather than blue light being bounced to our eyes. Certainly several bird groups use this more direct approach to produce green. Here are some examples.

Rainbow Bee-eater Merops ornatus, Fraser Island, Queensland.
Australia's only bee-eater, but a pretty nifty one!

Dollarbird Eurystomus orientalis, a roller, and also our only species; they are closely related to bee-eaters.

Rufous-tailed Hummingbird Amazilia tzacatl, Ecuador.

Broad-billed Motmot Electron platyrhynchum, southern Ecuador.
Motmots are also in the same order as bee-eaters and rollers, probably not a coincidence that they
share this green-producing mechanism.

Emerald Dove Chalcophaps indica, Lord Howe Island.
Many fruit doves share this characteristic too; this one is found from India to Australia.

A very few birds however do produce their own green pigments; best known are the wonderful African turacos, which manufacture turacoverdin, a copper-based porphyrin, from fruit. The turaco reds, turacins, are derived similarly; it has been calculated that the feathers of a red and green turaco contain some 20mg of copper, to derive which some 20kg of fruit must have been eaten, which would take two to three months! Clearly he is making a statement.

Touraco page from Birds of Western Africa, Borrow and Demey, Helm Guides.

It has recently been recognised that a few other birds - some jacanas and pheasants, and the Indonesian Crested Wood-partridge - also produce turacoverdins.

Another class of chemicals, biliverdins, are also utilised by some animals as green pigments - mostly these are invertebrates, but they are used in some fish bones that are green (!) and oddly, in emu and cassowary eggs!

Emu eggs, south-western Queensland.

Grasshoppers and mantids also employ biliverdins.

unidentified grasshoppers:
Currawinya NP, south-west Queensland (above),
and Mt Kupé, Cameroon (below).

Praying Mantis, subalpine Namadgi National Park, above Canberra.

And finally, for today at least, some of the many green caterpillars take their pigments from the degradation products of photosynthesis that they eat - a useful camouflage tool.

Hawkmoth (?) caterpillar, Uluru National Park, central Australia.

It may or may not be easy being green, but it's certainly a complex process becoming so!

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