Yellow, not so Mellow in Nature

[This is another in a sporadic series of postings on colour in nature; the most recent one is here, from where you can find links to older ones, or you can find them all by clicking on Colours in Nature under Labels on my blog home page.]

Yellow, like red, is mostly worn to be seen. "Here I am! Come and share my genes!" or maybe "Here I am! Come and feed with me, we'll be safer together", or even perhaps "Here I am! Take the hint and leave me alone, or it might be unpleasant for you."

Yellow Warbler (or Mangrove Warbler) Dendroica (or Setophaga) petechia - this is a bird who has an identity crisis, though it doesn't know it! - Puerto Ayora, Galapagos.

Like most birds, this glorious and friendly little warbler derives its rich yellows from carotenoids in its diet - fat-soluble plant pigments which may come from leaves, fruit or seeds, or from insects which have eaten carotenoid-bearing plants.The same plant carotenoids may be utilised in different ways by different birds, so may appear as reds or oranges also.

Many birds have opted for yellow plumage - though most have it as part of the overall ensemble, rather than the dominant theme like the Yellow Warbler.

New Holland Honeyeater Phylidonyris novaehollandiae on Calothamnus sp.,
Cape le Grande National Park, Western Australia. The yellow wings are particularly prominent
when this abundant honeyeater flies out of a feeding bush; perhaps warning others of potential danger?

Eastern Yellow Robin Eopsaltria australis, Monga National Park, New South Wales.

Cinnamon-chested Bee-eater Merops oreobates, Bwindi Impenetrable Park, Uganda.
Colour is in the eye of the beholder, and I reckon this lovely bird's chest is yellower than any cinnamon I've met.

Gilded Barbets Capito auratus, Sacha Lodge, Ecuador.
A bird of the rainforest canopy, where yellow may be a good marker for others of its kind to see it.

White-browed Robin-chat Cossypha heuglini, Entebbe, Uganda

Black-chinned Mountain Tanager Anisognathus notabilis, La Paz de las Antpittas, Ecuador.
This species and the next live in the gloomy understorey of the tropical forests; again yellow is a way to enable
mates to keep in touch.

Western Violaceous Trogon Trogon ramonianus, Cerro Blanco Reserve, Ecuador.

 

The distribution of carotenoids in a bird's body is not limited to feathers however. Bills, legs and bare skin may also be carotenoid-yellow.

Choco Toucan Ramphastos brevis, Rio Silanche Reserve, Ecuador.
Both feathers and bill contain yellow carotenoids.

Southern Yellow-billed Hornbill Tockus leucomelas, Etosha National Park, Namibia

In some species exaggerated exposed skin - particularly in the form of wattles - is used for display.

African Wattled Lapwing Vanellus senegallus Murchison Falls National Park, Uganda.
This species has opted for yellow bill, legs and wattles!

Uniquely among birds, apparently, parrots synthesise their own yellow pigment - psittacofulvin.

Yellow Rosella Platycercus elegans flaveolus, Berri, South Australia.
Formerly given full species status.

Superb Parrot Polytelis swainsonii, Canberra.
Superb Parrots spend a lot of time feeding on the ground in grass, where the yellow and red chin and cap stand out.

Very recently it has been recognised that Macaroni Eudyptes chrysolophus and King Penguins Aptenodytes patagonicus, with yellow crests and necks respectively, utilise a pigment never before seen in birds; to my knowledge it has still not been described. 

Other birds manufacture a different group of pigments again, the pterins, specifically to produce yellow eyes; these too seem not to have been widely studied.

Powerful Owl Ninox strenua, National Botanic Gardens Canberra.

Spendid Starling Lamprotornis splendidus, Entebbe Botanic Gardens, Uganda.

Other vertebrates do things differently again. Mammalian hair colour relies on melanins; pheomelanins produce red-yellowish colours, though rarely as bright a colour as some of the bird pigments produce.

Yellow-footed Rock-Wallaby Petrogale xanthopus, Flinders Ranges, South Australia

Sumatran Tiger Panthera tigris sumatrae, Adelaide Zoo.

In fish, frogs and reptiles, most yellow is produced by the presence of xanthopores within the skin, containing pigments, primarily pteridines, produced by the animals rather than acquired from plants.

Northern Corroboree Frog Pseudophryne pengilleyi, captive animal, Canberra.
One would suspect that this colour combination signals a poisonous defence.

Holy Cross Toad Notaden bennetti, Cunnamulla Queensland.
After rain thousands of these dramatic frogs emerge from burrows. There are no true toads native to Australia.

Yellow-spotted Goanna Varanus panoptes, Bladensburg National Park, Queensland

And that's quite long enough a posting for today, though it would have been easy to continue on. Instead I'll talk a bit about yellow invertebrates next time.

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