Iridescence: living rainbows

A few years ago now, I talked about blue feathers (and other natural blues). The basis of blue in bird plumage has nothing to do with pigments, but everything to do with the physics of light. Very (perhaps too) simply, it involves structures, or layers of structures, in feathers or skin which reflect only wavelengths of light which we see as blue. If the structure of such a feather is damaged, it will usually appear a dull white. 

 

However there is another type of colouration which uses the same general principles. This is iridescence where a feather (for example) shines from one angle but not another, or gleams with one colour, then another with a shift of perspective. This is a crucial difference from the blue-feather light trick - the blue feather will always look blue from any angle, but iridescent ones can be dull black or the colour of the background feathers, or flash in a variety of coloured lights. Behind the precisely aligned layers of reflecting and refracting feathers is a simple layer of dark melanin; in fact you'll notice that quite a few of the examples that follow have their iridescence on a black feather base. Very nuanced aspects of the overlying layers can intensify or neutralise the iridescent impacts. An oil slick on water will produce the same effect, with light reflecting off both top and bottom layers which interfere with each other as the water ripples to create a rainbow effect - and 'iridescence' is from the Greek iris, a rainbow.

 

Here are some examples of the effect, via pairs of photos of the same bird taken only seconds apart..

Ruby-throated Hummingbird Archilochus colubris , Trilha dos Tucanos lodge, in the mountains
behind Sao Paulo, Brazil. It is as if the bird has suddenly flashed a light at us - or rather,
to the other Ruby-throats around. Hummers are highly possessive of a food source.

Pacific Black Duck Anas superciliosus, wing speculum. Many ducks have this patch of
iridescent feathers on the secondary feathers of the wing, here changing from blue-green
to purple in moments. This is the most familiar Australian duck,
which has adapted easily to urban park ponds.

Oasis Hummingbird Rhodopis vesper, Azapa, Atacama Desert, northern Chile.

Velvet-purple Coronet Boissonneaua jardini, Sachatamia Lodge, north-western Ecuador.
These photos show the iridescent more impressively than it probably looks - they
were taken on a sunless dull, rainy day which dulls the iridescent gleam.

A slight change of angle and the wing edges and thighs light up.

Purple-throated Mountaingem Lampornis calolaemus, Monteverde, central
Costa Rica cloud forest. Hummingbird names are really over the top,
but it's hard to be too cynical about them, especially when they suddenly look
like the next photo, again just seconds later.

And finally before we move on to individual examples of iridescent brilliance, here's a situation that I find especially dramatic. This time it's of two birds of the same species at different times, but the results from different lighting conditions is quite striking, and it's already one of the most striking birds in the world. This is the splendidly named Resplendent Quetzal Pharomachrus mocinno, a trogon from Central America and the national bird of Guatemala. These birds seen in the same light would look the same, but one is in shadow, the other in sunlight, and look at the difference!

Male Resplendent Quetzal in the dim light under the canopy in the cloud forest of the Savegre Valley
of the central ranges of Costa Rica. Each one we saw here looked the same, this rich gleaming blue;
we were astonished and initially perplexed after our previous experience with it.

Whereas this one nearby in the open (eating wild avocadoes) was brilliant green,
which is how the field guides portray them.

It is no coincidence that I chose four hummingbirds as illustrations of iridescence in action - they are probably the world leaders in bird iridescence, in terms of the number of species that flaunt it. I'm also hopelessly in love with them. However I'll now move on to some other bird families which also iridesce - it's a widespread phenomenon and the following representatives come from 20 quite different families. I hope that's not too much, but it's a really just a celebration of these birds and the fabulous forms that their iridescence can take. If you prefer you can just scroll through the pictures, read what you feel like, and hopefully feel as uplifted as I do while I'm selecting and sharing them. And on the off chance that you're not yet sated with hummers I'm going to offer some more just before concluding - and with great discipline and restraint I've limited myself to just eight!

 

The families are in random order, and I've chosen only one or two representatives.in most cases. Parrots don't feature heavily in this discussion, perhaps because most are already strikingly coloured and don't need extra bling. It's probably no coincidence that this one is very sombrely coloured and lives in a dully coloured environment.

 

Austral Parrot Enicognathus ferrugineus, Chilean Patagonia.
This the world's most southerly parrot, occurring down to Tierra del Fuego
on the very tip of South America. The iridescence on the head is
subtle, but doubtless shows better in sunlight.

Quite a few ducks, on the other hand (including the Pacific Black Duck shown above), are members of the iridescent club. Most use the black duck's wing speculum approach, but here's one that doesn't restrict itself to that.

Male wild Muscovy Duck Cairina moschata, Pantanal, south-western Brazil.

Sunbirds, as the Old World equivalent of hummingbirds (though not related) are unsurprisingly aficionados of iridescence, but I find I'm rubbish at getting decent photos of them. (I've tried to blame the birds but then heard mum's ghost muttering about 'poor workmen blaming tools', so I'll desist. It does make it a lot easier to make choices when most of the options are terrible!)

Beautiful Sunbird (and there's an unhelpful name!) Cinnyris pulchellus,
Serengeti NP, Tanzania.

Eastern Double-collared Sunbird Cinnyris mediocris Lake Nakuru NP, Kenya.

I wouldn't have thought of storks in this context, but a look at this pair's necks shows I'd have been wrong.

Pair of Black-necked Storks Ephippiorhynchus asiaticus, Norman River,
Gulf of Carpentaria, tropical Queensland.

Another group of large waders can be pretty flash at times too.

Hadeda Ibis Bostrychia hagedash, Uganda. This raucous ibis (from which it gets its name)
is common in sub-Saharan Africa, but its wing iridescence isn't often remarked upon.

Nor are Australian ibises lacking in this department.

The Glossy Ibis Plegadis falcinellus, here in Canberra where it's a rare visitor, is an obvious
candidate; it is widespread in Africa and Australia and scattered in Asia and the Americas.

However the Straw-necked Ibis Threskiornis spinicollis, abundant in Australia,
isn't so often cited as iridescent, though the whole wing can shine on occasions.

Likewise we don't often think of finches (ie family Fringillidae, rather than the grass finches of Africa, southern Asia and Australia) as iridescent either, but some of the Neotropical euphonias and chlorophonias certainly qualify.

Chestnut-bellied Euphonia Euphonia pectoralis, Trilha dos Tucanos lodge,
in the mountains behind Sao Paulo, Brazil

The starling family, on the other hand, is replete with iridescence; here are some representative species.

Superb Starling (sometimes dubbed 'superstar') Lamprotornis superbus, at the breakfast table,
Buffalo Springs Reserve, northern Kenya. That glowing necklace compensates for its cheek.

Rüppell's Starling Lamprotornis purpuroptera, Serengeti NP, Tanzania.

Metallic Starling Aplonis metallica, Cairns. Australia' only native starling, and
its ancestors only arrived recently. A shining (albeit rambunctious) beauty.

Quite a few swallows also catch the light beautifully.

Pacific Swallow Hirundo tahitica, Sabah, Malaysian Borneo.

Ethiopian Swallow Hirundo aethiopica, northern Cameroon.

Some cuckoos carry their iridescence in their names, but those are not the only ones to shine.

Shining Bronze-Cuckoo Chrysococcyx lucidus, Canberra.

Pacific Koel Eudynamys orientalis, Canberra (taken from my driveway in fact).
Sometimes we get so caught up in its insistent all-hours calling, or its
breeding habits (here it exclusively parasitises Red Wattlebird nests)
that I think we forget just how beautiful a bird it is.

The mostly Neotropical tanagers are among the most colourful groups of birds in the world, but some of them gild the lily with some iridescence thrown in as well.

Saffron-crowned Tanager Tangara xanthocephala near Machu Picchu, Peru.

 

Ruby-crowned Tanager Tachyphonus coronatus, inland of Sao Paulo, Brazil.
This beauty is restricted to the highly threatened Atlantic forests of eastern Brazil.

 

Masked Flowerpiercer Diglossa cyanea, Yanacocha Reserve
near Quito, Ecuador. Not all tanagers have 'tanager' in the name
(and some 'tanagers' are actually something else, but we won't go there!).
This group makes a living by punching a hole in the base of a flower and
'stealing' the nectar without pollinating.

From now until the big hummingbird finale, I'm only going to offer one glossy example per family; after the hummingbirds' return appearance I'll be ending with four Australians.

Yellow-fronted Woodpecker Melanerpes flavifrons, another from the wonderful
Trilha dos Tucanos lodge in the Atlantic forests near Sao Paulo. I've not noticed
iridescence in many woodpeckers, but this one qualifies.

Green Wood-hoopoe Phoeniculus purpureus, Lake Nakuru NP, Kenya.
This belongs to a small African family, not hoopoes though they are in the same suborder.

Here's another from the same Order, though a different Family again.

Oriental Pied Hornbill Anthracoceros albirostris, Sabah, Malaysian Borneo.
Another group that I don't normally associated with iridescence but
I find that the more I look the more I find!

I'd not have thought that kingfishers would generally need any help to look gorgeous,
but this tiny Malachite Kingfisher Corythornis cristatus at Lake Mburo NP, Uganda,
has beautiful glowing spots on head and wing edges.

Pitta-like Ground-roller Atelornis pittoides, Ranomafana NP, Madagascar.
Bad photo but a tricky bird and the best I could do - I'm privileged to have
even seen it. This small family is endemic to Madagascar.

As promised/threatened, here are some more iridescent hummingbirds (and you can't imagine how many I've left out!). I don't think they need much commentary from me.

Blue-mantled Thornbill Chalcostigma stanleyi, El Cajas NP, southern Ecuador,
at 4000 metres above sea level.

Fiery-throated Hummingbird Panterpe insignis, central ranges, Costa Rica.

Green-crowned Woodnymph Thalurania colombica, Tandayapa Valley, north of Quito, Ecuador.

Lesser Violetear Colibri cyanotus, Monteverde, Costa Rica.

Long-tailed Sylph Aglaiocercus kingii, on the eastern slope of the Andes in
northern Ecuador. There is a sister species on the western slopes.

    Purple-bibbed Whitetip Urosticte benjamini, Tandayapa Valley, north of Quito, Ecuador.

Stripe-tailed Hummingbird Eupherusa eximia, Monteverde, Costa Rica.

Violet-bellied Hummingbird Chlorestes julie, Umbrellabird Lodge, southern Ecuador.

I do hope that wasn't too tedious! :-) And finally, some Australians who iridesce.

Satin Bowerbird Ptilonorhynchus violaceus eating Lilly Pilly berries,
National Botanic Gardens, Canberra.

Shining Flycatcher male (she is chestnut and white) Myiagra alecto,
Kakadu NP, Northern Territory.

Spangled Drongo Dicrurus bracteatus, Canberra (just round the corner in fact);
this one of only two I've seen in Canberra in over 40 years, though they are
common further north.

Splendid Fairywren Malurus splendens, Gawler Ranges, South Australia.
Splendid as he is, he's not yet finished moulting into his full summer beauty.

And that's it for a somewhat extended investigation of iridescence in birds from around the world. It's worth keeping an eye open - there's more of it about than you might expect. Thanks for reading this far, it's been quite a journey.

NEXT POSTING THURSDAY 11 APRIL

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