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..
Oasis Hummingbird Rhodopis vesper, Azapa, Atacama Desert, northern Chile. |
A slight change of angle and the wing edges and thighs light up. |
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!
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.
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. |
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. |
Pacific Swallow Hirundo tahitica, Sabah, Malaysian Borneo. |
Ethiopian Swallow Hirundo aethiopica, northern Cameroon. |
Shining Bronze-Cuckoo Chrysococcyx lucidus, Canberra. |
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.
Ruby-crowned Tanager Tachyphonus coronatus, inland of Sao Paulo, Brazil. This beauty is restricted to the highly threatened Atlantic forests of eastern Brazil. |
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! |
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. |
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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2 comments:
Thank you Ian, for another riveting newsletter, with brilliant photos, the colours in those birds and butterflies are stunning.
Hi Anthony and thanks for this, appreciated. That poor sunbird is being badly disrespected there! I've not seen that one, but I have seen the gorgeous kingfisher in Borneo. However I was quite unable to get it to perch on my hand, so my photo isn't nearly as good. In the dim understorey light it doesn't look at all iridescent, thanks for that.
Hello Maureen and always good to hear from you. They really do brighten up a day, don't they?
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