About Me

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Canberra-based naturalist, conservationist, educator since 1980. I’m passionate about the natural world (especially the southern hemisphere), and trying to understand it and to share such understandings. To that aim I’ve written several books (most recently 'Birds in Their Habitats' and 'Australian Bird Names; origins and meanings'), run tours all over Australia, and for the last decade to South America, done a lot of ABC radio work, chaired a government environmental advisory committee and taught many adult education classes – and of course presented this blog, since 2012. I am the recipient of the Australian Natural History Medallion, the Australian Plants Award and most recently a Medal of the Order of Australia for ‘services to conservation and the environment’. I live happily in suburban Duffy with my partner Louise surrounded by a dense native garden and lots of birds.

Thursday 21 March 2024

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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Thursday 29 February 2024

Ubirr and Bardedjilidji; a special Kakadu corner

It's quite a while (too long in fact) since I've visited Kakadu National Park, a park of world significance, as evidenced by its UNESCO World Heritage Site listing. Covering two million hectares it is Australia's largest national park and one of the largest tropical national parks in the world. It is one of only four Australian World Heritage Sites to be listed for both its cultural and natural values. It has been inhabited for around 50,000 years, the last 40,000 of them at least being a continual occupation. Nearly 25% of Australia's native mammal species are found here, and almost 35% of its bird species - I could go on, but even if you're not already familiar with all this, there is plenty of information readily available on line, including its UNESCO listing which you can find here

Kakadu is at the end of the red arrow in the Top End of Australia (very terse and literal),
east of Darwin, the capital of the Northern Territory.

I have reported previously on other aspects of the park eg here for a perspective of visiting in the wet season; at the end of that post you can find a link to a further posting on a more conventional visit in the dry. Today however I want to take you to a small corner of the park, in the far north-east, dominated by Ubirr, a mighty sandstone outcrop looking out over the vast Alligator River flood plain to the west, and the East Alligator River to the east. This will be a relatively brief post, but I think it's a part of the park - and the country - that's worth sharing.

By clicking on the image you'll be able to see Ubirr in the far north-east.
Map courtesy of Parks Australia.


The Bininj/Mungguy people (Bininj in the north, Mungguy to the south) are intrinsically involved with the management of the park, as of course they have been for millennia. I'm not going to say a lot about them, through respect. This isn't as contradictory as it might sound; their stories are not mine to tell. I couldn't interpret their culture or perspectives even if I was impolite enough to try. There is good information available, including through the Parks Australia Kakadu website. If you can do a ranger-guided walk (including at Ubirr), it is highly recommended.

To get to Ubirr, turn north off the Arnhem Highway - Oenpelli Road just before it crosses the East Alligator River at Cahill's Crossing; it is well-marked and you'll have a map anyway. The circuit walk past the spectacular rock art (an important factor in the World Heritage Listing) is only a kilometre and mostly pretty benign, though for full benefit you'll do a bit of an extra climb up to the sublime lookout over the floodplain. 

Looking down onto the Alligator River flood plain, above and below. The South Alligator River
flows into the Timor Sea (as does the nearby East Alligator) some 60km to the west.
We were there in September towards the end of the Dry; there wasn't much water
evident on the plain, but it was still very green.

 
This is the view back to the east, and the East Alligator River in the near distance.

Kakadu is a vast sandstone landscape, and Ubirr is a superb example of it. The Arnhem Land Plateau is dominated by the Kombolgie Sandstone Formation, laid down by countless floods along great rivers originating somewhere to the north-west. The sands consolidated into sandstone about a billion years ago.

Looking across the sandstone of the top of Ubirr.
A more tumbled and uplifted area of layered sandstone.

Overhanging sandstone cliff faces - like those which form the nearby galleries -
along the walk to Ubirr.

A fig growing on the cliff face. There are a couple of species present, and I can't say which this is.
In other places Pandanus (Pandanus spiralis) is common both as understorey and as tall trees.

Pandanus growing as an understorey above...
.... with a tall tree towering above other smaller Pandanus plants.
Which brings us to the gallery.

The main gallery is on the face of the outcrops in the foreground below us.
 Most of the paintings date from the late 1500 years, and many of them feature animals which were (and are) important food items, many of them fish.

Stingray (and human shape to the upper left).
Fish of course - Barramundi perhaps?
(I'm not very good at fish, especially in the Top End!)

I'm pretty sure this is a different fish though.

In places the images are superimposed; to the top left is perhaps a sawfish?
 
Here a fish is joined by a turtle.
And another turtle.

Above the stingray that I featured above, is a bird - perhaps an Orange-footed Scrubfowl,
or maybe a Magpie Goose.
 And kangaroos are only to be expected!

These could represent any of several species found locally, including the shy and
not often seen (in fact never in my case!) Black Wallaroo.
And finally an interesting historical sketch, reporting on the appearance of a whitefella in the area. It is suggested that he could have an early buffalo hunter from the 1880s.
He seems to have his hands in his pockets and to be wearing heavy boots.
A painting which I particularly wanted to see, but didn't, clearly features a Thylacine. This magnificent marsupial predator vanished from the mainland about 3,500 years ago, coinciding with the arrival of the Dingo. (They continued to thrive in Tasmania, where Dingoes didn't appear, until the 1930s when systematic hunting tragically drove them to extinction.)
Photo courtesy Wikipedia.
South of the highway and just before the Ubirr turnoff, is the access to the lovely Bardedjilidji sandstone walk, a 2.5km easy stroll among mighty sandstone pillars and through Pandanus and eucalypt woodland.

Dramatic columns such as this one are features.
Strongly layered sandstone in a grassy woodland.
Caves and overhangs such as this provide cool shelters from the sun, with fig roots
providing extra hiding places for small animals.
We were there during a warm day, so didn't see as much wildlife as we would have if we'd been staying on site, but there were some nice birds to be seen.

Chestnut-quilled Rock Pigeon Petrophassa rufipennis. This is very much an Arnhem Land
sandstone special, being found nowhere else. Its only close relation is the very similar
White-quilled Rock Pigeon from further west in the Kimberley area.
Red-tailed Black-Cockatoo Calyptorhynchus banksii, a common but always thrilling
big resident of the tropical woodlands.
And yes, it does have a truly impressive red tail when it deigns to show it!

Rose-crowned Fruit-Dove Ptilinopus regina, truly a lovely bird, here checking
to see if the figs were suitably ripe. It is found widely in monsoon forests across
northern Australia and in east coast rainforests, but more usually is hidden
in foliage high above the ground.

Finally, adjacent to all this is the East Alligator River, and the highway crosses it at the infamous Cahills Crossing. It is famous for the number of Estuarine Crocodiles which gather around here at the end of the Dry (ie when we were there) to feed on fish, especially Barramundi, which are pushed by the high tide into shallow water at the crossing. However it is infamous for breathtakingly foolish visitors who approach to the edge of the water and even enter it to compete with the crocs for the Barramundi. It is tempting to think of this as a classic case of Darwinian selection in action, especially as there are nice safe and effective viewing platforms provided.
We were there at low tide, so didn't get to enjoy the main crocodile spectacle.
However we didn't miss out entirely, and I'm sure the Striated Heron
actually knew what it was doing.
Next time you go to Kakadu, don't miss out on Ubirr - it is a very special corner of a very special park.
Thanks for reading.
NEXT POSTING THURSDAY 21 MARCH
I love to receive your comments and in future will be notifying you personally by email when a new posting appears, if you'd like me to. All current subscribers have been added to this mailing list and have already been contacted. This will mean one email every three weeks at the current rate of posting. I promise never to use the list for any other purpose and will never share it.
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