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

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Eye Spy; what colour is a bird's eye?

The simple answer is just about any colour at all; the tricky follow-up though is a two-parter, 'why and how?'. However if you're looking for answers to these questions, you probably don't need to read any further here - mostly we still don't know. For much of what follows I've drawn on a recent (2022) review paper by a team from Louisiana State University led by PhD student Eamon Corbett. This is a free 'preprint' article; the final published article (2023) is available here, but it is not free. 

I think it is very telling that, as of October 2023, only 2% of bird species and 21% of families have been studied in any way to determine what causes their eyes to be the colour they are. As with feathers, the colour of eyes (by which I mean irises) is determined by pigments, or physical structures, or a combination of both, though any given colour may be achieved in different ways in different species. I'll explain what we do know about the basis of various iris colours as we go, but mostly this is going to be  a celebration of the rainbow of colours in which bird eyes may parade. (Not quite a rainbow actually - there are very few green bird eyes that I know of, and I have no examples of them.)

In this post I have primarily used Australian examples, though have included some others where appropriate. Firstly the great majority of eyes are black or dark brown - in fact the proportion of 'dark' eyes is higher in birds than in other vertebrate groups that have been studied.

Barn Owl Tyto alba, Alice Springs Desert Park. It seems that melanins are responsible
for most of the dark eyes, but not all are in the same layers of the eye - not detail
we need to go into here! (Corbett goes into all of this in much more depth,
via the first link in the first paragraph of this post.)

Double-eyed Fig Parrot Cyclopsitta diophthalma, Cairns.
This may be an example of a phenomenon we'll delve into a little more below,
of a dark eye forming a highlight by contrasting with a bright background; the
reverse can also be found in other species.

Yellow-tailed Black-Cockatoo Zanda funerea in our backyard in Canberra.

Perhaps that's enough of black eyes; dark brown ones are probably formed similarly, by layers of melanins. 

Swift Parrot Lathamus discolor, Canberra. A rare bird, seriously endangered by habitat loss,
whose eyes we probably pay much less attention to than to the spectacular plumage.

Brown Quail Synoicus ypsilophorus, Bundjalung NP, north coast NSW.

This quail's eyes are probably reddish-brown, and this colour is fairly common too. (You'll probably be able to see these better by clicking on the photos.)

Brown Tinamous Crypturellus obsoletus, near Sao Paulo Brazil.
(I am determined not to get sidetracked today with interesting stories about
the birds or the locations!)

Noisy Friarbird Philemon corniculatus, Pilliga Forest, northern NSW.
This is a familiar big migratory honeyeater from eastern Australia.

Rainbow Bee-eater Merops ornatus, Longreach Waterhole, Northern Territory.

I'm no artist, or any other sort of expert on colour, but a fairly unusual extension of brown in eyes is hazel, usually described as 'brown-green'; I'm not sure about these, but I'm going to tentatively call them hazel. Always happy to be challenged of course, though I hope we can agree that they are very attractive eyes indeed!

Kori Bustard Ardeotis kori, Ngorogoro Crater Tanzania.

White-fronted Chat Epthianura albifrons, Canberra.
Australian chats are now known to be a group of honeyeaters.

It's of course impossible to determine when 'red-brown' becomes 'red' (not least because it's in the eye of the beholder as much as that of the bird), but here are some pretty impressive red eyes. It used to be assumed that the carotenoid pigments that cause feathers to be red, orange or yellow have the same effect in eyes, but as often is the case, while there are certainly carotenoids in some or even many eyes, it's not that simple. In addition to another class of pigments, pteridines and purines, blood vessels near the surface do the trick in quite a few birds and cholesterol crystals have an effect in some others. I've mentioned already how few species have been studied in detail, but inevitably most of those that have been are from the Northern Hemisphere. However here are a couple of red-eyed Australian birds whose eye secrets have been revealed to make the point that we just can't make assumptions here.

Black Swan Cygnus atratus Canberra. Its red eyes are due to an interaction of
melanins, cholesterol crystals and blood vessels.

Zebra Finches Taeniopygia castanotis, Great Sandy Desert, Western Australia.
Their red eyes are down to pteridine pigments.

As for the red eyes that follow, we can only assume that some of them are due to some combination of the above effects, and some are not! The swan's eyes are emphasised by being on a black background, and here are a few more (though by no means all I could have used) using this strategy. The whole body may be black, like the swan's...

White-winged Choughs Corcorax melanorhamphos, Canberra. I can be pretty
confident that blood vessels play a role here, as choughs can make their eyes
bulge and almost glow when they're threatening or being threatened.

Eurasian Coot Fulica atra and chicks, Canberra.

Metallic Starling Aplonis metallica, Cairns, north Queensland.

Pacific Koel Eudynamys orientalis, south coast NSW.

Spangled Drongo Dicrurus bracteatus, Canberra. This tropical and subtropical bird only
rarely comes as far south as Canberra, but this one hung around just around the
corner from us for a few days back in 2012.

...others have just a black head or even just a mask.

Black-fronted Dotterel Charadrius melanops, Cobar, western NSW.

Eastern Spinebill Acanthorhynchus tenuirostris, Blue Mountains, NSW.

Hooded Dotterel Charadrius cucullatus, Dhilba Guuranda–Innes NP, South Australia.

Chestnut Teals Anas castanea, south coast NSW. In this case only the males have the advantage
of the black contrast, though the females have the red eye too.

For many other species, like the female teals, the red eye alone is enough it seems, though in all these cases it is framed in a paler plain background.

Red-collared Lorikeet Trichoglossus rubritorquis, Darwin.

Olive-backed Oriole Oriolus sagittatus, Nowra, NSW.

Grey-cowled Wood Rail Aramides cajaneus, northern Peru.
These eyes really almost do glow in the dim rainforest understorey.

Fire-eyed Diucon Pyrope pyrope, Chilean Patagonia.
This tyrant flycatcher's eyes really are its outstanding feature.

Crested Duck Lophonetta specularioides, Chilean Patagonia.

And red grades to orange. This is probably often due to the influence of yellow carotenoids on some of the features that produce red, but remember the earlier comments on how much we don't yet know.

Crested Pigeon Ochyphaps lophota, Wagga Wagga NSW.

Dusky-legged Guan Penelope obscura, Peruibe, southern Brazil.

Hildebrandt's Starling Lamprotornis hildebrandti, Ngorogoro Crater, Tanzania.

Many birds have striking yellow eyes; in those few that have been studied contributing factors include pigments such as melanins, carotenoids, pteridines and purines, collagen fibres and oil droplets, in varying combinations. Take your pick regarding the following, all of which are in different Orders.

Australasian Shoveller Spatula rhynchotis, Canberra.

Pearl-spotted Owlet Glaucidium perlatum, Tangarire NP, Tanzania.

Grey Currawong Strepera versicolor, Gluepot Reserve, South Australia.
(This is the confusingly black mallee subspecies.)

Dolphin Gull Leucophaeus scoresbii, Ushaia, Argentinian Tierra del Fuego.

Collared Sparrowhawk Accipiter cirrocephalus (with House Sparrow lunch)
in our Canberra back yard.

Australasian Grebe Tachybaptus novaehollandiae, Canberra.

Before we get to white eyes, there are some I can only describe as 'pale', almost white but tinged with yellow or grey.

Yellow-billed Spoonbills Platalea flavipes, Canberra.

Osprey Pandion haliaetus, Hervey Bay, Queensland.

Bar-shouldered Dove Geopelia humeralis, Darwin.

Male Magpie-lark Grallina cyanoleuca, Canberra.

Which brings us to those birds, and there are quite a few, with striking white irises. These eyes may actually have various pigments, but in combination with colourless light-reflecting structures or chemicals these may produce white irises. And no, I'm afraid I don't really understand that either! Here are some, nonetheless, which I find particularly impressive.

Blue and Yellow Macaw Ara ararauna, Pantanal, south-west Brazil.

Grey-crowned Babbler Pomatostomus temporalis, Alice Springs, central Australia.

Hardhead (also known, much more helpfully, as White-eyed Duck) Aythya australis, Canberra.

New Holland Honeyeater Phylidonyris novaehollandiae, south-west Western Australia.

Pacific Gull Larus pacificus, Binalong Bay, Tasmania.

Radjah Shelduck Radjah radjah, Darwin. I'm not sure why this 'white on white'
works so well, at least for me, but I find it compelling.

Blue bird irises are not common, but when they are encountered they are most striking. As usual the mechanism has not been looked at very much, but it is assumed that the principle (as with most blue feathers) is the Tyndall Scattering Effect, where minute particles in a medium reflect light of a wavelength we see as blue. No pigments are involved, and indeed blue pigments are almost unknown in birds.

Chestnut-headed Oropendola Psarocolius wagleri, Costa Rica central ranges.

Galápagos Cormorant Nannopterum harrisi, Isla Fernandina.
This is the world's only flightless cormorant.

Little Black Cormorant Phalacrocorax sulcirostris, Canberra.

Spiny-cheeked Honeyeater Acanthagenys rufogularis, Cocoparra NP, NSW.

It is not such a big step from this to mauve, which is even rarer in birds' eyes.

Male Satin Bowerbird Ptilonorhynchus violaceus, National Botanic Gardens, Canberra.

Some birds also have, dare I say it, somewhat weird iris patterns; you'll need to click on these two pictures to enlarge to be able to see the effect..

I don't often feature this species, Australia's worst exotic bird pest, here, but Common Mynas
Acridotheres tristis, here in Sydney, have a most unusual iris comprising a ring of
white spots around the otherwise dark iris.

Golden-collared Toucanet Selenidera reinwardtii, Wild Sumaco Lodge, north-eastern Ecuador.
Toucanets in this genus have already striking green-yellow irises but with added large dark
patches on either side of the pupil.

In some species the irises change colour with age (as plumage commonly does) or are determined by sex.

Channel-billed Cuckoo Scythrops novaehollandiae, above and below, the world's largest cuckoo.
The adult above at Karumba, tropical Queensland, has startlingly red eyes (and eye ring).

This juvenile at Wollongong, south of Sydney, has brown irises which later turn red.

Likewise Silver Gulls Chroicocephalus novaehollandiae (the abundant and ubiquitous
Australian gull) has pure white irises as an adult - most of which have both feet by the way -
but they are dark in immature birds (below).

The sexes of Black-necked Storks Ephippiorhynchus asiaticus, here at Karumba
on the Gulf of Carpentaria in Queensland, differ in eye colour.
The female on the left has staring yellow eyes, while the male's are brown.

The story is the same with Galahs Eolophus roseicapilla, except that the female has
red eyes (here on the right) and the male's are again brown.

Earlier, while discussing red irises, I showed some examples of contrast with the surrounding feather colour, especially black plumage. Here are some more examples of eye colours accentuated by their surrounds, with black beings a 'popular' background. And I realise that I've feature a couple more red ones here - oh well, they're worth admiring!

Blue Dacnis Dacnis cayana, Peruibe, south coast Brazil.

Magpie Tanager Cissopis leverianus, Trilha dos Tucanos near Sao Paulo, Brazil.

Masked Flowerpiercer Diglossa cyanea, Yanacocha near Quito, Eucador.

Plush-crested Jay Cyanocorax chrysops, Pantanal, south-west Brazil.
(And apologies for the unfortunate background!)

Torresian Crow Corvus orru, central Australia.

And this one is in direct and, I find, pleasing contrast with the crow's white-on-black pattern.

White Terns Gygis alba, Lord Howe Island.
Here the black eye is showcased by the startlingly white plumage.

Finally - which may come as some relief to you - an entirely different kind of contrast which I'm pretty sure isn't just random. There are two species of oxpeckers, a genus of starlings, which make a living in sub-Saharan Africa picking ticks from the skin of large grazing mammals.The Yellow-billed Oxpecker Buphagus africanus is found right across the continent, while the Red-billed B. erythrorynchus is found only in the east. In each case the eye colour forms a strong yellow-red contrast with the bill, which I find fascinating.

Two oxpecker species on a giraffe in Serengeti NP in Tanzania.
The Red-billed has glaring yellow eyes, and the Yellow-billed (which actually has a red
tip to its bill) has bright red irises.

I had intended to finish with another way of drawing attention to eyes, that is with bare coloured skin surrounding them, but I think this is long enough already, and I'll leave that for another day. 

As for why all these different iris colours and patterns have evolved, I think that such evidence as there is (again thanks to Corbett's exhaustive review) points to the primary function as being in signalling to others of the same species, including offering information as to sex, fitness, ages etc. I'm content to leave it at that until there is further information available.

I hope you've been as interested in this topic as I've found myself being. If not at least I hope you've enjoyed gazing into a lot of very attractive eyes! Either way, thanks for reading this far.

NEXT POSTING THURSDAY 29 FEBRUARY

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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