Chris Watson

Thorny Devil

Owlet-nightjar ant-eating behaviour

Birding, Tourism, ResearchChris Watson

Australian Owlet-nightjar Aegotheles cristatus, basking in daylight at a roost hollow. Front-facing eyes, super cryptic, super creepy and, apparently, prodigious ant-eaters.

Recently, I had an interesting encounter on a photographic tour I was leading in Central Australia.

I’ve read about the foraging tactics and diet of Australian Owlet-nightjar Aegotheles cristatus, before, most memorably in the work of Dr Lisa Doucette. An article Dr Doucette wrote in The Bird Observer back in Feb 2011, really stuck in my mind. In that piece, she detailed the differences in the dietary composition between birds studied in the semi-arid ranges of Central Australia and the wet eucalypt woodland of NSW’s Northern Tablelands.

The bit that really stuck with me was the following paragraph elaborating on the fact that the largest portion of the desert birds’ diet (31% by volume) comprised… ants.

“Catching ants, an abundant, reliable taxa, active even at sub-zero temperatures, would require less energy and time to obtain.

Flightless worker ants that primarily forage and nest on the ground were the dominant prey type in the Australian Owlet-nightjar’s diet overall. This strongly indicates that the Owlet-nightjars are foraging on the ground following trails of ants and exploiting nests, not simply using a “perch-and-pounce” approach to capture large terrestrial prey. Relative to other species of nightjar, owlet-nightjars have longer legs, making them far more agile on the ground and better enabling them to exploit terrestrial prey.” - Dr Lisa Doucette, Foraging tactics of the Australian Owlet-nightjar, THE BIRD OBSERVER, No. 868, Feb 2011, p.6-8.

This astonished me for two reasons primarily: I’d never thought of Owlet-nightjars as being even remotely long-legged and; ants seemed an unlikely prey item for an animal equipped with a beak that appears best adapted for catching airborne prey. (Now, looking at my photo of the beastie above, I should have been more observant - it clearly has a decent set of pins.)

It was illuminating.

I never thought I’d witness this curious behaviour, not least because even in Central Australia where the birds are incredibly common, despite hearing them on most nights out in the scrub, I didn’t see them very often at all. The mental image of an Owlet-nightjar perched on the ground over a line of ants like some weird gigantic feathered Thorny Devil was incongruous. But it happened.

The more-famous Central Australia ant-eater, the Thorny Devil, Moloch horridus.

Wandering up the path from Ellery Creek Big Hole to the car park on a warm evening in March, I was startled by the sight of an Owlet-nightjar on the edge of the path in front of me. It was surprised by my intrusion at first but I retreated slowly leaving it in the edge of the torch beam and it shortly turned away from me and continued what it was doing. What it was doing, was straddling a line of ants making their way along the edge of the concrete path and, literally, decimating them. It was repeatedly and frenetically pecking at the line of small black ants, gobbling down the hapless insects.

I’ve no reason to think that these observations are unique but still thought it worth documenting them here in case they are of any use or interest to anyone conducting further research on the species. Unfortunately, my camera was equipped with a fixed 50mm f1.2 lens for star photography so my captures of the encounter are disappointing to say the least. After a couple of almost worthless record shots I sprinted to the car for a zoom lens but was crushed to return and discover that the bird had flown.

Record shots = you *really* had to be there.

Still, it was a distinct privilege to sit with that bird for those few seconds and gain this firsthand insight into this surprising behaviour.

CBW

 

PS: I was leading this private photographic tour for Mark Carter Birding & Wildlife. We had numerous one-off wildlife encounters like this, and were able to perfect our star photography in a number of scenic locations over successive clear, dark nights. If this sort of thing is up your alley, you should get in touch with Mark and see this astonishing region with someone who knows it best. http://www.birdingandwildlife.com/

Brown Falcon and Thorny Devil - predator and prey

Herping, RaptorsChris Watson

Thorny Devil Moloch horridus, a face only a naturalist could love?

With Thorny Devil weather soon to be upon The Red Centre, I thought it timely for a re-posting of this ditty from 2011. This is an old post from the Birds Central blog archives dated 4/10/2011.

The Brown Falcon Falco berigora, may be the most common raptor encountered around central Australia; it is certainly the most common of the Falco species. It has been the cause of many mis-identifications due to the broad range of plumage colours that the species exhibits, dependent on age and sex. The bird in these pictures (below), taken on Owen Springs Reserve near Alice Springs, is toward the paler end of the spectrum which likely indicates that this is an adult male. The plumage appears darker in younger birds and may be so dark as to be mistaken for black in certain light conditions. The adult birds, with their very pale underside might be mistaken for the rare Grey Falcon F. hypoleucos, and the younger, darker birds are prime candidates for confusion with the Black Falcon F. subniger. One of the easiest field marks to look for in both cases are the feathered legs. Both the Black and Grey Falcons have fully feathered legs, whereas the Brown Falcon has completely bare, and slightly longer, legs - all the better for chasing terrestrial prey. The Grey Falcon is also distinctive for its bright yellow feet and the Black Falcon for its longer tail.

Brown Falcon Falco berigora. Note the yellow cere and orbital ring; features sometimes cited as diagnostic features of Grey Falcon which could clearly create confusion for inexperienced observers.

The Black and Grey Falcons are specialised bird hunters with a preference for taking their prey in mid-air. The Brown Falcon however, while it will also hunt and kill birds, is beautifully adapted for taking advantage of a plentiful food source in arid Australia - reptiles. Small lizards in particular, are a staple of its diet.

This bird had been hawking grasshoppers in the smouldering remains of a fire, hence the jaunty blade-of-grass fascinator.

 Around central Australia one of the commonest small lizards is this bloke. This is a famous Centralian resident, surprisingly common, but often missed due its highly effective camouflage. Both the colouring and texture of its skin make this animal exceedingly difficult to find among the sandy scrub of its home. The animal here (below), also on Owen Springs Reserve, is in its defensive posture. By adopting this pose, with the head tucked down as low as possible exposing the "false head" on the back of his neck, he hopes that a marauding Brown Falcon will attack this fatty, expendable decoy, rather than his real head. If that gives him time to scarper into the undergrowth, he will be very difficult to find indeed. Once these critters move from the open road into any sort of vegetative cover... they vanish. It's an impressive party trick.

Hunkered down, hoping you'll choose to attach the wrong head.

Up close, you'll notice an intricate network of grooves and channels running around and even across the scales. The characteristic spikes have longitudinal grooves converging toward the tip. These scales can collect dew on misty mornings, as can the feet when they are in contact with wet ground. They can channel this moisture across the reticulated grooves by capillary action where it can be absorbed through the skin. The mouth is tiny and the Thorny Devil is (as far as I am aware) incapable of biting. Their diet consists entirely of small black ants of the genera Pheidole andCampanotus

A different individual striking a more strident and characteristic pose.


All of these things combine to make the Thorny Devil one of my all time favourites. An animal that looks absolutely terrifying, but is more or less harmless (unless you're an ant), and almost defenceless. It wasn't looked on quite so kindly by early naturalists. It still has to carry that awful specific name horridus, and the generic name Moloch. This is a name with diabolical literary associations stretching from the days of the old testament, to John Milton's Paradise Lost, and even more recent pulp fiction. Moloch, in scripture and Milton's masterpiece, was first among the demons in Pandaemonium and a great warrior in Satan's army. Dan Brown (yes, he of The Da Vinci Code) gave a nod to Moloch by naming the main villain in his latest book The Lost Code, Mal'akh. Anyway, the bibical Moloch was supposedly known for his fondness of gobbling down Canaanite children like jelly-beans. When naturalists, apparently well up on their scripture, first observed a Thorny Devil poised above a line of ants sucking them into its mouth, one after another, it must have rung a bell.

The Brown Falcon on its hunting perch; how you'll most often see them in Central Australia. Note the unfeathered tarsometatarsus (lower leg) just visible.

The best way to find one is to cruise slowly along a quiet road that passes through sand country and stay alert. These little lizards are often basking on, or making their way excrutiatingly slowly across, the road when the weather is warm enough. Even in the middle of the road they are so small, well concealed, and unexpected that the majority of them end up being squashed. This is a great tragedy as this animal is one of the real postcard characters of inland Australia and something that all visitors hope to see during their stay. Many is the time I've heard a tourist wondering aloud where all these famous Thorny Devils are, when the chances are that they will have driven past at least a dozen of them between Alice Springs and Uluru, and probably twice as many squashed ones; on one drive I counted 22 between the Lasseter Highway and the King's Canyon Resort 170kms away. So in good weather, at the right time of day (mid-morning and late afternoon), you can expect one perhaps every 10kms! This is a great reason to slow down, sharpen your eyes, and try to lessen our Thorny Devil road toll.

Another aid to the Thorny Devil's crypsis, is its curious chameleon-like walk. It lurches and jerks its way across the sand it has been observed many times before, like a tiny wind-up toy. It's a puzzling strategy but I suspect it limits the amount of flat-out movement, which is the most likely thing to catch a predators eye. As you can see in the video below, if this lizard was moving across leaf litter or thick grass, the movement might easily be overlooked as leaves or vegetation moving in the breeze.


If this wasn't enough they have one more trick up their spiky sleeve. Thorny Devils have what amounts to a thumbprint, of sorts, on their bellies. All Thorny Devils can be identified to individual level by the subtle differences in the patterns on their bellies, much like the fluke patterns of Humpback Whales. As the small gallery below demonstrates, no two are the same (I have a few hundred of these belly snaps - honestly, none are the same). 

So there you go. The next time you see a Brown Falcon loitering about some sand country in Central Australia, it is very likely a Thorny Devil that is on the menu. Happy herping!

NBThank you to Paul McDonald and Stephen Debus. Paul's 2003 paper, which I was previously unaware of, shows that plumage and bare part colour variations in the Brown Falcon previously attributed to different "morphs" are most likely indicators of age and sex