P1000: Getting a closer look at Darters (aka Snakebirds or Anhingas)

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Roof Rack Junior Member • Posts: 32
P1000: Getting a closer look at Darters (aka Snakebirds or Anhingas)

Be advised that this is a long, wordy post.

The simple but exciting reach provided by the P1000 enabled me to have a closer look at an intriguing bird, the Australian Darter (Anhinga melanogaster) on my first outing with the new camera. The Darter is widely distributed across Australia’s wetlands, but it is rarely abundant and rather people-shy. Because of its almost unique mode of living, it is neither well observed nor understood. It is an unusual bird, being a subsurface fish spearer, a lifestyle I find intriguing. This Post tries to explain why this bird intrigues me.

A surfacing Darter in the Mary River, ‘Top End’ of Australia. This river is highly productive of fish, both large and small species, and consequently has one of the world’s highest densities of crocodiles – an adult crocodile every 200 metres. I shot this image from a specially located crocodile-viewing platform (visible on Google Earth at -12.486567, 131.7232). This bird was industriously diving in a river where any person who, ignoring the numerous warning notices, goes swimming, wading, or even camping by the water’s edge would likely have a terminal experience and immediately qualify for a Darwin Award for Outstanding Stupidity (https://darwinawards.com).

Two questions: Was I just watching one bird’s risky and perilous behaviour, or does this species enjoy immunity from crocodile predation?

And, how does this bird locate its target fish in this turbid water where visibility would be less than 10 centimetres (4 inches) at the surface?

I tried to answer the first question over the next few days at a nearby billabong (aka Oxbow, Google Earth at -12.660229, 131.711206). This shallow, non-flowing waterbody is filled by overland flooding during ‘The Wet’ (December- April), then slowly shrinks during ‘The Dry’ (May- November), becoming a focus for increasing hundreds of waterbirds. I was informed that it has never dried out.

Mid-morning at the billabong. The temperature was about 35°C (95°F) but the birds (Magpie Geese and Whistling Ducks) were clustered either on the shallow water’s edge or in tree shadows (LHS top), not actually in the water. No Darters were in this bird gathering. Because not one swimming bird was out on the billabong surface, I assumed that this was because of the presence of crocodiles.

All actively feeding birds were concentrated on land at or near the water’s edge. Some like these (mud-stained) Magpie Geese were prepared to stand and preen in water about 10cm (4”) deep. The only bird that was actively feeding in deeper water, but not swimming, was this Royal Spoonbill (Platalea regia).

The billabong had a very visible population of both the crocodile species found in Australia as illustrated in this composite, unscaled image. The top image is of a 2.5 metre ‘Saltie’ (Crocodylus porosus), a species tolerant of saltwater but found mainly in freshwater, well known for predating large livestock (buffalo, cattle, horses), wallabies, fish, and occasional fishermen. It has been frequently reported as taking large waterbirds, including the Jabiru, a native stork. The bottom image is of a ‘Freshie’ (Crocodylus johnstoni), a slightly smaller animal found only in freshwater, with a long narrow snout. Primarily a fish eater, it has often been observed taking unsuspecting waterbirds, principally herons.

Unsurprisingly, just during the four days visiting the billabong, I did not witness any birds being taken by crocodiles. Both crocodile species are superb stalkers of their prey, either on the surface or submerged, and their reaction times are lightning fast. This is emphasized on the warning notices displayed for tourists: “The crocodile will see you long before you see the crocodile”. To illustrate the stalking and reaction times crocodiles show when taking birds, this professionally-shot video captures Freshwater crocodiles catching flying bats – a favourite food item (https://youtu.be/wi30w-Mk2yQ).

The billabong was just over 1 kilometre long, about 100m wide and mostly about 2-3m deep. About 6-8 Darters were encountered along its length compared with many hundreds of the other foraging wetland birds along the water’s edge, such as ‘geese’, ducks, herons, egrets, etc. It was obviously a very productive waterbody and exemplified by the number of a large eating fish (Barramundi) caught each day by our off-duty guides. Crocodiles big and small were always encountered (but not counted), such as this 2 m ‘Saltie’ crossing in front of the boat.

The Australian Darter: an immature female (?) in alert mode in the company of two mud-stained, uninterested Magpie Geese. This silhouette pose reveals how these birds are streamlined by a conical body shape for underwater fishing with the paddling legs positioned well to the rear to maximise propulsion. Though not clearly visible here, all four toes are webbed together, compared with just three in ducks and geese. However, the benefit of having large area paddles or ’swim fins’ comes with two costs: wide flat feet are poor graspers of perches, and even with toes and webbing folded together, it is difficult to run quickly on land. This flat concrete paver would be the most comfortable place for a Darter to stand. Two other points of interest here are the needle-sharp beak and the prominent ‘wish bone’ in the chest. I suspected that the hollow area above the ‘wish bone’ indicated this bird was (comparatively) poorly nourished.

A suspicious young immature female (?) having almost completed drying its feathers. This bird claimed this perch and could always be found here according to our guide. The diameter of the perch was about as small as can be securely grasped. This bird appeared in better condition than the bird with the prominent wish bone.

An adult male (?) but without the brown chest feathers of the breeding plumage. The thick, rigid tail feathers are extraordinary for a bird, and it’s neck is folded into a perfect S-bend that all plumbers would be proud of. The wings were outstretched not to dry them but to balance its waddling gait. Note how even with toes and webbing folded, each step requires moving a large-area ‘clubbed’ foot.

A mature-aged female, apparently well fed, in the neck-coiled resting position. According to our guide this was this bird’s permanent perch, so the mature birds must seek, hold and be able to defend territory.

In the few days with Darters, I was unable to prove, or disprove the proposition that ever-present crocodiles do not take Darters. However, with the reach of the P1000 I was able to better see and understand this interesting bird’s behaviour. I am still learning how to better use this camera and planning a return visit to the billabong.

Nikon Coolpix P1000
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