It’s a battle of wits between a heron and a school of whitebait in the shallow waters of Cornelian Bay. A contest in which two lifeforms compete using their mental abilities and quick thinking to gain an advantage, to win, or lose. For the fish, it’s just being wary, a matter of life or death. With the white-faced heron, it emphasises intellectual prowess, strategic thinking, and the ability to react quickly and cleverly to a given situation.
Most importantly, the shrewd heron must overcome refraction, the distortion that skews an object – like a heron beak – when it is thrust into water.
Science, or more precisely physics, was at play when I came across a heron stalking fish in the bay. The heron stood motionless, its lithe body reflected in the still waters on an incoming tide.
No luck at this spot, so the heron raised a gangly leg and moved forward into deeper water as if in slow motion. It paused again, the heron’s dagger beak poised at a slight angle. The minutes passed and then there was a sudden flurry. The heron struck in a lightning movement and in a spray of water pulled its head upwards, a silvery fish wriggling in its beak. With a gulp the whitebait slid down its throat.
White-faced herons are common in coastal areas, coming into the suburbs of cities like Hobart to hunt metallic skinks sunning themselves on log piles in spring, or even on occasion raiding fish ponds in gardens for goldfish.
But it is out on estuary and coast, in saltmarsh or on mudflat that the delicate art and craft of the heron is best appreciated.
Acquiring the necessary fishing skills must present a steep learning curve for young herons. The first lesson is not to be bamboozled by the phenomenon in which light travels slower through water than through air, so a straight object appears bent when it breaks the water’s surface. Underwater, objects appear closer than they really are, so herons need to learn to make allowances. To hit, they must aim to miss, though by how much depends on the depth of the water. The problem is minimal when the bird’s line of sight is directly above its prey, but that’s when it’s most likely to be spotted by a fish. The best compromise is that shallow angle of approach, delaying that downward strike as long as possible.
Surface reflections can also be confusing for herons. Turbid water after heavy rain clouds vision.
I never tire of looking at herons and the closely related egrets also found in Tasmanian waters. Graceful and elegant, the white-faced heron’s blue-grey feathers carry a pink sheen on the breast and a mask of white which gives them their common name. But I prefer a second – that of blue crane.