Herons and egrets

Visit any body of water almost anywhere on the planet, and you’ll certainly see a heron or an egret. The reliability with which herons and egrets can be spotted and identified across the globe is a source of great comfort to me when I travel to unfamiliar locales — no matter how far I am from the ecosystems I call home, I know that the herons and egrets are going to look roughly the same. And this dependability of herons and egrets extends to their behaviour as well — whenever I come across a heron or egret hunting for food, I can rely upon it to be thoroughly entertaining.

Herons and egrets primarily eat fish, and have devised a plethora of techniques, ranging from subtle manoeuvres to more frantic tactics, to make the task of catching fish easier. On one hand, the snowy egret uses its foot to gently stir the water in which it stands. This motion provokes nearby fish into moving, and thus into making themselves visible to the predatory bird waiting patiently above. On the other hand, the reddish egret paces frantically up and down, stopping abruptly to shelter its head with its wings as it peers keenly into the water below. This wing-sheltering behaviour helps the egret get a better look at the animals it has scared into action, before it darts its beak into the water to stab at the terrified fish that will comprise its next meal.

Some biologists believe that both the foot-stirring and wing-sheltering behaviours serve an additional, more devious purpose — to attract fish towards the creature that will soon consume them. Snowy egrets have black upper legs but yellow feet, and the movement of this brightly coloured foot in the water might lure fish towards the bird. Similarly, many fish seek out dark, sheltered spots to hide from predators, and are thus fooled into swimming under the reddish egret’s raised wings. But the pinnacle of such deception by herons and egrets is their use of actual bait — insects, berries, pieces of bread — that they collect and carefully place in the water within striking distance, ready to catch any hungry fish that comes to investigate the incongruous food source. However, it can take a while for a fish to find the bait; in the meantime, the bird meticulously repositions the bait every time it floats away, demonstrating a degree of persistence that I envy.

Rather ironically, herons and egrets themselves fall prey to the same sort of deception that they inflict upon fish, at the hands — or should I say, jaws — of alligators and crocodiles. The only aspect of a heron’s life more important than eating is successfully breeding and raising chicks. Building a nest is crucial to this process, and since large groups of herons often nest close to each other, the sticks that nests are built from are often locally in short supply. Some crocodilians take advantage of this by positioning sticks on the end of their snouts, and then pretending to be a log. In their desperate search for housing material, the birds fail to notice the suspicious-looking ‘log’ on which these sticks are positioned, and they meet their end in the jaws of a voracious crocodilian. A fitting demise, at least from the perspective of fish that have succumbed to the trickery of herons and egrets!

(ambika kamath studies organismic and evolutionary biology at Harvard Universit)

COMMENT NOW