Edition 47: Summer 2009
Fish seems like the ideal diet: succulent slabs of protein in apparently inexhaustible abundance. But catching this slippery prey takes skill, technique and the right gear – as any long-suffering angler will tell you. Africa’s birds have risen to the piscivore challenge with ingenuity and flair. Forget the one that got away; they’re too busy downing the one that didn’t. By Mike Unwin.
Splash and grab
An African fish eagle (Haliaeetus vocifer) may seem unmissable to the human observer: it hardly takes a twitcher to identify that yelping call and snow-white head. But pity the poor barbel or tilapia, meandering downstream, blissfully unaware of its nemesis watching from above. Unseen, the eagle swoops from its perch to pluck its catch from the surface, extending long legs and fishhook-like talons just before the impact, then flapping strenuously to haul clear. Prey averages 500g in weight – anything heavier than about 2kg must be dragged across the surface to the shore. The eagle needs just one decent catch to satisfy its daily requirements. This takes, on average, just eight minutes of fishing time and is usually achieved before 10am. The rest of the day is spent preening – and no doubt gloating – as anglers sit out their marathon vigils on the bank below.
Deeper and down
If a fish eagle makes a splash, the Cape gannet (Morus capensis) detonates a veritable explosion as it drops vertically into the sea from heights of up to 30m. Unlike the land-based raptor, this big seabird does not use its feet, but turns its whole body into a fish-seeking missile – folding back its wings and hitting the surface beak-first at over 90km/h. Special adaptations enable it to survive the impact: the external nostrils are sealed shut, a special membrane protects the eyes, and air sacs beneath the skin of the neck deploy like airbags to absorb the shock. The momentum propels the bird up to 15m beneath the surface, enabling it to pursue and grab the shell-shocked fish. During the celebrated ‘sardine run’ off South Africa’s coast, Cape gannets gather in thousands to bombard the surface – the commotion alerting sharks and dolphins, which join the feeding frenzy from below.
The real slim shady
It is a bird? Is it an umbrella? What is that strange black mound shuffling across the water? A black egret (Egretta ardesiaca) out fishing is a bizarre spectacle. But watch carefully: this small, dark heron has stolen a march on the competition with a unique strategy called ‘canopying’. Having found a promising spot in the shallows, it stretches out its wings to enclose its slim body in an umbrella-like canopy – rather like a melodrama villain flourishing his cape. The shadow this casts on the water offers a tempting refuge to unsuspecting fish. Big mistake: the heron gets a perfect view as the tiddlers swim right up to its feet, and its stiletto bill snatches yet another victim. Times of plenty may bring black egrets together in loose feeding parties of 100 or more – looking like a collection of discarded bin-liners bobbing around the shallows.
If fish eagles use hooks and herons harpoons, then the fishing tackle of choice for the white pelican (Pelecanus onocrotalus) is the net. This takes the form of an expandable pouch of yellow skin, known technically as the gular sac, which hangs from the lower mandible of the bird’s 50cm-long bill and can hold up to 12 litres. A fishing pelican plunges its bill below the surface and scoops up the catch in its pouch. It then squeezes out the water, juggles the fish into position and swallows it headfirst. Where prey is abundant, white pelicans often coordinate their attack. They team up to surround the shoal in a horseshoe-shaped flotilla, using their bills and beating their wings to herd their prey into the shallows. Then – in one mass collective lunge – in go the beaks and out comes a fish supper.
Stalk and stab
No dashing aerobatics from the goliath heron (Ardea goliath). For this lanky angler – at a statuesque 150cm, the largest of the world’s herons – patience and concentration are the name of the game. It freezes in the shallows, long neck curved like a coiled spring, until prey comes within range. Then it strikes like lightning, seizing the catch in its dagger-like bill. Prey consists mostly of fish 15–50cm long, but also includes frogs and other aquatic creatures. The struggle may leave the heron’s plumage coated in fishy slime, but tiny crumbly feathers called powder down help to mop up the mess. Unfortunately, a goliath heron’s unwavering focus on the water’s surface leaves it vulnerable to attack from above: this bird often loses its catch to opportunist fish eagles, which will happily pirate any fish left unswallowed.