Skimming the surface
Seeing is believing: Mike Unwin cherishes the fly-by of his high-speed fisher friend
“Chip-chip, chip-chip.” A high-pitched, yapping call heralds a familiar evening fly-past. I look up to see four birds appearing around the bend, their long, elastic, wings reflected in the river’s dying gleam. It’s my dusk alarm call: an announcement that darkness is falling and that I’d better get back indoors before the hippos start wandering about. The sound follows me as I hurry home: “Chip-chip, chip-chip.”
During a three-month stint on a safari camp beside Zambia’s Luangwa River, many years ago, I came to associate the distinctive flight call of African skimmers with the end of my working day. At around 6pm every evening the birds would fly upriver, past camp; you could set your watch by it. At the time, I imagined that they were returning to their nests after a long day’s fishing. In fact, they were just heading out.
You needn’t hear a skimmer’s flight call to identify it. One glance reveals that this unusual bird has something decidedly odd about its bill. Not only does the bright-orange appendage seem disproportionately large, as though the bird is clutching a carrot in its mouth, but – uniquely among birds – its lower mandible extends a full third longer than the upper. Bill aside, this is an elegant bird, its graceful lines and buoyant flight revealing its affinity to terns. But let’s be honest: it’s hard to get beyond that bizarre conk.
If bird’s bills are tools, each adapted a specific job, few are more specifically adapted than a skimmer’s. The clue to its function is in the name: flying low over the shallows in a straight line, this bird skims its lower mandible just below the surface, slicing through the water like scissors through silk to leave a neat, V-shaped wake.
The instant it comes into contact with a fish, the upper mandible (maxilla) snaps shut by involuntary reflex to secure the prize. A muscular shock-absorber system cushions the bird’s head and neck against the sudden impact.
Skimmers feed in still, shallow water, where small fish such as cichlids or tilapia crowd near the surface. Because their feeding technique is largely tactile, they have no need to see their prey and thus do much of their fishing at dusk, dawn and during the night. At these hours, they face less competition from other fishers, and their large eyes allow them to navigate in half light.
The African skimmer is one of three very similar species worldwide, the others being the Indian skimmer of Asia and the black skimmer of the Americas.
Like its cousins, it frequents slow-flowing, tropical rivers, with shallow stretches in which to fish and sandbanks on which to nest. Pairs are monogamous, and after reaffirming their bonds each year via a noisy, aerobatic courtship display, they scrape a shallow depression in the sand for their clutch.
Incubation is shared between the two, with the damp sand keeping the exposed eggs cool in the baking African heat. The parents defend their nest vigorously, dive-bombing animals as large as elephants or buffalos that wander too close – and the young hatchlings will even bury themselves in the sand when danger threatens.
Nesting so close to water, river levels are a critical factor in the life cycle of skimmers and determine their migratory movements around the continent.
In southern Africa, these birds are winter visitors, arriving in the May–June dry season, when water levels are falling, to breed on the exposed sand banks. Come the rains in November, when rivers rise and sand banks are submerged, the young have already fledged and the birds are preparing to return north. In East and West Africa, where rainfall patterns are different, skimmers breed during the March–June low-water months.
This species has a wide but patchy distribution across sub-Saharan Africa, from Senegal and the southern Nile valley in the north to northern KwaZulu-Natal in the south. Large, slow-flowing rivers such as the Chobe, Zambezi, Luangwa and Rufiji all host breeding populations, and the Okavango Delta is another good spot. The bird is nowhere common, however, and it faces a number of threats, including river pollution and the wash of careless power boats, which may swamp entire breeding colonies.
Today the IUCN lists the African skimmer as Near Threatened, with an estimated population of 15–25,000 mature individuals.
Back in the UK, I no longer get that ‘chip-chip’ signal to knock off work. But downing tools at 6pm generally seems a good idea. Besides, you can never trust those hippos.