Preferring life on the wing

Richard Collins marvels at the swifts’ mastery of the Iguaçu Falls and the skies

ON seeing the great waterfall at Iguaçu, Eleanor Roosevelt famously exclaimed “poor Niagara!” And well she might; the river separating Brazil and Argentina plunges over an 80 metre-high cliff in a torrent of unimaginable power. The channel is almost 3km wide and, when the river is in flood, there may be as many as 274 individual cataracts.

One interesting feature of Iguaçu goes unnoticed by most visitors. Every so often, small black birds assemble into flocks and go whirling about in the misty spray above the great falls. The birds look like locusts or swallows but they are, in fact, swifts. Known as “great dusky swifts”, they scoop up the insects which abound in the warm tropical air. Occasionally, a swift will disengage from the flock and fly straight into the torrent.

This kamikaze behaviour is the dusky swift’s great claim to fame. No bird, it would seem, could survive flying into a waterfall. But appearances are deceptive. The swifts never actually hit the water. Instead, they zig-zag between the individual flows to reach the cliff behind the torrent. To our eyes, they move much too quickly for such complex manoeuvres, but swifts live at a very different pace to humans; 10 seconds in their lives is equivalent to several minutes in ours. Weaving in and out between the jets of water, is probably just a leisurely meander to a swift.

Under the falls, the birds seek out a rock-face on which to roost. Dozens gather together, clinging like bats with their tiny feet as the great walls of water crash down just centimetres from them. Bats hang upside-down but the swifts are right-side up. Pairs nest there, laying their eggs in cups cemented to the rock with their saliva.

No location could be more secure from the birds’ enemies, but going to such lengths to roost and protect your nest seems extreme. The choice of location must surely create as many problems as it solves. Swifts, reportedly, can become trapped when the river suddenly floods, the increased flow of water sealing the openings between cascades. Keeping eggs and chicks warm in such damp conditions must be difficult and the deafening noise of falling water can’t be good for the ears of baby birds. Then there is the problem of getting the fledglings out from under the falls without their being caught by the torrent and swept to their deaths.

Extreme security measures seem to be a swift thing. For our Irish swifts, which are arriving from Africa just now, safety is also a priority. Birds of most species seek out a secluded sheltered place in which to roost at night but not our swifts. Instead, as dusk approaches, many of them climb high into the sky towards a layer of warmer air. This is usually about 1,500 to 2,000 metres above the ground but swifts have been observed from aircraft more than 3,000 metres up.

Here they spend the night sleeping fitfully on the wing. Like their cousins under the waterfalls in South America, only with such extreme measures can they feel safe from their enemies. Since it left the country last Autumn, a swift may have flown continually, it’s feet not touching a solid object for months!

The European swift’s Latin name, Apus apus, is a clue to the bird’s neurosis about safety. “Apus” means literally “no foot”; swifts’ legs and feet are tiny. The bird can’t even stand, let alone walk or run. This is a creature so well adapted to life on the wing that it has almost dispensed with hind limbs altogether. Without effective legs, the bird can’t change position to get airborne quickly when danger threatens and so it’s a sitting duck for a hawk, an owl or a falcon. Swifts may have difficulty taking wing at the best of times; if placed on the ground, this virtually leg-less bird can’t get into the air at all.

Living full-time on the wing is simply not on for a creature which lays eggs and nurtures chicks. Until they devise a way to breed while flying, the dusky swifts will just have to continue running the gauntlet of the giant waterfall at Iguaçu.


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