Great Dusky Swift

Fascinating facts about the Great Dusky Swift

• At 18 cm long and weighing 56–110 g, the great dusky swift is the largest member of its genus.
• When you stand at Iguazú Falls, you can actually watch a colony of these swifts swoop right through the torrent, because they choose cliffs beside or behind waterfalls as their nesting sites, proving that some birds have turned the loudest, most dangerous water flows into safe nurseries.
• In the wild these swifts hunt in airborne gangs, sometimes mixing with white-collared swifts, and their menu spans at least five insect families, highlighting how a single bird can tap a surprisingly diverse pantry while never touching the ground.
• Their call is a rapid “ti-ti-ti” that ends in a buzzing “tirr-tshaarr.”
• Although the IUCN lists the species as Least Concern thanks to its wide range across Brazil, Paraguay, Argentina and possibly Bolivia, the construction of dams could flood the waterfalls they depend on for breeding, showing how a seemingly stable bird can be vulnerable to a single human infrastructure change.

At a glance

About the Great Dusky Swift

The great dusky swift (Cypseloides senex) is the largest member of its genus, a sleek 18-centimetre bird weighing between 56 and 110 g. Its chocolate-brown crown and throat are edged with pale gray, giving the face a frosted look, while the back deepens to a darker brown and the rump settles into an intermediate shade. The tail is a muted black-brown and the underparts a softer brown, with the upper wing surface matching the back and the underside a touch lighter. Juveniles echo the adult’s palette but sport pale fringes on their wing feathers, a subtle clue to their age. In the mist-laden forests of Brazil, Paraguay, and Argentina’s Misiones Province, these swifts make their homes among tropical evergreen and temperate forests, often nesting in massive colonies on cliffs beside waterfalls. Their nests, moss and pebbles bound with mud, cling to the sheer rock face, a testament to their adaptation to the spray-soaked environment. Ever-in-flight, they chase insects aloft, feeding on at least five insect families, sometimes mixing with white-collared swifts. A distinctive vocal signature, a rapid “ti-ti-ti” followed by a buzzing “tirr-tshaarr”, echoes over the falls, a reminder that even in the roar of Iguazu’s waters, these aerial hunters remain ever-present, their lives tethered to the cascading water that defines their breeding and roosting sites

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