Overview
The Horned Coot (Fulica cornuta) is an extraordinary, giant aquatic rail found exclusively on the freezing, windswept volcanic lakes of the high Andean Puna. Renowned for its bizarre, erectile black ‘horn’ of flesh and feathers that protrudes from its forehead, it is world-famous among ornithologists for an astonishing engineering feat: it builds massive nesting pyramids out of thousands of river stones carried in its bill.
Biology and Physical Characteristics
One of the largest rails on Earth, the Horned Coot has uniform dark slate-black plumage, a bright orange-yellow bill with a black culmen and tip, and dull greenish-brown lobed feet. Its most astonishing physical feature is a prominent, flexible, 4-centimeter-long fleshy caruncle (horn) topped with three small feather tufts that stands erect on its forehead and can be raised or lowered during courtship displays.
Behavior and Ecology
Because high Andean lakes lack emergent reedbeds or aquatic grasses to anchor nests against gale-force mountain winds, the Horned Coot constructs an artificial gravel island. Over several weeks, a mated pair uses their bills to carry thousands of individual volcanic stones into shallow water, piling them into a massive stone mound up to 4 meters in diameter and 3 feet tall, weighing up to 1.5 metric tons, upon which they place their weed nest.
Conservation and Human Impact
Classified as Near Threatened by the IUCN, the global population is estimated at only 10,000 to 20,000 individuals confined to a handful of fragile volcanic lagunas. The extraction of water for lithium mining, disruption by mineral extraction, and egg harvesting pose ongoing conservation challenges.
Interesting Factoid
The Horned Coot is the world’s only bird that builds its nest out of solid stone: a pair will haul over 4,000 heavy rocks in their bills to build a massive stone pyramid in the water that weighs as much as an automobile.