Guanay Cormorant

Fascinating facts about the Guanay Cormorant

• A single guanay cormorant can stretch up to 78 cm from bill tip to tail tip.
• During breeding season, colonies can cram up to three nests into every square metre of flat guano-lined rock. That density rivals a packed concert hall, turning remote islands into bustling factories of bird life. It highlights how the species turns waste into real estate, turning guano into both home and fertilizer.
• Each clutch holds two or three eggs that measure 63 mm by 40 mm.
• From an estimated three million birds in 1984, the population has slipped about 30 % due to habitat loss and over-fishing, nudging the species toward near-threatened status. That decline equals losing roughly one-third of a stadium-full crowd of birds, underscoring how human pressures can swiftly erode even abundant marine life.
• When the Inca ruled the Andes, they guarded these birds so fiercely that disturbing a guanay cormorant could be punishable by death, because its droppings were an important source of fertilizer.

At a glance

About the Guanay Cormorant

The guanay cormorant, Leucocarbo bougainvilliorum, commands attention along the Pacific shores of Peru and northern Chile with its striking black plumage punctuated by a crisp white belly and throat patch. Measuring 71–78 cm from bill tip to tail, it bears a grayish bill tipped with red, a vivid red face encircled by green, and orange-pink feet that flash against the dark feathers. Its silhouette, larger than the similar rock shag, is unmistakable when it swoops over the cold, nutrient-rich waters of the Humboldt Current, diving to pursue swarms of Peruvian anchoveta (Engraulis ringens) and silversides (Odontesthes regia). While most cormorants are known for their sleek, water-repellent feathers, the guanay’s most surprising trait is its role as the principal producer of guano, a fertilizer so valued that Inca rulers allegedly declared any disturbance of the birds punishable by death. Breeding is a year-round affair, peaking in November and December, when the birds construct nests of compacted guano on flat offshore islands or remote headlands, sometimes packing up to three nests per square meter in dense colonies. The female lays two to three eggs, each about 63 × 40 mm, and both parents share incubation duties. After fledging, the young disperse widely, with occasional sightings as far north as Panama and Colombia, likely driven by El Niño-induced food shortages, before the species settles back into its preferred shallow seas and rocky shorelines, ever-watchful for the next anchovy bloom.

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