Andean Cock-of-the-rock

This behaviour, called lekking, is a mating strategy in which multiple males gather at a shared traditional site, each defending and displaying from his own small perch within sight and earshot of the others, rather than each male trying to attract a mate independently across a wider territory. Concentrating displaying males in one location makes it easier for visiting females to directly compare several potential mates side by side in a short visit, and it is thought that clustering may also offer some males an advantage simply by drawing more female attention to the site overall, even though only a small number of the most successful males at a lek typically achieve the majority of matings.

The large, semicircular, fan-like crest extends forward from the top of the head and can partially or almost completely obscure the bill when viewed head-on, which might seem impractical but does not meaningfully interfere with feeding, since the bird can still open its mouth and manipulate fruit and insects normally beneath the feather covering. The crest's primary function appears to be purely a visual display feature used during courtship, making the head appear larger, more colourful, and more eye-catching to females evaluating a displaying male, with the trade-off of a slightly obscured bill considered evolutionarily acceptable given the reproductive benefit of a more impressive display.

This is a clear example of sexual dimorphism driven by lek mating behaviour, since in species where females select mates primarily based on visual display quality rather than a male's contribution to raising young, males face strong selective pressure to be as visually striking as possible. Because the female alone builds the nest, incubates eggs, and raises chicks without any help from the male after mating, males invest their reproductive effort entirely into competing for matings through appearance and display rather than into parental care, while females retain duller, more camouflaged plumage that helps them stay hidden while sitting on an exposed nest and caring for vulnerable chicks.

Constructing a sturdy cup-shaped nest from mud reinforced with the bird's own saliva and plastering it directly onto a vertical rock face, cliff ledge, or cave wall, typically near a stream, provides a nesting location that is considerably more difficult for many ground-based or even some flying predators to reach compared to a nest built in more accessible vegetation. This distinctive nesting habit, which gives the species its common name in several languages referring to rocks, also tends to keep nests sheltered from heavy rain in the humid cloud forest environment where the species lives, protecting the developing eggs and chicks from the elements as well as from predation.