Behaviour patterns and their function in the Horned Screamer

Abstract

After sunrise Horned Screamer Anhima cornuta pairs give territorial declaration calls in response to the calls of neighbouring pairs. The buff-colour wing patches, normally hidden by the long contour feathers, were exposed and the head was thrown upward in a bobbing motion. These calls and displays were performed at greater intensity when a conspecific approached or entered the territory. Body postures were made conspicuous during aggressive attacks; the body was turned parallel to the opponent, buff-coloured patches on the wings and shoulders were exposed, and wings were held to the side of the body displaying the wing-spurs. Several appeasement behaviours have developed. A non-aggressive stance, head pointed upward, was held while bill-clicking. Wing-shuffling and preening behaviours covered the buff wing patches and hid the wing-spurs. Our findings support the hypothesis that coverable coloured patches have evolved as signals of threat if exposed and submissiveness if covered. Pair bond behaviours were closely associated with the 'ugh' call emitted from subcutaneous air sacs on the neck. The behaviours included mock-preening, allopreening, and head-arching directed toward the mate. The copulatory sequence entailed precopulatory calling, nest building movements, a short flight to the nest site, a side by side walk, and a crouch. While the male stood on the female's back he nibbled her neck, trod and shuffled his tail. We observed no post-copulatory display.