The Guianan Cock-of-the-rock (Rupicola rupicola) is a South American passerine about 30 cm (12 in) in length. The bright orange male has a prominent half-moon crest, which is used is competitive displays in lek gatherings to attract a female.

Description

The Guianan Cock-of-the-rock is a stout-bodied bird with a visible half-moon crest, an orange-tipped black tail, black, orange and white wings, and silky-orange filaments of the inner remiges. Additionally, this species also has an orange bill, legs and skin. The less conspicuous female is dark brownish-grey overall and has a yellow-tipped black bill and a smaller crest. It has a total length of approximately 30 cm (12 in) and weighs 200-220 grams (7-7½ oz).

Range and habitat

As suggested by its name, the Guianan Cock-of-the-rock is found in the Guianan Shield, occurring in French Guiana, Suriname, Guyana, southern Venezuela, eastern Colombia and northern Amazonian Brazil. Its preferred habitats are humid forests near rocky outcrops.

Behaviour

Diet

The diet of these birds consists mainly of fruits. Guianan Cock-of-the-rock are frugivorous, but data collected from droppings also suggest that this species does not exclusively consume fruits. Small snakes and reptiles are also parts of the diet of a Cock-of-the-rock. ^[2]

As noted above, the Guianan Cock-of-the-rock bird is primarily frugivorous in adulthood. By selectively feeding on nearby fruit trees and then defecating or regurgitating the seeds within the leks, these birds can actively influence the regeneration and succession of the forest habitat where they breed. ^[3]

Breeding

According to a detailed study and observation of Rubicola rubicola conducted by Gillard E. T., the Guianan Cock-of-the-rock breeds around the early months of the year and lays its eggs around March.^[4]

During the height of mating season, males gather in leks with multiple males defending a social display arena of much greater area than that of a lone male. The females and males live separately. Only when it is time to mate do females fly over to observe and choose a male with whom to mate. When this occurs, the females tap the males from behind and insemination quickly follows. When females approach a lek, the males stand firmly and present themselves rigidly. While lekking, males purposely contrast themselves from the background to attract the females. ^{[5] [6]}

Mating success is dependent on a variety of factors that range from the plumage exhibited by a male to the composition of the lek itself. In one study, female Guianan Cock-of-the-rock displayed sexual selection based off sequential comparisons or threshold standards. The hens engaged in a “pool-comparison” tactic, meaning that females chose males of higher rank in courtship. Males of higher rank were those with more matings received from other females. The females ignored lower ranking single males. The females in the study were individually observed to aggregate towards larger more centrally concentrated leks, demonstrating active female choice.

Male mating behavior

The smaller of the two cocks-of-the-rock (the other being Andean cock-of-the-rock), the male Guianan cock-of-the-rock takes the lesser part in breeding, is polygynous, and has nothing to do with nesting once mating is done. The male's energy instead is devoted to very elaborate display rituals that show off its magnificent plumage. These displays take place in communal leks, where 40 or more males may gather to challenge rivals and beckon the females.^[7][8]

The displaying male shows its crest and plumage so much that the bill and tail become obscured, almost making it difficult to recognize as a bird. Within the lek, each bird has its own perch on a low branch, with a "court" on the ground below that is cleared of dead leaves by the draughts of each male taking off and landing. They also have a variety of calls and movements, showing off the crest and elongated filaments on the rump and secondaries, and snapping their bills.^[7][8] Males display on branches about 2.5 m (10 ft) from the ground until a female approaches, when the males display and call from individual plots on the ground.^[9] The female chooses a male by landing on the ground behind a male and pecking him on the rump. The male then turns round, and mating takes place almost immediately.^[9]

Often Guianan Cock-of-the-rock males engage in courtship disruption practices. In a study conducted by Pepper W. Trail, the interactions between adult males, females, and yearlings were observed and linked to mate choice and male dispersion patterns within leks. Adult males produced this disruptive behavior with varying intensity, which depended on the situation. In lower intensity disruptions, male Guianan Cock-of-the-rock birds usually directed aggression or threats towards neighboring males, in attempts to improve or maintain breeding status and success. The males that were hassled tended to be more successful and often were disrupted with much greater frequency than males with lower mating success. Higher intensity disruptions were used by less successful males and directed towards females that wandered by. This behavior is suggested to have the effect of redirecting females towards the hassling male. Yearlings disrupted courtships of the more mature adults on the basis of practice for future courtships, since the yearlings do not possess any territory within the lek. Female disruption was an uncommon event which had little effect if any at all on the accessibility of a male. Young males of highly promiscuous species such as the Cock-of-the rock fail to mate in their first year, likely because of the fact that older more experienced males will enjoy the majority of matings. In this strong system of sexual selection, the successive breeding of dominant and aggressive males leads to high sex drives and the endurance of polygyny. A theory suggests that the selection of these aggressive males also puts a premium, or value, on female characteristics. Hence, there is a less likely occurrence of female-elicited aggression. ^{[10] [11]}

Ecological consequences

One possible advantage to lek formation in Guianan Cock-of-the-rock is severe selection and consequent rapid evolutionary advancement, all of which is possible due to the high expendability of males. Only a few males are needed to fertilize the next generation. The courtship behavior is similarly theorized to have arisen from differences in division of labor between the two sexes. Females expend their energy on building nests and rearing young, while males spend most of their time and energy of finding mates (caring for their plumage). ^[12]

Due to the fact that Guianan Cock-of-the-rock forms large leks, averaging 55 adult males, males in these display leks were especially vulnerable to attacks and predation by large snakes and other natural predators. In manipulated groups of smaller size, around 6, predation was less likely to occur, giving rise to an inverse relationship between the number and frequency of attacks and the size of leks. Thus, with a smaller frequency of attacks on the smaller group, the smaller group of Guianan Cock-of-the-rock males was less likely to spook or disperse completely as compared to a large group where a false alarm could trigger a complete flush out 90% of the time. It was found that these birds have relatively ineffective methods of anti-predation and that only social anti-predation and the infrequency of encounters with predators were keeping these lekking males alive. ^[13] Since no successful attempts to breed Guianan Cock-of-the-rock in captivity have succeeded, there is speculation that the simulation of male-male competition is important in lek formation and breeding, and that artificial environments may not properly reconstruct or imitate the natural environments. ^[14]

Nesting

Unlike other species of the family Cotinga, the Guianan Cock-of-the-rock makes its nest on rocky cliff faces and caves rather than in the trees.^[15] The female lays 1-2 eggs in the nest of mud and plant material, which is attached by saliva to a vertical rock. The male does not participate in the building of the nest or the incubation of the eggs. Eggs typically incubate for 27–28 days. The ideal nesting sites for this species can usually be sought out in a cave or vertical rock face with crevices that provide some shelter and protection from the elements. The nests themselves are solid moldings formed from mud and plant material being deposited into the crevices. Due to the solid nature of these nests, they typically persist from one breeding season to the next. However, females will make repairs to their nests as a breeding season begins. ^[4]

Status

Fairly common locally in its large range, the Guianan Cock-of-the-rock is in the category of Least Concern on the IUCN Red List of Threatened Species.

References