Guianan cock-of-the-rock

Species of bird

The Guianan cock of the rock (Rupicola rupicola) is a species of cotinga, a passerine bird from South America. It is about in length and weighs about It is found in tropical rainforests, near its preferred habitat of rocky outcrops. The female's plumage is brownish/dark smokey grey in colour, and generally less noticeable than the males because of their nesting work in rocky areas. The male's feathers are a bright orange. Both have a heavy body, broad based bill and wear a remarkable half moon crest on the head. It is one of two species of the genus Rupicola, the other being the Andean cock of the rock. The Guianan cock of the rock lives across the forested region of northeastern South America. Its diet consists mostly of fruit, but they sometimes feast on small snakes and lizards. The Guianan cock of the rock breeds in the early months of the year and, on average, the female lays her eggs around March. The females choose a mate by flying down to the ground and pecking the male on his rump. The male then turns around and the mating takes place almost immediately. During the height of the mating season, males engage in competitive displays in the lek, which is a complex courting behaviour that is done to attract females. Males and females live separately except when the females choose a mate. The mating success varies based on multiple factors, ranging from the plumage exhibited by a male to the composition of the lek itself. There is speculation that the male–male competition is an important factor in lek formation and breeding. The main predators of the Guianan cock of the rock are harpy eagles and black and white hawk eagles.

The Guianan cock of the rock is a stout bodied bird with a prominent half moon crest. It is a sexually dimorphic bird. The male's crest is more pronounced than the female's and is bright orange. The males also have an orange tipped black tail, black, orange, and white wings, a bright orange bill, an orange iris yellowing as it nears the outer edge, and silky orange filamentous feathers of the inner remiges. Both sexes also have orange legs and skin. The less conspicuous female is dark brownish grey overall and has a yellow tipped black bill, a duller orange iris, and a smaller crest. One year old juvenile male looks similar to an adult female but has orange speckles over its body. After two years, the juvenile males become mostly orange with brown and grey spots. Males attain their definitive plumage at around three years. Juvenile females look almost identical to their adult counterparts. Guianan cocks of the rock have a total length of approximately and a total weight of around The two species of cock of the rock are allopatric, and therefore do not meet with one another. The plumage of the male Andean cock of the rock is redder and its wings are mostly black, lacking the orange colouration seen on the male Guianan. The female Andean cock of the rock is reddish brown rather than the brownish gray of the Guianan.

The Guianan cock of the rock is one of two species of the genus Rupicola. It was described by Carl Linnaeus in 1766 as the type species of its genus. Its closest relative and congener, the Andean cock of the rock (Rupicola peruvianus), is similar in body shape and colouration,

The diet of the adult Guianan cock of the rock consists mainly of fruits meaning they are frugivorous. Up to 65 species of fruit have been reported in their diet, primarily from canopy trees or lianas. Three quarters (75%) of the fruit eaten by the Guianan cock of the rock at one study site were either black or red coloured fruit. In British Guiana, E. Thomas Gilliard found papayas growing at the base of a huge rock. On top of the rock were perched females that were nesting. He found that no other papayas were growing in that part of the forest and speculated that the perched females ate papayas in the forest where they are native and dropped the seeds below where they were nesting. Small snakes, lizards, insects and frogs are occasionally found in its diet.

Guianan cocks of the rock breed early in the year, and the females lay their eggs around March, nesting in rocky areas. During the height of the 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 displaying male purposely contrasts himself from the forest, shows his crest and plumage so much that the bill and tail become obscured; almost making him difficult to recognize as a bird, to attract females. Within the lek, each female has her own perch on a low branch, while the males own a "court" on the ground below that is cleared of dead leaves by the draughts of each male taking off and landing. The males have a variety of calls and movements, showing off the crest, elongated filaments on the rump, secondary feathers, and the snapping of their bills. Most males copulate with only a few females. However, some are very successful and may copulate with many. Unlike many other bird species, the male does not use resources nor parental care to entice females. Males often 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 behaviour with varying intensity, which depended on the situation. In lower intensity disruptions, males usually directed their 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 who wandered by. This behaviour is suggested to have the effect of redirecting females towards the hassling male. Yearlings often 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 that had little, if any, effect on the accessibility of a male. Young males of highly promiscuous species such as the Cock of the rock often failed to mate in their first year, probably because 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. Male Guianan cock of the rock "delight in homosexuality" with almost 40 percent engaging in a form of homosexual activity and a small percentage never copulating with females.

One possible advantage to lek formation (in Guianan cock of the rock and other species) 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 behaviour is similarly theorized to have arisen from differences in the division of labour between the two sexes. Females expend their energy on building nests and rearing young, while males spend most of their time and energy on finding mates and caring for their plumage. Guianan cocks of the rock form large leks, averaging 55 adult males. The 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, due 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 Guianan cock of the rock males were less likely to flush or disperse completely as compared to a large group where a false alarm could trigger a complete flush 90% of the time. It was found that these birds have relatively ineffective methods of anti predation and that social anti predation and the infrequency of encounters with predators were keeping these lekking males alive. There is speculation that the simulation of male–male competition is important in lek formation and breeding.

The colouration of the males allows them to visibly stand out from the brown forest floor. This bright colouration provides a sexual advantage for adult males, increasing their likelihood of successfully mating. The result is rapid evolutionary selection within the species for brighter plumage and more conspicuous behaviour patterns in the males. The bright colouration also makes the males more susceptible to predation. Males are more expendable for this reason; only a small number of males are needed within any generation in order to perpetuate the species. While sexual selection leads to bright plumage, natural selection, in turn, favors defensive colouration in the birds. There is higher fitness in birds monitoring nests whose colouration acts as camouflage protection from predation.

In larger lek groups, there is less risk of predation. In a group, there are more individuals to alert the group about an approaching predator. All the birds in the groups will be vigilant in looking for a predator because there is an advantage to seeing the predator first. There is also the risk that in a bigger group, there will be more false alarm signals. The common signal is vocalization, after which the birds will fly up into the trees. It was found the birds did not, however, give this signal when there was a snake.