Guianan cock-of-the-rock

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.[7] 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.[8] Small snakes, lizards, insects and frogs are occasionally found in its diet.[7] 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.[9]

Closer view of the male's crest and ornamental feathers.

Guianan cocks-of-the-rock breed early in the year, and the females lay their eggs around March, nesting in rocky areas.[10] 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.[10] The males each have their own area on the forest floor where they make their courts. The size of each court is about 1 metre (3 ft) in diameter, and the next bird is often about 3 metres (10 ft) away.[5] The females and males live separately; only when it is time to mate do females fly over to observe and choose a male. 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.[5][11]

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, the female Guianan cocks-of-the-rock displayed sexual selection based on 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 lower-ranking single males were ignored. The rankings were determined by where the courts were positioned in the lek: courts that were more centrally placed indicated more successful and higher-ranking males.[5] The females in the study were individually observed to aggregate towards larger, more centrally concentrated leks, demonstrating active female choice.[3]

Unlike other species of the family Cotingidae, the Guianan cock-of-the-rock makes its nest on rocky cliff faces and caves rather than in the trees.[6] The female lays one or two eggs in the nest of mud and plant material, which is attached by saliva to a vertical rock. The female takes care of the building and maintenance of the nest, the incubation of the eggs and the parenting. The male does not participate at all. Eggs typically incubate for 27–28 days. The ideal nesting sites for this species are usually located 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 deposited into the crevices. Due to the solid nature of these nests, they typically persist from one breeding season to the next. Females will make repairs to their nests as the breeding season begins.[10]

Illustration by Jacques Barraband showing male plumage.

The smaller of the two cocks-of-the-rock, the male Guianan takes the lesser part in breeding. It 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 his magnificent plumage. These displays take place in communal leks, where 40 or more males may gather to challenge rivals and beckon to the females.[12][13]

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.[5][11] 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.[12][13] Males display on branches about 2.5 metres (8.2 ft) from the ground until a female approaches when the males display and call from individual plots on the ground.[14] 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.[15]

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.[16][17]

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.[18][19]

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.[20]

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.[21]

There is speculation that the simulation of male-male competition is important in lek formation and breeding.[22]

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.[20]

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.[3]