Function of Crest Displays in Royal Flycatchers (Onychorhynchus)

Abstract

Royal flycatchers (Onychorhynchus coronatus and 0. mexicanus) of neotropics have large, brilliantly colored, fan-shaped crests that are usually concealed but can be erected perpendicularly to axis of head in both sexes. Hand-held birds spread their crests and slowly wave their heads from side to side with open bills (Bangs and Barbour 1922, Wetmore 1972, Dick and Mitchell 1979) in a manner convergent with snake of hole-nesting tits (Sibley 1955). Within family Tyrannidae (375 + species), both details of crest elaboration and head-waving behavior of royal flycatchers appear to be unique. In this paper, I examine hypotheses concerning adaptive function of crest displays in royal flycatchers and report new field observations, including simultaneous display of a hand-held pair. The crest display of hand-held royal flycatchers was aptly described for a Panamanian bird (0. mexicanus) by Wetmore (1972, p. 499), I held bird in my hand it spread crest widely and threw it far forward, at same time compressing nape feathers laterally into a straight sharp edge down back of neck. The bird rotated head from side to side in a swinging motion during which it turned through an arc of 1800. With this bill was opened widely, and tongue flicked.... On 1 July 1977, I mist-netted a male and female O. coronatus together in forest understory on alluvial plain of Rio Heath, Department of Madre de Dios, Peru. When removed from holding bag and held together facing one another, birds began immediately to perform a synchronous but out-of-phase head-waving display (Fig. 1). After 15-20 sec, birds were held closer together at a distance of a few centimeters. They locked bills and synchronously rotated their heads back and forth 1800. After several minutes, neither individual could be induced to perform. The display was not accompanied by vocal hissing, which is often produced by hole-nesting birds to discourage predators (Sibley 1955). Bill locking during courtship is unknown in tyrannids (Smith 1966), which suggests that it could have been a mutual attack. However, birds did not peck at extended fingers or camera lens. The crest displays of hand-held royal flycatchers have also been observed in mist-netted birds of both sexes in Guyanas (Dick and Mitchell 1979), on Rio Xingu in eastern Brazil (pers. observ.), and in northern Peru and southeastern Paraguay (M. Foster, pers. comm.). Geographic or sexual variation in behavior, if any, and its ontogeny are unknown. Dick and Mitchell (1979) interpreted this stereotyped behavior as an instance of Batesian mimicry; potential predators are repelled by appearance of bird. Wetmore (1972) suggested that while crest display may represent a threat function, it might be result of a nervous reaction to being handled or presented otherwise in normal courtship display. Despite extensive geographic ranges of royal flycatchers, published observations of crest displays in free-living birds are limited to Skutch's (1960) anecdotes of O. mexicanus in Costa Rica. He observed crest erection several times by preening birds of both sexes, by males during agonistic interspecific encounters, and by males displaying to females building nests or attending eggs. Skutch (1960, p. 525) noted one such display, the [male's] crest was spread widely while he preened. In middle of morning he came with his mate when she returned from an excursion for finding food. Alighting on a vine near nest, he spread his scarlet diadem to full and turned his head from side to side so rapidly that feathers quivered. At same time, he shook his half-opened wings, fanned out his yellowish tail, and uttered a rapid series of peculiar notes, somewhat like usual piping call but sharper. This superb display, only one I have ever seen in many hours of watching Royal Flycatchers, lasted only a few seconds. Skutch (1960) concluded that principal function of crest was in courtship displays. Skutch's observation includes two of principal elements of crest display of hand-held birds: (1) crest erection; and (2) side-to-side motion of head. This suggests that snake-like behavior of hand-held birds may be derived from courtship behavior. Concealed crown patches occur widely within Tyrannidae, including genera closely related to Onychorhynchus (Traylor 1977). Crown feathers are raised most frequently during intraand interspecific agonistic encounters. Smith (1966) suggested that exposed crown feathers of Tyrannus spp. open and convey a message of aggression by doubling number of open mouths seen by signal recipient. Although elaborate crest of royal flycatcher might provide a supernormal gape mimic during intraor interspecific interactions, most of which are aerial, there 'Received 19 July 1989. Final acceptance 15 December 1989.