Mechanism:

The question of ‘Mechanism’ seeks to determine what biological and physiological structures and systems, such as hormonal influence, neuronal activity, and genetic process, underlie a behavior (Ryan, Wilczynski)

Creating Displays

Testosterone is crucial for activating androgen receptors that allow male golden collared manakins to perform optimal courtship displays (Schlinger, 2013), and that exogenous testosterone treatment can activate courtship in adult males during non-courtship seasons (Day, 2006). However, breeding males exhibit highly variable levels of testosterone throughout the courtship season (Day, 2006). Additionally, exogenous doses of testosterone at the middle of the mating season do not increase measured display components of courtship (Day, 2006). It is thus hypothesized that the gonads of golden collared manakin males begin secreting testosterone in late January at the start of the mating season (Day, 2006). In studies of the spinal cords of female and male golden collared manakins, [H] testosterone hormone was found to be much more highly concentrated in the spinal cord motoneurons of male golden collared manakins than females (Shultz, 1999) This suggests [H] testosterone may drive the sexually dimorphic muscle movement of wingsnaps in males. Muscles involved with lifting and retracting the wing such as the supracoracoideus (SC) and the scapulohumeralis dorsalis (SD) muscles involved in bringing the humerus forward and backward are thought to control the wingsnap mechanism (Schultz, 2001). In situ hybridization studies combined with retrograde motoneuron labelling shows the SD muscle responsible for the wingsnap are innervated by androgen-receptor expressing motoneurons (Schultz, 2001). This suggests that the wingsnap mechanism in male courtship is under the influence of androgen hormone (Schlinger, 2001).

Chart of courtship behavior
Figure 1. Chart of the average courtship behaviors per minute of filming in captivity for adult courting males given either a Testosterone pellet (T) or an inert pellet (C). Shown are wingsnaps (wing), rollsnaps (roll), and snips. No differences were significant, which demonstrates that exogenous doses of testosterone given in the middle of courtship season does not lead to an increase in courtship behaviors, despite B showing a clear increase in testosterone levels.

A New Type of Song

During active courtship of a female, male golden-collared manakins extend their yellow throat feathers past their bill, jump up and down the length of their perch or lek area, and flit from branch to branch or branch to forest floor (Chapman, 1935). This dance includes loud acoustic signals termed “wing-snaps” that are produced by the upward flips of the wings, and by the beating of primary and secondary wing feathers together (Chapman, 1935). Primary and secondary wing feathers of males differ significantly from those of females and have curved, heavy and stiffened vanes (Chapman, 1935). Wingsnaps can occur either in a very loud single snap, a snapping whirr, or a rollsnap that is produced by a rapid series of singular wingsnaps (Bostwick, 2003). Golden collared manakins produce single wingsnaps as they begin jumping to court a female, and they extend their yellow throat feathers by turning in midair to face the female (Schlinger, 2013). Altogether, the entire display sequence lasts roughly 9 seconds (Schlinger, 2013).

Manakin splays wing
Figure 2. CAPTION