# Engineering Acoustics/Resonating feathers of Manakins

# Introduction

During lekking), Male
Club-winged Manakins, *Machaeropterus deliciosus* (Aves: Pipridae) alter
their secondary feathers by
hypertrophy. The oscillation
of the secondary feathers caused by the cause them to collide and
vibrate in order to produce sustained harmonic tones with a fundamental
frequency of 1500 Hz. The male manakin produces a totally unique sound
in order to attract the attention of the female. Instead of the
conventional way of using voice for sound production, he uses his wings
as a musical instrument. \[\[Image:Golden-headed
Manakin.jpg\|center\|thumb\|500x750px\|

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Figure 1: Male Golden Headed Manakin

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# Mechanism of Sonation

\[\[Image:Manakin.jpg\|thumb\|350x700px\|

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Figure 2: Phasing of sonation

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The male manakin modifies the
sixth and seventh secondary feathers, which act as a pair of coupled
resonators. The five other secondary feathers oscillate in phase with
them to result in sonation, which sounds like a ringing *Tick-Tick-Ting*
\[1\]. The series of motions involves two brief mechanical *ticks*, when
the wings are flicked and a sustained mechanical *ting*, when they are
flipped above the back \[2\]. These two sounds are not acoustically
different except for the longer duration of the *ting*. Each of them is
composed of a fundamental frequency of 1.49 kHz and its higher frequency
harmonics.

Tick-Ting video and audio
demonstration

\[\[Image:Manakin_feather.jpg\|thumb\|350x700px\|

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Figure 3 :Modified Secondary feathers

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\]\] Unlike typical secondaries, secondary feathers 1--5 exhibit
increasingly wider rachi and an
increasingly pronounced transition from continuously tapering to an
abrupt taper around the distal two-third, three-fourth and then
four-fifth for the third, fourth and fifth secondaries, respectively.
Beyond the sudden taper on the fifth secondary, the rachi bend medially.
This 'kink' in the rachis causes it to overlap and contact the rachis of
the adjacent sixth secondary feather, while at rest\[3\]. The sixth and
seventh secondaries exhibit the following distinct modification: the
rachi is thick at the base, and at approximately one-half of its length,
their width doubles and they twist along their long axis so that the
dorsal feather surface is oriented medially. The sixth secondary feather
has ridges, while the fifth feather has a curved tip \[4\]. The
innermost pair of the modified feathers (seventh secondaries) collide
across the back. Immediately following this collision, the wings shiver
laterally and medially, pulling them just millimeters apart.
Approximately 8ms later, they are
adducted to produce another
collision. The sonation tone is produced continuously throughout this
process and the feathers generate vibrations at just the right frequency
\[3\].

# Acoustic analysis

The male Manakin leans forward and flicks his wings together at a
frequency which peaks at 1500 Hz and has unusually high Q-values. This
frequency is faster than that at which a humming bird beats its wings.
The quality factor Q is a measure of the rate at which a system reaches
maximum amplitude. Using the spectral method, Q can be determined as

$Q=\frac{f_0}{BW - 3  dB, SPL}$

where f0 is the natural frequency of the system and BW -- 3 dB,SPL is
the bandwidth at 3 dB SPL below the peak. From experiments, Q factor was
found to be above 10 for all the feathers and was as high as 27. This
implies that the structures can be good biological resonators \[3\].

# Wing modification

The extra support required for such a high speed wing movement comes
from the super-sized wing bones. The ulna of the male manakin is
modified such that it has bumps and grooves to support the wings and its
width is fourfold the usual width. Another surprising modification is
that the manakin has solid wing bones, as against most birds which have
hollow bones which allow them to fly. The wings thus modified are able
to create the perfect pitch. \[\[Image:TANGARA fêmea ( Chiroxiphia
caudata ).jpg\|thumb\|350x700px\|

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Figure 4: Female Blue Manakin

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# References

\[1\] K. S. Bostwick and R. O. Prum, \"Courting Bird Sings with
Stridulating Wing Feathers,\" Science, vol. 309, pp. 736-, July 29, 2005
2005.

\[2\] K. S. Bostwick, \"Display Behaviors, Mechanical Sounds, and
Evolutionary Relationships of the Club-Winged Manakin (Machaeropterus
deliciosus),\" The Auk, vol. 117, pp. 465--478, 2000.

\[3\] K. S. Bostwick, et al., \"Resonating feathers produce courtship
song,\" Proceedings of the Royal Society B: Biological Sciences, vol.
277, pp. 835--841, March 22, 2010 2010.

\[4\]
<http://www.pbs.org/wnet/nature/episodes/what-males-will-do/photo-gallery-manakin-anatomy/955/>

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