Honest vocal signalling

Question 1

Honest signals

Answer 1

• signals can be costly
• work if they are honest

1. production costs
2. developmental costs
3. maintenance costs

Question 2

Unforced honesty

Answer 2

• interest of sender and receiver are congruent
• sender closely related to receiver or have overlapping interests
• e.g. waggle dance

Question 3

Forced honesty

Answer 3

• occurs when interests of sender and receiver are incongruent
• maintained using index signals and condition

Question 4

Vocal signalling

Answer 4

• interacting with a specific individual, advertising territorial ownership e.g. attract mate, Tungara frog, meerkat cryy

Question 5

McComb et al (1994)

Answer 5

• lions
• loud calling, not just to mark territory, but to attract mates and allow social competitors to maintain contact when long distances
• female lions played recordings of 1/3 lionesses
• defending adult females likely to approach for 3 intruders compared to a single intruder OR more cautiously

Question 6

Source-filter model

Answer 6

The source–filter model of speech production models speech as a combination of a sound source, such as the vocal cords, and a linear acoustic filter, the vocal tract (and radiation characteristic). An important assumption that is often made in the use of the source-filter model is the independence of source and filter. In such cases, the model should more accurately be referred to as the “independent source-filter model”

• complex vocal signalling is a signal of fitness
• larynx produces a boring voice signal, but vocal tract can change shape and produce different sounds
• birds have a syrinx

Question 7

Formants

Answer 7

• groups of selectively enhances harmonics in speech and signal

Question 8

Reby and McComb (2003)

Answer 8

• looked at whether the filter in red deer is an indicator of fitness
• prediction - larger animals have a larger vocal tract, so therefore produce lower pitches with lower vocalisations of F0
• red deers are able to drop their highly mobile larynx towards their sternum, to allow an increase in vocal tract length whilst vocalising
• red deer roar repeatedly during autumn breading season (rutting season)
• influences mate attraction and advance ovulation
• gives off an impression of being larger
• aim: age, body weight and reproductive success correlated with F0 and formant frequency at maximum vocal tract extension
• method - roars recorded in red deer between 1976 and 1999, and divided into adults and subadults. The adult subset included 24 harem holding
• found that F0 was on average higher in younger stags (age), but did not decrease with body weight significantly
• BUT the minimum formant frequency reached the mobile larynx was more detracted to sternum decreased with body weight and age, and was negatively correlated with reproductive success
• therefore, F0 does not predict fitness related characteristics, but formant frequencies are a reliable cue to fitness (stag age, body size and reproductive success)
• HONEST SIGNALLING

Question 9

van Dommelen (1993)

Answer 9

• male vocal folds are longer than female vocal folds, and average pitch is half that of womans
• more growth of male larynx during puberty
• sexual dimorphism evolved since split from chimpanzees
• found no correlation between body size and pitch in men, so pitch is not a reliable indicator of body size or testosterone levels
• but listeners treat it as such (Smith et al, 2003) … cultural construct?

Question 10

Evans et al (2008)

Answer 10

• found a correlation between testosterone and pitch, but only in morning
• weak negative correlation between formant dispersion and testosterone levels
• relationship between oestrogen and progesterone and pitch even more unclear
• • female pitch is culturally determined e.g. in Japan higher pitch, or inflection at end of sentences in Australia - also depends on menstruation cycle
• unclear about honesty of indicators of fitness in male voices