Playback experiment set up.

<p>Playback experiment set up.</p

A spectrogram of a whinny showing acoustic measures taken.

<p>A spectrogram of a whinny showing acoustic measures taken.</p

Acoustic stimuli spectrograms (a) low pitch and (b) high pitch.

<p>Acoustic stimuli spectrograms (a) low pitch and (b) high pitch.</p

Mares’ responses to playbacks (Experiment 1).

<p>Mares’ responses to playbacks (Experiment 1).</p

Acoustic (a) and physiological (b) traits of stallions (mean ± SE) (N = 15 stallions).

<p>Acoustic (a) and physiological (b) traits of stallions (mean ± SE) (N = 15 stallions).</p

Group C mares’ preference for low-pitched voices in relation with their size: tall (N = 7), short (N = 4).

<p>*Result of Mann-Whitney test: U = 3, P = 0.038.</p

Stallion’s characteristics.

<p>Stallion’s characteristics.</p

Relationships among physiological features.

<p>Relationships among physiological features.</p

Mares’ responses to playbacks (Experiment 2).

<p>Mares’ responses to playbacks (Experiment 2).</p

Correlation between voice frequencies in relation to (a) heart beat rates (P = 0.03) and (b) fertility scores (P = 0.002).

<p>Correlation between voice frequencies in relation to (a) heart beat rates (P = 0.03) and (b) fertility scores (P = 0.002).</p