Table 2. Acoustic structure of rumbles produced during pre-stimulus phases (controls), and in response to Samburu voices and bee sounds.

Acoustic variable	Rumble category	Response (mean ± SEM)
Mean F 0 (Hz)	Controls	15.3±0.6
	Samburu voices	20.2±0.8
	Bee sounds	17.5±0.8
F 0 range (Hz)	Controls	2.5±0.4
	Samburu voices	5.1±0.5
	Bee sounds	5.0±0.6
F1 location (Hz)	Controls	33.0±1.7
	Samburu voices	38.8±1.3
	Bee sounds	33.0±1.3
F2 location (Hz)	Controls	109.3±6.3
	Samburu voices	128.8±4.3
	Bee sounds	136.4±6.9