Table 1. Effects of time period, type of playback and their interaction on the proportion of time spent in vigilance, the bite rate, the step rate, the time spent in vigilance while chewing and the time spent in exclusive vigilance, controlling for the effects of date, group size, distance to cover, and grass height.

Activity	Variables	numDF	denDF	F-value	p-value	Coeff ± SE
Vigilance	(Intercept)	1	100	614.309	< 0.001	0.288 ± 0.022
	Time period	1	100	0.028	0.867	See Table 2
	Playback	2	42	3.628	0.035	See Table 2
	Time period × Playback	2	100	4.631	0.012	See Table 2
Bite rate	(Intercept)	1	92	2819.501	< 0.001	69.279 ± 7.693
	Time period	1	92	14.795	< 0.001	See Table 2
	Playback	2	42	1.750	0.186	See Table 2
	Time period × Playback	2	92	3.107	0.049	See Table 2
Step rate	(Intercept)	1	84	235.305	< 0.001	1.104 ± 0.145
	Time period	1	84	4.194	0.044	See Table 2
	Playback	2	41	2.113	0.134	See Table 2
	Time period × Playback	2	84	6.560	0.002	See Table 2
Vigilance while chewing	(Intercept)	1	75	891.392	<.0001	0.983 ± 0.061
	Time period	1	75	1.7833	0.1858	See Table 3
	Playback	2	48	0.8319	0.4414	See Table 3
	Time period × Playback	2	75	5.2121	0.0076	See Table 3
			Df	LRT	p-value	Coeff ± SE
Exclusive vigilance	Time period		1	18.505	< 0.001	See Table 3
	Playback		2	69.941	< 0.001	See Table 3
	Time period × Playback		2	13.804	0.001	See Table 3

The proportion of time spent in vigilance was ArcSinSqRoot transformed and step rate and the time spent in vigilance while chewing were log-transformed. See Tables S1, S2, S3 and S4 for details on factors that were controlled for. The pre-playback period and the control playback were used as references for the time period and playback variables, respectively. Vigilance, bite rate, step rate and vigilance while chewing were analyzed using linear mixed-effects models and exclusive vigilance using zero inflated Poisson mixed-effects models (see methods).