Table 1. Variables, parameters and notations of the model.

F r	receivers’ fitness
F s	signaller’s fitness
W	value of the receiver’s response for the receiver
V	value of the receiver’s response for the signaller
C	cost of signalling
C a	cost of the attention-seeking display
C r	cost of search
a	signaller’s quality
b s	signaller’s behaviour (signal vs. not to signal)
b as	signaller’s behaviour (give ASD vs. not to give)
b r	receiver’s behaviour (search vs. not to search)
z	receiver’s response (Up vs. down)
r	degree of interaction outside the signalling game
p	the probability that the receiver locates the signaller in the presence of an ASD
q	the probability that the receiver locates the signaller in the absence of an ASD
α	the probability that the receiver locates the signaller without searching for ASDs
x	the proportion of high quality signallers in the population
H	high quality signaller
L	low quality signaller
U	up, to give the resource
D	down, not to give the resource
S	signal
N	not to signal
SA	search for ASDs
NS	not to search for ASDs
V h = V(H,U)-V(H,D)	difference in the value of the receiver’s responses for high quality signallers
V l = V(L,U)-V(L,D)	difference in the value of the receiver’s responses for low quality signallers
W h = W(H,U)-W(H,D)	difference in the value of the receiver’s responses for receivers in case of high quality signallers
W l = W(L,U)-W(L,D)	difference in the value of the receiver’s responses for receivers in case of low quality signallers
C h = C(H,S)-C(H,N)	difference in the cost of signals for high quality signallers
C l = C(L,S)-C(L,N)	difference in the cost of signals for low quality signallers
C ah = C a(H,S)-C a(H,N)	difference in the cost of attention-seeking displays for high quality signallers
C al = C a(L,S)-C a(L,N)	difference in the cost of attention-seeking displays for low quality signallers
Cr = C r(SA)-C r(NS)	difference in the cost of search for receivers