Table 2.

The results of linear mixed models comparing the SPCC coefficients of mew calls recorded from (i) nestlings subsequently recorded as helpers and (ii) adults recorded across two adjacent seasons, with the calls of the birds heard in the initial versus next breeding season (recording stage). (Additional fixed effects: sex, relatedness between the birds being compared, the number of seasons between samples and all significant two-way interactions. A prefix of F indicates the focal bird (e.g. nestling), C the comparison bird, significant terms are presented in bold, estimates and error terms are provided for final models. Random terms fitted included nest and bird identity (Wald Z/p-value). (i) 1.45, 0.148; (ii) 3.18, 0.001.)

effect	(i) known nestlings					(ii) adults
	est.	s.e.	F	d.f.	p	est.	s.e.	F	d.f.	p
rec. stage	0.009	0.203	0.002	1,4	0.965	0.005	0.021	0.046	1,235	0.830
Fsex	0.166	0.139	1.432	1,4	0.291	0.044	0.039	1.265	1,36	0.268
Csex	0.057	0.043	1.784	1,160	0.184	0.094	0.013	48.638	1,639	<0.001
relatedness	<0.001	<0.001	0.348	1,160	0.556	−0.044	0.044	0.799	1,656	0.372
elapsed time	0.159a; 0.177b	0.415a; 0.226b	1.539	2,8	0.271	−0.047a	0.023	4.208	1,165	0.042

^a1 year difference.

^b2 years difference.