Table 2.

Yearly estimates of opportunity for sexual selection, partitioned into within- and between-status components. (I_{between-status}/I_males represents the proportion of the total opportunity for selection due to male–male competition. Numbers of adult males and alphas in each year as well as number of chicks assigned paternity are given in table 1. The year 2004 is excluded from variance component and I analyses because only few nests were sampled during a short field season. Results are unchanged and variance values differ by less than 0.02 if non-alpha males are further divided into ‘beta’ and ‘non-pair’ (neither alpha nor beta) status categories.)

year	average number of chicks sired			variance in reproductive success for each status class		variance components			opportunity for sexual selection			Ibetween-status/Imales
	overall	alpha	non-alpha	alpha	non-alpha	Vwithin-status	Vbetween-status	Vtotal	Iwithin-status	Ibetween-status	Imales
2000	0.43	1.22	0.19	9.01	0.43	2.44	0.19	2.63	13.17	1.03	14.20	0.07
2001	0.51	2.12	0.19	3.86	0.81	1.32	0.52	1.84	5.09	2.00	7.09	0.28
2002	0.46	2.19	0.01	5.70	0.01	1.19	0.78	1.97	5.63	3.70	9.33	0.40
2003	0.43	1.96	0.00	5.96	0.00	1.30	0.65	1.95	7.02	3.54	10.56	0.34
2004	0.15	0.80	0.00	0.69	0.00	—	—	—	—	—	—	—
2005	0.85	3.33	0.03	10.37	0.03	2.59	2.03	4.62	3.59	2.81	6.40	0.44
2006	0.78	3.10	0.00	12.89	0.00	3.25	1.81	5.06	5.34	2.98	8.32	0.36