Table 1.

Results from linear mixed effects models of offspring birth traits. Each sub-table gives the main effects and interaction terms for all maternal fitness measures and population density effects remaining in the models after simplification. Results are for models of (a) male offspring birth mass (346 calves born to 131 mothers), (b) female offspring birth mass (328 calves born to 127 mothers), (c) male offspring birth date (346 calves born to 131 mothers) and (d) female offspring birth date (328 calves born to 127 mothers). Both birth mass models (a) and (b) still retain significant main effects of maternal reproductive status, maternal age (quadratic), average March to April temperature and birth date, but these are not shown here for brevity. Similarly, both birth date models (c) and (d) still retain significant main effects of maternal reproductive status, maternal age (quadratic), September to December rain, year and birth mass. All p-values are for a two-tailed test of the null hypothesis that the value of the fixed effect is equal to zero (Crawley 2002).

	value	s.e.	residual d.f.	t-value	p-value
(a) simplified birth mass model (male calves)
no. of adult females	−0.0003	0.0003	206	−1.0143	0.3116
Σpt(i)	−3.6335	2.6294	135	−1.3818	0.1693
no. of adult females: Σpt(i)	0.0388	0.0161	206	2.5075	0.0169
(b) simplified birth mass model (female calves)
no. of adult females	−0.0001	0.0002	196	−0.2609	0.7945
Σpt(i)	2.3016	0.5243	130	4.3903	0.0000
(c) simplified birth date model (male calves)
no. of adult females	0.0000	0.0000	206	0.5148	0.6072
Σpt(i)	−0.4225	0.1484	135	−2.8463	0.0051
(d) Simplified birth date model (female calves)
no. of adult females	0.0001	0.0001	191	0.9675	0.3345
Σpt(i)	−0.1055	0.1624	123	−0.6497	0.5171
age at primiparity (4)	0.0028	0.0053	123	0.5382	0.5914
age at primiparity (5)	0.0173	0.0075	123	2.2997	0.0232