Table 2. Model selection and LM to test the influence of mean parental age, sex of the offspring and the year of sampling and their interactions on offspring body condition.

The best model (in bold type) was selected by using a backwards stepwise approach starting from the most global model (models were simplified by eliminating independent variables with p ≥ 0·10). Parameter estimates are provided for the best model.

Variable of interest	Explanatory variables	df	F-value	p-value
Offspring body condition	Mean parental age	1.47	18.8	<0.001
	Sex of the offspring	1.47	12.6	<0.001
	Year of sampling	2.45	1.47	0.241
	Mean parental age x sex	1.47	10.5	0.002
	Mean parental age x year of sampling	2.41	0.038	0.963
	Sex x year of sampling	2.43	1.82	0.173
Parameter	Estimate	Standard error	t-value	p-value
Intercept	2013.3	408.4	4.93	<0.001
Mean parental age	113.3	26.1	4.34	<0.001
Sex of the offspring	1852.4	522.2	3.55	<0.001
Mean parental age x sex	-104.1	32.1	-3.24	0.002