Table 1.

Results of the model selection for factors influencing litter sex ratios in North American red squirrels. (All models were run with individual litter sex ratio as the response variable (number of males and females per litter bound as a single object). Fixed and random effects fitted in each model are listed below the model name. Only first-order models are shown. K indicates the number of parameters estimated in each model; Akaike's information criterion adjusted for small sample size (AICc), ΔAICc denotes the difference in AICc values from the top-ranked model; and weight denotes the weight of the focal model among all models presented.)

model	K	AICc	ΔAICc	weight
null ∼ (1 | year) + (1 | dam ID)	3	4383.17	0.00	0.26
grid ∼ + grid + (1 | year) + (1 | dam ID)	4	4383.71	0.53	0.20
spring density ∼ + spring density + (1 | year) + (1 | dam ID)	4	4384.39	1.22	0.14
adult sex ratio ∼ + adult sex ratio + (1 | year) + (1 | dam ID)	4	4384.79	1.62	0.12
food ∼ + cone abundance + (1 | year) + (1 | dam ID)	4	4385.05	1.88	0.10
maternal age (quadratic) ∼ + maternal age2 + (1 | year) + (1 | dam ID)	4	4385.11	1.94	0.10
litter ∼ + parturition date (Z-score) + litter size + grid + (1 | year) + (1 | dam ID)	6	4386.97	3.80	0.04
environment ∼ + spring density + adult sex ratio + cone abundance + (1 | year) + (1 | dam ID)	6	4387.77	4.60	0.03
mother ∼ + maternal age2 + parturition date + cone abundance + (1 | year) + (1 | dam ID)	7	4390.65	7.48	0.01
full model ∼ + adult sex ratio + maternal age2 + spring density + parturition date + litter size + cone abundance + grid + (1 | year) + (1 | dam ID)	10	4394.17	10.99	0.00