Table 1. Phylogenetic generalized least squares models testing association among geographic species ranges in birds and genome size, chromosome number, body mass, relative brain mass and latitude.

Three models differed by available sample size for each explanatory variable. Statistically significant effects have emboldened P-values.

Model 1st (N = 637 species)
Effect	estimate	SE	t	P
(Intercept)	2947223.7	13563675.8	0.217	0.828
Genome size	11347387.5	3810612.2	2.978	0.003
Body mass	−1666844.5	792465.3	−2.103	0.036
Geographic latitude	107082.4	34917.7	3.067	0.002
Model 2nd (N = 311)
Effect	estimate	SE	T	P
(Intercept)	1282122.5	17644249.3	0.073	0.942
Genome size	16502711.4	5846290.2	2.823	0.005
Body mass	−2265842.6	1127589.4	−2.009	0.045
Brain mass (residual)	−1224487.9	5200002.4	−0.235	0.814
Geographic latitude	27604.6	57284.6	0.4882	0.630
Model 3rd (N = 65)
Effect	estimate	SE	T	P
(Intercept)	25833067.5	31459858.8	0.821	0.415
Genome size	29848628.7	11134362.6	2.681	0.009
Chromosome number	−345377.8	276973.9	−1.247	0.217
Body mass	−3923399.6	1685932.1	−2.327	0.023
Brain mass (residual)	264551.6	8961357.9	0.030	0.976
Geographic latitude	25833067.5	31459858.8	0.821	0.415