Table 6. Results from the best-fit (lowest AICc) generalized linear model, with taxonomic group included as a predictor variable, testing the prediction that the advantage of large size in aggressive contests for resources declines with genetic distance among interacting bird species (n = 244 species pairs).

Fixed effects1	Estimate	SE	t	df	P
Intercept2	1.08	0.11	9.70	243,238	<0.0001
Taxonomic group (hummingbirds)	0.05	0.09	0.58	243,238	0.56
Taxonomic group (antbirds/woodcreepers)	0.20	0.09	2.21	243,238	0.028
Difference in mass3	0.85	0.17	4.93	243,238	<0.0001
Genetic distance	0.85	0.49	1.76	243,238	0.08
Difference in mass3×Genetic distance	−2.53	0.84	−3.01	243,238	0.0029

¹ dependent = sqrt{ln[(wins by dominant species+1)/(wins by subordinate species+1)]}.

² intercept value for taxonomic group = vultures.

³ (mass of dominant species−mass of subordinate species)/(average mass of dominant and subordinate species).