Phylogenetic generalized linear models assessing exogenous correlates among extents of molts and dichromatism
For individual pairwise comparisons between variables, we found that extent of seasonal dichromatism was best predicted by extent of prealternate molt (adjusted R2= .312, p<.001), and day length (adjusted R2= .065, p=.046), and migration distance (adjusted R2= .072, p =.039) which were correlated with prealternate molt. Seasonal dichromatism was also significantly correlated to foraging stratum (adjusted R2= .078, p=.032), which was not correlated with prealternate molt. The extent of prealternate molt was significantly correlate with extent of seasonal dichromatism (adjusted R2= .312, p<.001), day length (adjusted R2= .16, p = .001), migration distance (adjusted R2= .188, p = .013), and breeding latitude (adjusted R2= .109, p = .013); figure 1).
16 mixed models significantly predicted the extent of prealternate molt with significance of p<.05, and we ranked these models using the sample size-adjusted information theory criterion AICc(Table 1). The top model for extent of prealternate molt outperformed all other models by a sizable margin, and the top two models combined accounted for the majority of the AIC weight. Top models that predicted the extent of prealternate molt generally included day length, solar radiation both in the breeding and nonbreeding season, and migratory distance as predictor variables. In all, we found fifteen models that predicted the extent of seasonal dichromatism with significance of p<.05; and these models included the extent of prealternate molt, foraging stratum both in the breeding and nonbreeding season, and migratory distance (Table 1). Top models were evaluating seasonal dichromatism more evenly weighted than models for prealternate molt, with the top two models produced similar AICcvalues, and the third and fourth models produced similar AICc values. All four of these top models, which accounted for the majority of the AICc weight, included extent of prealternate molt and foraging stratum. Foraging stratum, both in the breeding and nonbreeding season, was the main predictor variable in the top models for the extent of seasonal dichromatism that was not associated with top models of prealternate molt.