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.