The association between morphological and ecological characters across a global passerine radiation

Strong relationships between morphological and ecological characters are commonly predicted to reflect the association between form and function, with this hypothesis being well supported in restricted taxonomic and geographic contexts. Conversely, among broader sets of species, ecological variables have been shown to have limited power to explain morphological variation.   
To understand these apparent discrepancies, for a large and globally distributed passerine radiation we test (i) whether the character states of four ecological variables (foraging mode, diet, strata and habitat) have different morphological optima, (ii) whether ecological variables explain substantial variance in morphology, and (iii) whether ecological character states can be accurately predicted from morphology.
We collected ten linear morphological measurements for 782 species of corvoid passerines, and assessed (i) the fit of models of continuous trait evolution with different morphological optima for ea...