Pneumatization of the skull roof and cerebellum region of he occipital bone was studied in 193 skulls of 18 genera and 56 species in the family Parulidae (wood warblers). The grundtypus type of pneumatization, which closes the windows anteriorly in immatures of migratory species, was present in fall migration and was completed on the wintering grounds during December and January. The only genera to show what I call the geospizid type of skull pneumatization were Basileuterus and Phaeothlypis, supporting their treatment as congeners.
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