Thick-billed Vireo is primarily insectivorous, but also eats some fruit. Has been seen to eat dragonflies, caterpillars, and Bursera simaruba fruit (personal observation). No detailed diet analyses have yet been published, although one is currently being conducted by the author. There is a correlation in the nitrogen stable isotopes of claws and feathers from individuals on North Andros Island (Bearhop et al. 2003), perhaps indicating that diet is consistent over time within individuals but varies among individuals. However, the paper lacked information about when the samples were collected (i.e. what exact 2-week period during the nonbreeding season), the habitats sampled, and ages of individuals, and so only allows for limited conclusions about this species' ecology.
Thick-billed Vireo forages throughout the available strata, gleaning insects from leaves and branches. Eats prey where captured or flies to another location to consume.
Regurgitates large seeds, such as Bursera simaruba.