Mangrove Cuckoo appears to consume a wide range of animal matter, probably reflecting the diverse habitats occupied by this species. Grasshoppers (Orthoptera: Locustidae) made up the majority of prey items recovered from the stomachs of 15 birds collected in Puerto Rico (Wetmore 1916b). Lepidopteran larvae were the second most common prey item, including, based on the spines embedded in the stomach lining, at least some Arctiidae caterpillars. Stomach contents examined in other areas (e.g., Florida; Howell ) have also been lined with the spines of these hairy caterpillars, leading some to suggest a predilection for the larvae of Arctiid moths (e.g., Hughes 2010, Wetmore 1916b). Other arthropod prey items reported by Wetmore (1916b) included crickets, walking sticks (Phasmatodea), earwigs (Dermaptera), cicadas (Cicadidae), beetles (Coleoptera), and spiders (Araneae). A single snail (Subulina sp.) was also recovered (see also Bowdish ).
In addition to eating large invertebrate prey, Mangrove Cuckoos also preys upon and consume small vertebrates. Anolis lizards made up a large part of the diet of Mangrove Cuckoos on Grenada, especially during the dry season (Wunderle 1981). Predation on Anolis lizards has also been reported from Costa Rica (Stiles and Skutch 1989) and Puerto Rico (Bowdish 1902). Pérez-Rivera (1997) observed Mangrove Cuckoos feeding on Eleutherodactylus frogs in Puerto Rico; Robertson (1978) also reported collecting a Mangrove Cuckoo in Florida that had consumed a hylid treefrog. Reported to prey upon the eggs and nestlings of other birds (see Social and Interspecific Behavior), but no evidence of the extent to which this behavior may occur.