Although tropical forest birds are known to prey upon small lizards andfrogs, no study has documented the attributes of vertebrate-eating birds orwhether birds prey opportunistically on the different elements of theherpetofauna within tropical communities. This study is based on a 14-moinvestigation on avian diet, supplemented with a 3-y census of frogs and a1-y census of lizards in a humid forest of central Panama. From 91 birdspecies, 1086 regurgitates were collected, in which were found 75 lizardsand 53 frogs. Over 50% of the common, primarily insectivorous bird speciespreyed upon lizards or frogs, with a mean frequency of 0.26prey/sample. These birds (22 species, nine families) foraged on varioussubstrates from different strata of the forest, fed on invertebratesaveraging from 3.3 to 17.2 mm in length, weighed from 11 to 195 g, and hadbill lengths that varied from 12.2 to 49.8 mm. Based on a logisticregression analysis, intensity of foraging at army-ant swarms was thevariable that best explained the likelihood that a bird species preyed uponlizards, leading to a classification that was 91% correct. In contrast, billlength and body length classified correctly 88% of the frog-eating birds,which showed a fairly constant 1:7 bill length/body length ratio (as opposedto a mean but highly variable 1:10 ratio in other species). A multipleregression analysis showed that seasonal variation in intensity of lizardpredation was positively related to arthropod abundance except during thebreeding season when lizard intake decreased, presumably because nestingbirds did not follow ant swarms. Intensity of frog predation correlated withfrog abundance over time, the latter being inversely related to arthropodavailability. Ninety-seven per cent of all lizards and frogs identified inthe diet samples (n = 105) were from two genera, Anolis andEleutherodactylus, respectively. Prey size distribution in the regurgitatessuggested an optimal prey size of 33.5 mm snout-vent length (SVL) forlizards and 14.5 mm SVL for frogs. Birds preyed opportunistically on thedifferent Anolis species, but almost exclusively upon juvenileindividuals. Abundances of the different Eleutherodactylus speciescorrelated with their predation rates, but these frogs represented only 10%of all the frogs observed during the censuses. The two most common localanurans, Colostethus flotator and Bufo typhonius, were not taken by any birdspecies.