We studied a population of Ameerega flavopicta on an island in southeastern Brazil that was formed during the filling of a reservoir in 1965. We studied frog condition factor, diet composition (through induced regurgitation), prey preferences (based on prey availability assessed at frogs' habitats), vocalizations, breeding period, and density. We conducted fieldwork monthly from July 2008 to March 2010 to locate frogs in marked grids. We photographed individual frogs to register particular patterns of dots on the dorsum that allowed individual recognition. During the rainy season A. flavopicta used a temporary trench inside the inland vegetation (Cerradão) for tadpole development. The frogs migrated to the margins of the reservoir during the dry season, when the trench dried completely. Frogs measured 24.0 ± 4.0 mm (snout–vent length), and mass was 1.6 ± 0.5 g (N = 47). Their condition varied among months but not between the two areas used (trench surroundings inland and island shores). Ameerega flavopicta favored specific food items and preferred Lepidoptera larvae in both areas. The advertisement call was composed of simple notes repeated 102.7 ± 7.63 times per min, lasting 166 ± 42 msec and spaced by 387 ± 66 msec. The breeding period differed from that reported for other areas. This and other aspects of the Pirapitinga population differed from populations studied elsewhere. Differences may be attributable to a bottleneck effect or different selective pressures in this isolated population.