Arthropods are important prey for most forest birds in Hawaii. The relative abundance of arthropods on koa (Acacia koa) changed significantly during an outbreak of the koa moth (Scotorythra paludicola) that occurred across much of Hawaii Island during 2013-2014. The outbreak resulted in large tracts of koa forest becoming defoliated by large numbers of koa moth caterpillars. This data release includes metadata and tabular data that documents how bird diets changed at Hakalau Forest National Wildlife Refuge during the outbreak. The data set documents numbers of koa moth caterpillars and other arthropod prey consumed by forest birds prior to, and during the koa moth outbreak. Diets were reconstructed by identifying arthropod body parts from bird fecal samples collected during mist-netting operations conducted at two study sites dominated by koa.