Selection of diet by metamorphic and juvenile western toads (Bufo boreas) in northeastern Oregon

The decline of Bufo boreas, the Western Toad, in portions of its range has accentuated the need for more complete information on all life stages of this species. Our objectives were to describe the diet of recently metamorphosed and juvenile (one-year old) B. boreas and then compare it to the available arthropods. Metamorphs (n = 200) and juveniles (n = 176) preyed on small arthropods ( 20 families within 10 orders of insects, two orders of arachnids, and a few gastropods. The majority of the numbers of prey taken by metamorphs consisted of adult Hemiptera (24%), adult Hymenoptera (19%), and Arachnida (11%). Juveniles primarily fed on Collembola (48%), Hymenoptera (20%) and Coleoptera (11 %). We found that the biomass of the diet sample was correlated with the mass of the toad. Metamorphs and juveniles selected prey in a nonrandom manner. Metamorphs fed on a higher proportion of Hemiptera (specifically Aphididae), Hymenoptera (specifically Formlcldae), Lepidoptera, Coleoptera, and Arachnida and on a lower proportion of Diptera compared with available arthropods. Juveniles fed on a higher proportion of Hymenoptera (specifically Formicidae), Coleoptera, Diptera, and Arachnida, but on a lower proportion of Collembola compared to available arthropods.