Diet and prey availability of Columbia spotted frogs in northeastern Oregon
Bull, Evelyn L.
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Baseline information on the diet and prey availability of Columbia spotted frogs is lacking from most of the species range. Diet was determined from June through October 2002 for 296 frogs in northeastern Oregon. Number of prey items, diet composition, and biomass indices were compared by sex, size classes, water type (ponds versus rivers), month, and study site. Available invertebrates were determined from sticky traps and dip netting in ponds and rivers. A total of 1,299 prey items were identified with an average of 4.4 prey items in each sample (range=0-28). A wide variety of prey were identified including 33 families from 20 orders of invertebrates with only 3 orders representing gtoreq10% of the composition: beetles (21%), ants/wasps (21%), and flies (10%). Only 14% of the prey were in the larval stages. Female frogs ate about 60% more biomass than males of the same size, presumably because of their need to produce eggs. Biomass of male frog diet samples were greater in rivers than in ponds with a higher percentage of stoneflies, water striders, and beetles. Frogs actively foraged all summer with the highest biomass in September and the lowest in July. Over the summer, composition of spiders, beetles, and flies decreased, while true bugs and ants/wasps increased in the diet. Among study sites, ants/wasps were most abundant at the higher elevations. A higher proportion of invertebrates occurred in the larger sizes in the diet compared with samples of available invertebrates