Are Amphibian Eggs a Precious Food Resource for Cynops pyrrhogaster (Amphibia: Urodela) in Spring?

Most true predators are generalists, and it is difficult to examine their actual diets in the wild. In many cases, the prey that experience a large impact are also not well known. Amphibians are generalist predators that prey mainly on insects, and amphibian species active beginning in spring are considered to prey on food resources other than insects in this season due to the low number of insects. The Japanese red-bellied newt (Cynops pyrrhogaster) is a generalist predator widely distributed in Japan and is known to frequently prey on amphibian eggs. Here, we showed that amphibian eggs are a precious food resource for C. pyrrhogaster in spring. The total weights of stomach contents were compared among seasons and we found that the total weights of stomach contents in spring were the same as those in summer. Also, we examined whether C. pyrrhogaster preys on amphibian eggs instead of insects in spring. The composition of the taxonomic groups in their stomach contents was compared among the seasons, and the indicator groups in their stomach contents were identified in each season. We found that they preyed not only upon insects but also upon amphibian eggs in spring, while they preyed mainly upon insects in summer and autumn. Our results suggest that C. pyrrhogaster preys on amphibian eggs to compensate for the shortage of food in spring when the number of insects is low.