Invasive Raccoons (Procyon lotor) have Little Effect on the Food Habits of Native Raccoon Dogs (Nyctereutes procyonoides) in a Satoyama Area of Tokyo

Abstract

We conducted dietary analysis on 140 raccoon dog fecal samples, collected between March 2019 and February 2020 in a satoyama area in Tokyo, to see if any effects from competition with invasive raccoons were evident. Raccoon dogs mainly consumed fruits, seeds, and cultivated plants (frequency of occurrence 90.7%), earthworms (60.7%), and insects (48.6%). Dominant food types included summer tangerines (Citrus natsudaidai), and berries (e.g., Vaccinium spp.), with earthworms (Oligochaeta spp.) providing their primary source of protein. These raccoon dogs consumed more fruits but less insects than reported by other studies from Japan. We then compared our results with a previous study (2004)(2005) in the same area, prior to the arrival of invasive raccoons. We detected minimal effects of raccoon arrival on raccoon dog summer or autumn diet, thus allowing raccoon dogs to find sufficient food to accumulate body-fat for over-wintering; however, their restricted winter diet diversity, with fewer animal species consumed, suggests that they may experience some protein limitation prior to the cub rearing season. The co-existence of raccoon dogs alongside invasive raccoons currently appears viable in this satoyama area, apparently enabled by the ability of raccoon dogs to shift their diet to include more fruit.