Habitat-Associated Dietary Plasticity in the Japanese Weasel (<i>Mustela itatsi</i>): Fecal Analysis in a Floodplain Wetland and Comparative Synthesis

Journal article

The range of food resources consumed by opportunistic carnivores is shaped by habitat-specific availability and productivity. However, baseline data on the diet of the Japanese weasel (Mustela itatsi) in managed wetland habitats remain scarce. Firstly, we conducted a diet study examining Japanese weasel scats from the Watarase-yusuichi wetland (WYW) (September 2024-August 2025). Based on 103 fecal samples, we calculated seasonal frequency of occurrence (FO) for 16 food categories and estimated their relative volume (RV) using the point-frame method. Surprisingly, plant material and fruit seeds were eaten frequently across seasons, and fruit seeds constituted a major component of scat volume, particularly in summer. Secondly, we compared baseline WYW data with published datasets from two contrasting aquatic habitats (a suburban river area and a rice paddy landscape) using harmonized categories and multivariate analyses. Diet composition differed markedly among study sites, and the PERMANOVA analysis indicated a significant effect of sampling site (R2 = 0.643, p = 0.001) with a weaker seasonal effect (R2 = 0.208, p = 0.038), with no significant pairwise differences between seasons (all p ≥ 0.300). Although cross-site comparisons should be interpreted cautiously because datasets were collected in different decades (1998, 2018, and 2024-2025), these findings support habitat-associated trophic plasticity in the Japanese weasel, with dietary shifts across habitats and seasons apparently reflecting variation in available food resources. In managed floodplain wetlands such as WYW, maintaining a mosaic of reed beds, ponds, and channels may help sustain dietary flexibility and population persistence in this species.

Authors: Qiao, S; Suzuki, K; Yoshikawa, M; Newman, C; Kaneko, Y

• Publication status: Published
• Peer review status: Peer reviewed
• Publisher: MDPI
• Journal: Animals
• Volume: 16
• Issue: 11
• Pages: 1720
• Publication date: 2026-06-04
• DOI: 10.3390/ani16111720
• EISSN: 2076-2615
• ISSN: 2076-2615
• Pmid: 42278150
• Language: English
• Keywords: Japanese Weasel; Dietary composition; Scat Analysis; Trophic Plasticity; Wetland Habitat