Comparison of feeding habits and habitat use between invasive raccoons and native raccoon dogs in Hokkaido, Japan

Abstract

Background In Japan, invasive raccoons cause severe ecological and social problems by transmitting pathogens to humans, livestock, and native species, causing substantial crop damage, and competing with native species. Possible competition between invasive raccoons and native raccoon dogs is of concern in Japan because Japanese raccoon dogs have a limited distribution and are native only to Japan and the two species have similar characteristics. We assessed potential competition between raccoons and raccoon dogs by comparing feeding habits and habitat use. Results Both species were captured in Hokkaido, Japan from 2004 to 2017. More raccoons were captured close to agricultural land at the forest periphery (70.1%, 358/511); conversely, more raccoon dogs were captured in the forest core (74.9%, 253/338). Feeding habits were then examined by fecal analysis and stable isotope analyses. Fecal analysis revealed both species to be opportunistic omnivores that consumed easily found food items. However, raccoon feces contained more crops, whereas raccoon dog feces contained more insects, reflecting the different locations in which the species were trapped. Moreover, stable isotope ratios were significantly higher in raccoons than raccoon dogs (Corn has the highest carbon stable isotope (δ13C) value, and amphibians and reptiles are high in nitrogen stable isotope (δ15N); forest resources such as insects and wild fruits are low in δ13C and δ15N). Conclusions We conclude that both species ate similar food types, but their food preferences appeared to differ. Raccoon and raccoon dog habitat use also differed, possibly because the two species inhabited areas where they could easily obtain their preferred foods. Therefore, the current feeding habits and habitat use of raccoons do not appear to overlap sufficiently with those of raccoon dogs to impact the latter. The results of this study, particularly the stable isotope data, may provide a useful precedent for future studies of competition in medium-sized mammals, particularly canids.

Predation impacts of invasive raccoons on rare native species

“…Hori et al 15 successfully observed raccoons preying on Hokkaido brown frog by camera trap survey in spring. Frog bones were detected in multiple individuals in our previous study 23 . Therefore, frog bones can sometimes be detected in the faeces or stomach contents of raccoons.…”

“…The main animal food resources were birds (9.66%), reptiles (9.35%), rodents (9.18%), and amphibians (9.15%). In our previous study on the diet of raccoons in Nopporo Forest Park from spring to summer, a faecal analysis showed that plant material food resources, such as herbaceous plants, crops and wild fruits, accounted for about 80% of total consumed food; vertebrates, such as amphibians, accounted for less than 2% 23 . The results of this study contradicted those of the conventional method, faecal analysis, because it www.nature.com/scientificreports/ is difficult to confirm the presence of easily digested animal food resources, such as amphibians and reptiles, in stomach contents and faeces 24 .…”

“…In addition, because we added measurements of δ 34 S, the accuracy of discrimination between food resources was improved, and we could estimate the feeding habits of raccoons more precisely. The conventional method of measuring only δ 13 C and δ 15 N can distinguish between forest resources and agricultural-based food resources such as corn and livestock forage crops 23 . However, food resources with similar δ 13 C and δ 15 N values, such as amphibians, reptiles, birds, rodents, and crustaceans, are more difficult to distinguish.…”

“…1 ). Trapping points within 250 m of the forest boundary line facing the farmland were defined as ‘around the farmland’ (31 points), and other points were defined as ‘in the forest’ (55 points) using QGIS version 3.10 23 . Captured raccoons were anesthetised with butorphanol tartrate (Vetorphale 5 mg, 1.2 mg/kg; Meiji Seika, Tokyo, Japan), medetomidine hydrochloride (Dolbene, 40 µg/kg; Kyoritsu, Tokyo, Japan), and midazolam (Dormicum injection 10 mg, 0.2 mg/kg; Astellas, Tokyo, Japan) by intramuscular injection and euthanised by potassium chloride injection into the heart.…”

Do alien predators pose a particular risk to duck nests in Northern Europe? Results from an artificial nest experiment

“…However, because of its rapid population growth rate and range expansion in central Europe, we can also expect this population to develop rapidly in Denmark (Salgado 2018). Raccoon and raccoon dog are known opportunistic omnivores, but in Japan their habitats overlap little, as raccoon dogs (native) are more common in forested landscape and raccoons (alien) in agricultural land: competition between these two species is low (Osaki et al 2019). Further expansion of the current distribution of the raccoon in northern Europe would enlarge the potential of alien predators to function as major duck nest predators.…”