Study on crow scavenging at garbage stations in Asakura, Kochi City, southern Japan

Abstract

In crowded urban areas, there are various conflicts between Large-billed Crows and Carrion Crows (hereafter referred to as both species of "crows") and humans, the most common of which is scavenging garbage. Some municipalities are changing garbage bags and receptacles to prevent scavenging, but knowledge of the environment and seasons preferred by crows could be helpful to those efforts. Therefore, we performed a study to determine what areas crows prefer to scavenge and where scavenging occurs. The study was conducted in Asakura, Kochi City, with four routes based on distance from the forest and housing type. A total of 122 garbage stations were selected that were always in use on the combustible-garbage collection days that occurred twice per week. The study period was from May to December 2023, with one route patrolled three times every two hours from 6:00 a.m. to 12:00 p.m. per visit. The survey recorded the number of garbage bags (hereafter called "number of bags"), the type of receptacles, and the surrounding environment (housing type, forest coverage, etc.). In the analysis, a generalized additive model was used in which the presence or absence of scavenging was used as the response variable, and the date of the survey, number of bags, type of receptacles, and surrounding environment were used as explanatory variables. Each location was surveyed for 8 to 11 days (36 days total), and scavenging damage was observed at 36 of the 122 locations. The statistical analysis results suggest that in Asakura there is a seasonal change in scavenging, with a high rate of scavenging in the spring season and a subsequent decrease, that measures taken with receptacles have not been very effective, and that crows may prefer areas with a large number of garbage bags when scavenging.