What type of garbage containers do crows attack?

Abstract

Crows Corvus macrorhynchos & C. corone foraging on garbage that has been placed on public streets for collection is a hygiene issue for communities in many areas of Japan. In Hakodate City, we conducted a study to identify factors affecting the frequency of damage to garbage bags by crows. Typically, citizens select their own type of container to hold plastic garbage bags while on the street awaiting garbage collection. Crows often pull the plastic bags out from the containers, or peck through gaps in the containers to create holes in the plastic bags, which results in garbage scattered on the road. To answer the following three questions, we collected data on this process: (1) Is there a seasonal difference in the frequency of crows foraging on garbage bags, or a seasonal variation in foraging on specific types of containers? (2) Is there a temporal difference in the probability of crows damaging garbage bags? (3) Of the most common types of metal enclosure for garbage bags used in Hakodate City, which is the most vulnerable to the crows’ attack? We studied 2,000 garbage bags during the summer and the winter of 2016. The results were that (1) garbage bags were damaged more in the wintering season than in the breeding season, (2) garbage bags put out in the early morning were damaged more frequently than those put out late in the morning, and (3) garbage bags in the metal mesh enclosures with the larger mesh size, and with a greater number of inner surfaces in direct contact with garbage bags, were damaged more frequently by crows. These results can help us design garbage containers that provide additional protection from foraging crows, and reduce the resulting unhygienic mess on public streets.