Temporal and spatial variation in the risk of grazing damage to sown grasslands by sika deer (Cervus nippon) in a mountainous area, central Japan

Abstract

Grazing damage to pasture plants by cervids results in economic losses and substantially increases production costs for dairy farms. Understanding both temporal and spatial variations in the risk of grazing damage to sown grasslands by deer will help in deciding suitable timing for culling and in prioritizing pastures and meadows for the introduction of damage prevention management, such as fencing and culling. Here, we assessed both the season and the sown grassland characteristics that attracted more sika deer (Cervus nippon) on a dairy farm located in a mountainous area of Gunma Prefecture in central Japan. We conducted spotlight counts on the farm during 2012–2015 to record the number of deer in 32 management units utilized as pastures or meadows. Deer utilized the grasslands year-round, but their numbers fluctuated seasonally. Deer utilization was the highest in November and the lowest in February. During the snow-free season (April–November), there were more deer in fertilized management units but fewer in cattle-stocked management units. During the snow season (December–March), more deer were found in management units with steeper terrain. Factors affecting deer utilization differed by season: the quality and availability of pasture plants were the primary drivers of deer utilization in the snow-free season, but only the availability of pasture plants drove utilization in the snow season. Farm managers should consider damage control plans for deer based on the risk of grazing damage, which fluctuates depending on both the season and the characteristics of management units.