A rapid increase in the number of sika deer (Cervus nippon) in the last decades aroused needs for quantitative estimation of crop herbivory by them, in order to evaluate how much damage they cause to agriculture. Measurement of fecal nitrogen stable isotope ratio (fecal δ¹⁵N) can be a complement to molecular techniques, considering that the application of fertilizer leads to distinctively higher δ¹⁵N values of crops than the adjacent wild plants. For a validation of the method as an indicator of crop consumption, we examined the spatial distribution of the fecal δ¹⁵N, assuming the crop consumption should occur in the individuals of deer inhabiting close to cropland.
Deer feces were collected in 80 forested sites in the northern part of Osaka prefecture. The fecal samples, which were homogenized for each of the fecal mass, were used for δ¹⁵N measurements. Based on GPS telemetry of deer in the region, we assumed that short-time moving range of deer is around 500 m in radius and surrounding land use within the distance from sampling points were used to analyze fecal δ¹⁵N values. Positive correlation between the cropland area and the fecal δ¹⁵N values indicated the availability of crop to deer was a factor of the increase in the fecal δ¹⁵N values.