Annual variation in recruitment rates for the sika deer (Cervus nippon) population in eastern Hokkaido, Japan

To understand wildlife population dynamics, it is crucial to determine the factors influencing annual variations in recruitment rates. Over a 12-year period (1995-2007), we conducted herd count surveys in Akan-Mashu National Park, eastern Hokkaido, Japan, to investigate the recruitment rate of the sika deer (Cervus nippon) population. The observed trend revealed a decline in fawn-female ratio (number of fawns per 100 females) from January to April each year. Furthermore, there was significant annual variation in recruitment rates (fawn-female ratio in April). We analyzed the effects of relative density of sika deer, snow water equivalent (SWE), wind speed (WIND), and survey date on the number of females with or without a fawn using generalized linear mixed models. The selected model, including SWE, WIND, and survey date, highlighted SWE and WIND as strong determinants of recruitment rate. Conversely, the relative density index had no influence on recruitment rate. We hypothesize that the reduced availability of food resources and winter weather severity, due to snow cover and wind chill, led to fawn malnutrition and increased winter mortality.