Winter fawn survival in black-tailed deer populations affected by hair loss syndrome.

Abstract

Overwinter fawn mortality associated with hair loss syndrome (HLS) is anecdotally thought to be important in declines of Columbian black-tailed deer (Odocoileus hemionus columbianus) populations in Washington and Oregon (USA). We determined prevalence of HLS in black-tailed deer, September and April fawn:doe ratios, and minimum overwinter survival rates of fawns for selected game management units (GMUs) in western Washington from 1999 to 2001. Prevalence of HLS ranged from 6% to 74% in fawns and 4% to 33% in does. Minimum fawn survival ranged from 0.56 to 0.83 and was unrelated to prevalence of HLS in either does (r=0.005, P=0.991) or fawns (r=-0.215, P=0.608). The prevalence of HLS in either does or fawns was also unrelated to either fall fawn:doe ratios (HLS does: r=-0.132, P=0.779; HLS fawns: r=0.130, P=0.760) or spring fawn:doe ratios (HLS does: r=-0.173, P=0.711; HLS fawns: r=-0.020, P=0.963). However, the prevalence of HLS in does and fawns was strongly related (r=0.942, P=0.002), and GMUs with high prevalence of HLS had lower deer population densities (fawns: r=-0.752, P=0.031; does: r=-0.813, P=0.026). Increased overwinter mortality of fawns because of HLS was not supported by our data. Decreased production of fawns, increased summer mortality of fawns, or both were seen in six of eight study GMU-year combinations. Observed rates of productivity and minimum fawn survival were inadequate to maintain population size in five of eight study GMU-year combinations, assuming an annual doe survival rate of 0.75. The influence of deer condition and population health on adult survival, fawn production, preweaning fawn survival, parasitism, and prevalence of HLS in both fawns and adults need to be clarified to identify what factors are limiting black-tailed deer productivity.