Reduced Recruitment in Utah Mule Deer Relative to Winter Condition

Reduced recruitment rates in Utah mule deer (Odocoilus hemionus) showed that significant losses in production were accruing during pregnancy, the neonatal period or during the first few months after birth. The primary objectives of the study were to determine the time, extent and possible causes of these losses. Corpora luteal and fetal rates were estimated by examining the reproductive tracts of 125 carcasses collected on selected herd units in Utah and by observing the reproductive tracts of 136 female deer captured in Spanish Fork Canyon. A laparotomy was performed on each captured female to allow visual examination of the reproductive tract without sacrificing the doe. Live-birth rates were estimated by observing and monitoring pregnant wild does held captive during the fawning period, and by observing free-ranging does tagged with radio-transmitters. Fawn mortality was estimated by monitoring radio-tagged fawns, captured shortly after birth until fawn:doe ratios were observed the following fall. The greatest loss in production occurred during the post-natal period. Annual fawn losses averaged 26.4 percent, while a 3.7 percent interuterine loss occurred before midpregnancy and a 9.5 percent fetal loss was recorded between midpregnancy and parturition. No single mortality factor appeared to be responsible for most of the fawn losses. Condition of the pregnant doe on the winter range was investigated as the cause of reduced recruitment. The condition of the doe had to be accurately estimated while the doe was alive, before the relationship between condition and reproductive success could be evaluated. The condition of 43 carcasses, based upon a modified nutritional status index that included weight corrected for size and age, was highly significantly correlated to condition of the same carcasses estimated by amount of kidney fat (r=0.70, P Weights and sizes of fawns captured shortly after birth were not significantly related to subsequent survival.