An evaluation of a weaning index for wild fishers (Pekania [Martes] pennanti) in California

Abstract Conservation concern for fishers (Pekania [Martes] pennanti) in the Pacific stateshas highlighted a need to develop cost-effective methods of monitoring reproductionin extant and reintroduced fisher populations. We evaluated the efficacy of nipple size as a predictive index of weaning success for females with known reproductivehistories from 3 study areas in California. We captured and radiocollared 91 female fishers on 146 occasions between 2004 and 2011 and measured the width and height of all 4 nipples and quantified reproductivestatus via radiotelemetry. We classified each radiomarked female into 1 of 3 reproductiveclasses (nonbreeders, attempted breeders, and current breeders) based on our telemetry observations during the den season prior to capture. We used a modified random forests (RF) procedure to account for repeated measures of individual females sampled in multiple years. Our modified RF procedure correctly classified reproductiveclass for 130 (89%) and 131 (90%) of our 146 obs...