Using Placental Scar Counts to Estimate Litter Size and Pregnancy Rate in Lynx

Abstract

We compared post-partum estimates of litter size and pregnancy rate (Mowat et al. 1996) with those estimated from placental scar counts to test the accuracy of the placental scar method. We counted placental scars on uteri taken from lynx (Lynx lynx) carcasses collected from trappers over 3 years of a hare peak and decline in southwest Yukon. We classified scars into ≤ 6 categories based on coloration, though we lumped scars into subjective categories called light, medium and dark for analysis. In utero estimates of litter size were equally close to post-partum litter size when light placental scars were included or excluded. However, pregnancy rate was closest to live birthrate when all scars were included. We recommend researchers classify placental scars after Englund (1970) (or Lindstrom [1981]) with the addition of a seventh category for scars from previous years. We suggest researchers include all scars to estimate pregnancy rate and litter size, except those from previous years. This will increase precision and comparability among studies.