PLACENTAL SCARS AND ESTIMATION OF LITTER SIZE - AN EXPERIMENTAL TEST IN THE ARCTIC FOX

The assumptions required to estimate litter size at birth from counts of placental scars were experimentally tested in the Arctic fox (Alope x lagopus). Effects of abortions were tested by examination of uteri f rom females caused to abort at 20 and 40 days pregnancy. The reliabili ty of estimated litter sizes was tested by comparing litter size at 2- 3 days postpartum with counts of placental scars. Placental scars were categorized according to their visibility, with pale and hardly detec table scars designated as category 1 and dark and fully pigmented scar s as category 6. The results showed that scars from abortions and scar s that persisted for 80 weeks postpartum were paler and less visible t han scars from full-term fetuses at 20-35 weeks postpartum. Pale scars from abortions and scars sustained from earlier pregnancies, therefor e, should be excluded when estimating litter size at birth. Litter siz e at 2-3 days postpartum was not significantly different from estimate d litter size when pale scars were excluded from the estimates. Our re sults confirmed that breeding females might be distinguished from nonb reeders by the visibility of placental scars. The accuracy of this app roach, however, depends on the frequency of late abortions in the popu lation.