THE USE OF FLUORESCENT PIGMENTS TO ESTABLISH MOTHER-OFFSPRING RELATIONSHIPS IN SMALL MAMMALS

We present results suggesting that brushing nursing mothers with fluor escent pigments improves the success of establishing mother-offspring relationships, compared with the use of capture data alone. The markin g frequency of juveniles averaged 63%, but varied considerably among s even root vole (Microtus oeconomus) populations, presumably according to the amount of pigment applied during brushing of mothers. Based on location of first capture and body weight relative to putative mothers delivery dates, and home range areas of mothers (estimated from captu re data), 69% of the juveniles could be assigned to one specific mothe r. The remaining 31% had more than one potential mother. For marked ju veniles for which trapping data suggested only one mother, the corresp ondence with maternity assignment from fluorescent pigment staining wa s 99%. The frequency of contamination was low and we therefore recomme nd that future studies should use large quantities of pigment during b rushing, and repeated brushing as long as females are nursing (lactati ng). High trappability of juveniles is required for good results with fluorescent pigments because the pigment transferred from nursing moth ers is no longer apparent on most juveniles after the age of 24 days. We also report a new application of the fluorescent powder technique f or establishing whether apparently lactating females actually are nurs ing young.