Reduced genetic variation is a severe threat for long-term persistence of endangered animals. Immigration or translocation of new individuals may result in genetic rescue and increase the population viability of the endangered population or species. Unfortunately, studying genetic rescue in wild populations is very difficult, but breeding programs of endangered species can contribute to our knowledge of the diverse effects of genetic rescue.

A recovery breeding program of common hamsters in the Netherlands enabled the study of genetic rescue in an endangered rodent as a few wild hamsters from two nearby and also highly threatened populations were added to the breeding stock.

Litter size increased over the years, but no relation between inbreeding levels and litter size was found. Average litter size benefited from the genetic variation introduced by a hamster from Germany, but hamsters from Belgium had no effect on litter size. Rather than alleviating inbreeding depression the genetic rescue effect observed in this population seems to originate from the introduction of beneficial alleles by the German male. Breeding programs using several populations may increase the success of reintroductions and long-term persistence of these populations.