 While some apparent inbreeding depression was noted in the captive birds, it was certainly lower than might be expected given that the effective population size was maybe 5 individuals during the mid-1970s.It is known that several genetic lineages of Mauritius kestrels have disappeared entirely during the 20th century population decline.However, the debilitating effects of DDT accumulation on the birds' health, and not inbreeding, are considered to have been the major cause for the failure of Temple's breeding program.