Harare - The manager of a conservancy in southern Zimbabwe says lions there recently killed two endangered black rhino calves - and the fear is that still more may fall victim.Blondie Leathem of Bubye Valley Conservancy told News24 that two carcasses were found in the 3 000km-squared conservancy during a dehorning exercise last month.The unusual predation - lions rarely prey on rhino although it is not unheard of - may be a result of an over-population of lions in this highly-successful reserve.Bubye Valley Conservancy was in the news earlier this year when officials there said that a cull of up to 200 lions there was "not yet necessary".Both calves were about four months old, Leathem said.He said: "The carcasses were found when we were busy with a combined calf ear-notching and rhino de-horning exercise in August.""There are probably more that we do not know about," he added.Higher rate of reproduction As in the rest of southern Africa, Zimbabwe's rhino population is already under threat from poachers. Last year rhino poaching fatalities countrywide were particularly serious, with around 50 killed. There are around 700 black and white rhinos in Zimbabwe.The hope is that rhinos breeding will at least mitigate some of the losses to poaching. But in ideal conditions a female rhino can only produce a calf every 30-36 months, Leathem says. Lions have a much higher rate of reproduction.Bubye has more than 500 lions. The population has grown from just 24 lions just eighteen years ago, a clear indication, Leathem says,"of just how lion can recover and reproduce if given space, adequate protection from humans and abundant prey species."Efforts are being made to see if some of the conservancy's lions can be translocated. Rwanda, Malawi and Zambia have all been mentioned as possible destinations. Lions are very difficult to move into areas that already have lions.Says Leathem: "There are no definite takers for lions yet but we are still hoping that there might be some suitable areas that will want [lions] next year."Zimbabwe's lion population has been in the spotlight since the killing of Cecil the Lion just outside Hwange National Park last year.