Harare - Poachers in Zimbabwe are targeting small rhino for their horns, a ranger said on Monday.Two rhino calves were among the five black rhino killed by poachers in the south of the wildlife conservation region Save Valley Conservancy last year, Bryce Clemence of Anti-Poaching and Tracking Specialists (ATS) told Sapa.The two calves were siblings. One was around 9 months old, the other about 3 years old, Clemence said.Both were males, the offspring of a female rhino known to locals as "Diana"."[The poachers] shot her calf... Diana ran off with the other calf.""They found her with the little one, opened fire on both, and killed the little one," he said.The poachers then cut the horn off the calf."His horn was about 40g, there was hardly anything," Clemence said.The fact that the poachers took it showed just how much it was worth in the illegal international rhino horn market.Rangers found where the calves had been killed and tracked the wounded mother. A veterinarian was brought in to treat Diana's wounds."She made quite a quick recovery," said Clemence.But then her condition began to deteriorate.Seven months after the February attack that killed her babies, Diana too died. It was later found that she died of a bone marrow infection in her leg.This was traced to one of the bullets lodged in her leg."She was a beautiful rhino," Clemence said.Clemence, his wife Lara, and his team of trained rangers have been operating in the private Save Valley Conservancy since April 2012.While losses like that of Diana and her babies were real setbacks, Clemence said there was cause for hope.Drop in rhino deathsThe number of rhino losses had declined. In the four months before Clemence began working in the Save Valley, there were 14 rhino losses."At one point 10 rhino were lost in 10 weeks," he said.He and his men's job involved a considerable amount of danger as they tracked and tried to apprehend armed poachers."Our value is in our men," he said. "We train them to very high standards.""We are driven by the same drive - we don't want to see the rhino extinct."There are fewer than 500 black rhino left in Zimbabwe.Many of the black and white rhino left are guarded round the clock in intensive protection zones, such as in the Kyle Recreational Park in southern Zimbabwe and the Matobo National Park near Bulawayo.Last year, Environment Minister Saviour Kasukuwere said the number of rhino killed by poachers across Zimbabwe was on the decline. It was down from 52 in 2010 to 16 in 2013."We are very optimistic," said Clemence. "This is a complete life dedication."