JOHANNESBURG (AP) — Poachers have killed record numbers of rhinos in South Africa in recent years, but some conservationists believe the toll could be higher than the official figures.

Allison Thomson, founder of a group called Outraged SA Citizens Against Poaching, said there are cases not included in the official statistics. For example, lions or other predators probably kill some vulnerable rhino calves whose mothers are poached, Thomson said.

South Africa’s environment ministry, which reported 1,215 rhino poachings last year, said Wednesday that aerial surveillance and other “concerted efforts” are made to detect carcasses of rhinos killed by poachers. Home to most of the world’s rhinos, South Africa has struggled to contain poaching syndicates because of rising demand for their horns in parts of Asia, including Vietnam.

The count includes poached rhinos “irrespective of the age of the animal or whether the horns have been removed or are still intact,” the ministry said in a statement emailed to The Associated Press.

The ministry said it is unlikely that some rhino poachings are not reported “as may have happened in the past on one or two occasions.”

The dead fetus of a pregnant rhino killed by poachers would be included in poaching statistics, but “some” may be missed if scavenging animals reach the carcass before investigators, the ministry said.

The anti-poaching group has reported a toll of 710 so far this year, based on media reports and other sources.

Environment Minister Edna Molewa has released figures through the end of April — a toll of 393 rhino poachings, an increase of about 20 percent over the same period in 2014.

Most owners of rhinos in private reserves have insured them because of increased poaching, and they would have to report a rhino killing in order to receive compensation, the ministry said.