RENO, Nev. - Activists are questioning the rising death toll from a controversial government roundup of wild horses from the range north of Reno.

U.S. Bureau of Land Management spokeswoman JoLynn Worley said 77 mustangs involved in the Calico Mountains Complex gather have died so far - 70 at a Fallon facility where they were taken and the rest at the roundup site.

That's nearly double the 39 horses that had died when the roundup of 1,922 horses concluded on Feb. 5.

Leaders of the horse advocacy group Cloud Foundation based in Colorado Springs, Colo., are pressing the government for measures to deal with the situation.

"Something has gone way wrong here," said group spokeswoman Makendra Silverman. "Somehow these horses aren't transitioning well. It seems to us it's because they put them through a horrific roundup in the winter," when wild animals have lower reserves of fat.

Worley attributed the deaths mostly to the poor body condition of mares that were sent to Fallon, where the animals are being prepared for adoption or transfer to pastures in the Midwest.

Many mares also are having difficulty making the transition to a diet of hay in Fallon, Worley said. Forty-eight of the 70 deaths in Fallon involved mares, she said, and the number of deaths varies from roundup to roundup.

The BLM has not regularly reported to the public the number of horses killed in the course of roundups.

Silverman questioned whether the quality of hay might have something to do with the deaths, and noted about 40 pregnant mares also have had miscarriages.

Worley said her agency tries to provide the best feed available, and a veterinarian is available to care for the animals.

Some of the mares showed up dead at Fallon, while others were euthanized there, she added.

The BLM maintains that the roundup was necessary because an overpopulation of horses is harming native wildlife and the range itself, and threatening the mustangs with starvation. Activists unsuccessfully sued to halt the roundup, branding it as unnecessary and inhumane.