Nine pygmy rabbits died at Northwest Trek near Eatonville during the past month as an unexplained disease swept through the endangered population.
Trek officials said the deaths constituted about half of the stock, which was being bred and reared in captivity for eventual release into the wild.
The cause of the rabbits' deaths is unknown, but "the situation is being handled as a highly contagious, acutely lethal disease," according to a news release.