HONG KONG — Australian officials have responded to criticism from animal rights activists and celebrities, including the former actress Brigitte Bardot and the singer Morrissey, that a government plan to protect threatened species by killing millions of feral cats is unnecessarily cruel.

Gregory Andrews, Australia’s threatened species commissioner, has written open letters to Ms. Bardot and Morrissey saying that feral cats prey on more than 100 of the country’s threatened species and that they were a “major contributor” to the extinction of at least 27 mammal species in the country over the past 200 years.

Image A feral cat in Australia eating a bird. Credit... C. Potter/Department of the Environment, via Associated Press

He called some of the extinct species, such as the lesser bilby, desert bandicoot, crescent nailtail wallaby and big-eared hopping mouse, “delightful creatures, rich in importance in Australian indigenous culture, and formerly playing important roles in the ecology of our country. We don’t want to lose any more species like these.”