Border fences aimed at keeping smugglers and illegal immigrants out are contributing to dramatic declines in the numbers of pronghorn antelope that would otherwise roam between Arizona and Mexico, environmentalists say.

Arizona Game and Fish surveys reported 122 pronghorns in two border-area herds in 2005 but just 26 in a 2012 survey, according to the Arizona Republic.

The department plans to capture pronghorns in Chino Valley north of Prescott in north-central Arizona to add them to border-area herds in Southern Arizona.

Environmentalists say that might not work because border fences still would restrict the pronghorns' movement.