The phrase "empty cages" refers to cages that do not have anything or anyone inside them. It represents freedom, release, or the absence of captivity. Full definition
Our shelter is no exception, and in the past rescues have saved hundreds of lives annually by rescuing individual animals and creating empty cages in our shelter. (friendsofbcas.org)
Another trick I have enjoyed over the years involves the occasional empty cage that inevitably happens in the course of a busy day on the floor. (petbusiness.com)
Empty Cages Collective ran this campaign to encourage cat an kitten adoptions and held a special adoption clinic at a pet supply store on Mother's Day. (charitypaws.com)