Ants can be a problem in many places in the world... In the summer when it's hot here, it really brings them out from their underground nests and into people's homes.
Here, there is a natural insect killing product that is made of concentrated citrus oil (from oranges). It's called Orange Guard, but it's from a small manufacturer and I doubt it's distributed worldwide. It's very toxic to insects, and kills them right away (just killed a fly with it tonight in fact), yet completely safe for birds and mammals. Leaves a pleasant orange scent behind. I bet you can make your own concoction from citrus peels. Crushed or mashed, or however you need to do it to get the oils out, and rub it on the legs of the cage or on the areas of the home where you might see the ants are coming in from. I've never tried the water, but I bet it would work! Good luck.