While this controls the amount of carbon dioxide they're absorbing, it has the added outcome of limiting the amount of water released into the air from plants. (sciencebuzz.org)
You can also use the counting trick for limiting the amount of time they stay on the breast. (themilkmeg.com)
To protect these values, only limited amounts of people at a time are allowed to visit the area and a special permit is required. (kakadutourism.com)