My birds will eat paper and cardboard, especially if juice from something prized is dripped on it. I also see Cockatiels sometimes fine chewing clean wood and swallow it. I can't keep potted plants in the room because the tiels and budgies enjoy eating the soil, despite providing mineral block, Manu block and salt spools. It's almost an obsession with them. And Sunny and Oscar, both Poi species, are obsessed with bark peeling and often eat the green cambrian, layer under the dry bark of fresh branches. I have to protect any gypsum board from bird beaks as well. I mounted a large Manu block up in a corner of the room where the birds chewed a hole and the birds crawl up there and chew it constantly,
