Complex sentence: Budgerigars and other smaller birds may choose to pick at cockatiels' feet causing amputated toes, whilst Lovebirds and Parrotlets should never be free and/or unsupervised around Cockatiels as sooner or later they may cause them serious or fatal injuries.
Split into simpler sentences: Budgerigars and other smaller birds may choose to pick at cockatiels' feet causing amputated toes. While Lovebirds and Parrotlets should never be free and/or unsupervised around Cockatiels as sooner or later they may cause them serious or fatal injuries.