Sir, Poole (Animal Welfare 1992, 1: 203-220) appears to argue that the welfare of mammals is in some way more important than that of non-mammalian species eg birds, on the grounds that mammals are unique in possessing ‘psychological needs’. We are concerned that an adoption of Poole's basic argument may lead to a ‘two-tier’ approach to the study of vertebrate welfare, where mammals are seen as possessing certain needs that birds do not. We believe any such argument to be flawed and that bird species should be considered no less important when regarding issues of welfare.