The Nature and Evolution of Behavioural Needs in Mammals
Abstract:Mammals are unique among vertebrates in experiencing a need to carry out behaviours which are not necessary for their immediate survival This poses questions as to the nature of these behavioural needs, how they evolved and their implications for the welfare of mammals in captivity. Evidence is provided to show that mammals carry out daily programmes of activity which meet four kinds of requirement, namely, for security, appropriate environmental complexity, novelty and opportunities for achievement. Within their programmes mammals perform two kinds of activity: work which relates to day to day survival, and leisure, in the form of curiosity or play, which provides experience which may prove to be of value in the long term.
The existence of behavioural needs is consistent with our knowledge of mammalian evolution. Even the earliest known mammals, living over 120 million years ago, differed from reptiles in having brain to body size ratios four to five times greater. The increase in brain size resulted largely from the massive expansion of a region of the cerebral cortex, known as the neopallium, which acts as a co-ordinating centre for sensory data, and creates a model of the world which determines subsequent action. During the 60 million year tertiary era, relative brain size increased in most orders of eutherian mammals, so that only the more intelligent survived.
Because mammals rely for their survival on collecting and analyzing data and acting intelligently, they need facilities to search for information to establish and monitor their concept of the real world; their psychological well-being depends on an environment which offers such facilities. There are two kinds of behavioural needs; psychological needs, which appear to be unique to mammals, and ethological needs which are experienced by all vertebrates. It is concluded that environmental quality for captive mammals should not just be assessed negatively, by the absence of abnormal behaviours, but more positively by the extent to which it meets their psychological needs.