Department of Zoology, University of Oxford, South Parks Road, Oxford OX1 3PS
Brain size, development and metabolism in birds and mammals
Article first published online: 20 AUG 2009
1985 The Zoological Society of London
Journal of Zoology
Volume 207, Issue 4, pages 491–509, December 1985
How to Cite
Bennett, P. M. and Harvey, P. H. (1985), Brain size, development and metabolism in birds and mammals. Journal of Zoology, 207: 491–509. doi: 10.1111/j.1469-7998.1985.tb04946.x
- Issue published online: 20 AUG 2009
- Article first published online: 20 AUG 2009
- (Accepted 12 March 1985)
Recent hypotheses that variation in brain size among birds and mammals result from differences in metabolic allocation during ontogeny are tested.
Indices of embryonic and post-embryonic brain growth are defined. Precocial birds and mammals have high embryonic brain growth indices which are compensated for by low post-embryonic indices (with the exception of Homo supiens). In contrast, altricial birds and mammals have low embryonic and high post-embryonic indices. Altricial birds have relatively small brains at hatching and develop relatively large brains as adults, but among mammals there is no equivalent correlation between variation in adult relative brain sizes and state of neonatal development.
Compensatory brain development in both birds and mammals is associated with compensatory parental metabolic allocation. In comparison with altricial development, precocial development is characterized by higher levels of brain growth and parental metabolic allocation prior to hatching or birth and lower levels subsequently. Differences between degrees of postnatal investment by the parents in the young of precocial birds versus precocial mammals may result in the different patterns of adult brain size associated with precociality versus altriciality in the two groups.
The allometric exponent scaling brain on body size differs among taxonomic levels in birds. The exponent is higher for some parts of the brain than others, irrespective of taxonomic level. Unlike mammals, the exponents for birds do not show a general increase with taxonomic level. These pattcrns call into question recent interpretations of the allometric exponent in birds. and the reason for changes in exponent with taxonomic level.