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Open Access Publications from the University of California


The International Journal of Comparative Psychology is sponsored by the International Society for Comparative Psychology. It is a peer-reviewed open-access digital journal that publishes studies on the evolution and development of behavior in all animal species. It accepts research articles and reviews, letters and audiovisual submissions.

Volume 11, Issue 3, 1998

Research Article

Suckling Behavior in Domestic Goats: Interaction Between Litter Size and Kid Sex

Studies of milk allocation in polytocous species provide the opportunity to investigate the effects of offspring number and sex ratio on maternal investment. In these species maternal control over milk allocation is more difficult because physiological limits on milk production may stimulate sibling competition. This study investigated the nursing behavior of domestic goats bearing twins or singletons in an experimental situation for the first 47 days post-partum. Milk yield and composition did not correlate with litter size, kid weight, or with the behavior of kids. Males were heavier than females, but there were no sex differences in behaviors related to nursing. Milk allocation differences existed between twins and singletons, even though, on the average, there were no significant weight differences. However, one twin was always larger than the other. Twins spent less time in proximity to the mother than did the singletons, and were more responsible for achieving proximity to the mother. These results suggest that nursing behavior was more affected by litter size than by sex of young, although there might be an interaction between both, that early mother-young interactions were different for twins and singletons, and that kids played an active role in the allocation of milk and its conversion to body weight.

Animal Cognition in Relation to Farm Animal Welfare: The Need for a Different Approach

Reviewing various ideas about animal cognition, including the radically different approach developed by Maturana and Varela (1987), brings to light serious concerns about the ability of the current science of cognitive ethology to address issues of animal welfare or to provide useful interpretations of animal thinking and awareness. The proposition that farm animal welfare will be properly assessed only when much more is known about the cognitive abilities of the animals concerned is critically discussed. This principle is supported, but the current means of achieving it are questioned. It is argued that a broader scientific basis is needed to enhance a cognitive ethology that is merely an additive combination of behavioural observation and information-processing models of cognition.

Making Place for a Comparative Scientist: Robert Means Yerkes at Harvard, 1902-1917

During the first decade of this century, Robert Meams Yerkes struggled to make a place for himself within Harvard University's Division of Philosophy as a comparative scientist. From the perspective of a young assistant professor, Yerkes'diary and letters permit a glimpse into the ail-too familiar struggle of establishing career and family.