SCENT MARKING AND RESOURCE DEFENSE BY MALE COYPUS (MYOCASTOR COYPUS)

The alternative ideas that scent marking functions mainly in intrasexu al competition or for attracting or stimulating mates were tested usin g data from a 16-year study of coypus, Myocastor coypus. Male coypus h ave a large anal gland, specialized for marking. Despite year-round br eeding, the anal gland shows regular seasonal variation with marked en largement in October-December, The analysis supported the hypothesis t hat this seasonal increase in glandular activity was linked to intrase xual competition: the size of the autumn peak was correlated with the increase in male numbers from the previous season and with the frequen cy of fighting scars. There were no relationships between gland size a nd any measures of the availability of mates. Increased scent marking may have been part of the response by resource-holding males to male r ecruits as these competed for existing territories. The timing of the autumn peak in marking and fighting may have been a response to the ac cumulation of non-resource-holding males over the summer (when recruit ment exceeded mortality in the population) and to increasing accessibi lity within previously dense wetland habitats; together, these factors may cause a switch from scramble to despotic competition and an incre ase in scent marking to help keep the costs of resource defence within economic limits.