Date of Award


Degree Type


Degree Name

Master of Science




Dr. S. MacDougall-Shackleton


Non-breeding black-capped chickadees form linear dominance hierarchies in the winter. Dominants establish and maintain status by repeatedly directing aggression towards subordinates despite having regressed testes and likely also basal levels of testosterone. Melatonin has been shown to facilitate aggression in some animals under non-breeding conditions. The first aim of this study was to investigate whether melatonin was associated with aggressive black-capped chickadee dominant-subordinate interactions during the establishment of dominance status. The second aim of this study was to determine whether exogenous melatonin affected aggressive vocalizations more than non-aggressive vocalizations. Plasma melatonin was not significantly correlated to aggression. Moreover, exogenous melatonin treatment had no effect on aggressive or non-aggressive vocalizations. Results from this study therefore indicate that there is no relationship between melatonin and aggression and also no relationship between melatonin and dominance status in black-capped chickadees.



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