Energetic Costs of Aggression in the Northern Cardinal

Territorial aggression during the nonbreeding season has not been sufficiently studied, especially in a natural system. There has been some evidence to suggest that the steroid hormone precursor, dehydroepiandrosterone (DHEA) may regulate male aggression during the nonbreeding season, rather than testosterone. This study aimed to investigate the effects of energy status (through food supplementation) on nonbreeding aggression in the Northern Cardinal and add to the pre-existing evidence of a DHEA-mediated mechanism of aggression. It was hypothesized that if aggression was maintained for an extended period of time, metabolite levels would favor energy usage (more glycerol and less triglycerides) compared to a bird who has exhibited aggression for only a short period of time. Furthermore, birds with greater food security (i.e., FS birds) will exhibit more aggression, and hence more DHEA and less corticosterone (CORT), while expending more energy than control (CON) birds with less food security. However, the results of the study were inconclusive. While metabolite concentrations did not show a significant difference between treatment groups, it did appear that CORT was slightly lower in food supplemented birds and DHEA was higher and increased more drastically during capture than control birds. However, statistical analyses found that none of these differences observed from graphical representation of the data were significant. It was concluded that this can be attributed to a very small sample size and large individual variance. Therefore, we could not conclude with certainty that food-supplementation affected aggression or whether aggression was regulated by DHEA