UC Riverside

Individuals may adjust parental effort with respect to the value of the current brood versus future reproductive potential, and the adrenocortical stress response may mediate parental allocation decisions by diverting energy investment towards self-maintenance. In this dissertation, I test the hypotheses that the stress response negatively correlates with elaboration of the sexually selected trait of song complexity and with parental effort, that paternal and maternal effort correlate with song complexity due to the signaling function of song, and that predation risk may induce relationships between song complexity, the stress response, and parental effort by elevating costs of parental care. I used song sparrows (Melospiza melodia) as a model species. Song sparrows are monomorphic, but males alone sing a complex sexually selected song. I recorded nesting and singing behavior, assessed parental responses to experimentally elevated perceived predation risk, and measured the stress response following capture-induced stress. Additionally, to assess whether modulation of the stress response may help organisms adapt to anthropogenic disturbance, I investigated differences in stress physiology and condition within an urban song sparrow population. I found that two components of song complexity correlated distinctly with the stress response and maternal and paternal effort, suggesting that song may fulfill a multiple messaging function, and challenging the idea that negative correlations between the stress response and elaboration of sexual ornaments are established during development. Further, predation risk induced relationships between both song traits and the stress response and some metrics of maternal and paternal effort, suggesting that predation risk may modify the extent to which song signals paternal benefits, maternal allocation on the basis of song traits, and fitness ramifications of differences in stress physiology. On the inter-individual level, I found little evidence that smaller stress responses translate into higher parental effort. Indeed, paternal effort positively correlated with the stress response, perhaps because males with larger stress responses are well prepared to evade predation risk. Finally, song sparrows breeding in areas with high anthropogenic disturbance levels did not suffer declines in condition and tended to have smaller stress responses, suggesting that sparrows successfully cope with selective pressures unique to urban areas.