In virtually all species, reproduction must be precisely timed to coordinate breeding and rearing of offspring with favorable conditions. It is imperative for individuals to time the highest energetic cost to themselves or highest needs by offspring with greatest food availability in either abundance or nutrient make-up. To accomplish this, individuals must integrate signals conveying both internal and external status and accordingly alter the activity of the reproductive axis. To date most efforts to identify variation in control mechanisms for reproduction in seasonally breeding animals have focused on the brain as the initiator for reproduction. However, recent studies have re-directed attention to two other potential tissues, the pituitary and ovary, where variation in brake sensitivity may be important. To this end, a series of experiments were performed in two songbird species to elucidate the hormonal role in timing of breeding and the interaction of an energetic trade-off on the decision to breed in both males and females. I used two species, the wild dark-eyed junco (Junco hyemalis) and the wild-caught captive house sparrow (Passer domesticus) as model systems to address the following questions: 1) What physiological mechanisms explain individual variation in onset of gametogenesis? And 2) How are mechanisms of energy integrated with the reproductive axis’ control of reproduction and timing of breeding to regulate energetic trade-offs? Specifically, we focused the role of testosterone in males (Chapter 2), and mechanisms downstream of the hypothalamus in females (Chapter 3). Next, in Chapter 4, the question of whether an energetic demand would reduce sperm quality was addressed. Lastly, in Chapter 5, we asked if an energetically costly immune challenge would result in the delay of clutch initiation. The results of these studies demonstrate the significant differences between sexes in the signals conveying an individual’s internal and external status in order to alter activity of the reproductive axis, and therefore timing of breeding. Collectively, these findings provide further evidence that females are ‘in the driver’s seat’ for onset of breeding and should be the focus of future research.