Population-level estimates of offspring sex ratios in birds typically approximate parity whereas biased ratios within nests are not uncommon. In sexually dimorphic raptors, the costs and relative fitness benefits of rearing male and female progeny vary with changing environmental circumstances. This may lead to substantial deviations from balanced investment in offspring of a particular sex by individual parents. Based on a 13-year dataset for breeding Merlins Falco columbarius in Saskatoon, Canada, we used a model selection approach to assess the influence of parents, nest-mates and nesting area on brood sex ratio during the nestling phase. The best model for predicting brood sex ratio included age of the breeding male and brood size for each nest ( n = 127); nests with older male breeders and smaller brood sizes had more female young. The population-level annualized average proportion of male offspring was 0.472 ± 0.017 (mean ± standard error), but tended towards greater production of female young during an initial period of population growth (8 years, 10–21 pairs; proportion male 0.435 ± 0.031) versus a period when the population fluctuated around a presumed carrying capacity (11 years, 24–33 pairs; proportion male 0.500 ± 0.017). Energetics appears to be a finely tuned mechanism driving sex ratio allocation in Merlins at both brood and population levels. Provisioning food for young in the nest represents the male's ability to successfully capture prey, reflecting his age and/or experience, as well as the availability of prey to the male. Confounding this mechanism to determine sex ratio allocation are the pressures created by population dynamics that dictate competition for resources both within the nest (brood size) and external to the nest (population density). 中文翻译： 鸟类后代性别比例的种群水平估计通常近似于均等，而巢内有偏差的比例并不少见。在两性异形的猛禽中，饲养雄性和雌性后代的成本和相对健康益处随着环境条件的变化而变化。这可能会导致父母个体对特定性别后代的平衡投资出现重大偏差。基于在加拿大萨斯卡通繁殖Merlins Falco columbarius的 13 年数据集，我们使用模型选择方法来评估父母、巢伴侣和筑巢区域在雏鸟阶段对育雏性别比的影响。 预测育雏性别比的最佳模型包括繁殖雄性的年龄和每个巢的育雏大小（ n = 127); 年长的雄性育种者和较小的育雏规模的巢穴中有更多的雌性幼崽。雄性后代的种群水平年化平均比例为 0.472 ± 0.017（平均值 ± 标准误差），但在种群增长初期（8 年，10-21 对；雄性比例为 0.435 ± 0.031），雌性后代的产量趋于增加) 与人口围绕假定承载能力波动的时期相比（11 年，24-33 对；男性比例 0.500 ± 0.017）。能量学似乎是一种精细调整的机制，可在 Merlins 的育雏和种群水平上驱动性别比例分配。为巢中的年轻人提供食物代表雄性成功捕获猎物的能力，反映了他的年龄和/或经验，以及雄性猎物的可用性。