Studies of animals often report a greater sensitivity of one sex to poor rearing environments. However, it is unclear whether size differences associated with sex, sex itself, or other factors are responsible for differences in performance. While the greater nutritional requirement of the larger sex is a plausible explanation for increased sensitivity (i.e., size-dependent vulnerability), other hypotheses suggest that size-independent traits may have effects on the fitness of offspring (i.e., sex-dependent vulnerability). For example, the heterogametic sex may be more vulnerable to expression of sex-linked recessives in poor environments, or sex-specific phenotypes may have negative effects (e.g., increased testosterone in males). We examined support for these hypotheses through the use of meta-analytic techniques based on the published literature on avian species. Our results revealed small, nonsignificant effects for hypotheses of size- and sex-dependent susceptibilities alone. Application of a multivariate meta-analytic technique (meta-regression) suggests a joint influence of sexual size dimorphism and clutch size in explaining sex-specific patterns of vulnerability. These findings suggest that none of the proposed hypotheses tested here on their own can sufficiently explain the observed patterns and that additional factors must be considered in order to explain the diversity of patterns of sex-specific sensitivity observed in the literature.

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Climate and hydrologic variability are defining characteristics of California rivers. Recently, the region experienced an unprecedented drought, and the probability of similarly warm, dry conditions is predicted to increase. In addition to warming air and water temperatures, climate change projections predict increased flooding and sea level rise, likely aggravating the water resource issues that already challenge the western United States. Water managers balance many public interests, including the conservation of native fishes, such as the Chinook Salmon Oncorhynchus tshawytscha. Given projected changes in climate and hydrology, there is an urgent need to understand how salmon respond to these conditions. In this study, we examined how young salmon responded to extreme drought (2012–2015) versus flood (1998–1999) conditions in the Yolo Bypass, a floodplain–tidal slough complex of the Sacramento River, California. We found that the diets of juvenile Chinook Salmon were dominated by aquatic–riparian insects during flooding and were dominated by zooplankton during the drought. Although juvenile salmon that were caught during the drought seemed to have eaten a higher number of prey items on average, they also had higher metabolic costs. Therefore, it is likely that juvenile salmon must augment their foraging behavior to offset higher temperatures and prey shifts. Finally, preferentially consumed, calorically valuable prey (i.e., larger zooplankton and aquatic–riparian insects) have become rare due to habitat degradation and biological invasions, and resource managers must consider re‐establishing productive off‐channel habitats, such as riparian corridors, floodplains, and wetlands.