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Human influence on ecosystems is rapidly expanding, and one consequence is the increased availability of human food subsidies to wildlife. Human food subsidies like refuse and food scraps are widely hypothesized to be 'junk food' that is nutritionally incomplete; however, the impacts of 'junk foods' on the health and fitness of individual organisms remain unclear. In this study, we aimed to understand how human food consumption affects the body condition and fecundity of a generalist predator, the Steller's jay (Cyanocitta stelleri). We used stable isotope analysis to quantify individual human food consumption (using δ13C as a proxy), estimated individual body condition based on body mass and feather growth bar width and assessed jay fecundity. Adults consumed more human food than juveniles on average, and we observed sex-specific responses to human food use where male body condition tended to increase, whereas female body condition tended to decline with human food consumption. However, fecundity was not strongly related. Thus, we found some evidence for the 'junk food' hypothesis in this system, which suggests that human foods may not be an equal replacement for natural foods from a nutritional perspective, especially for females. Human foods tend to be carbohydrate rich, but protein poor, which may benefit males because they are larger and limited overall by calorie intake. Females, particularly reproducing females, are more nutritionally limited and thus may experience fewer benefits from 'junk food'. Our study advances knowledge of human–wildlife interactions by increasing the resolution of our understanding of the fitness benefits, or detriments, experienced by individuals that consume human foods. [ABSTRACT FROM AUTHOR]

Protected areas safeguard biodiversity and provide opportunities for human recreation. However, abundant anthropogenic food subsidies associated with human activities in protected areas can lead to high densities of generalist predators, posing a threat to rare species at broad spatial scales. Reducing anthropogenic subsidies could curb populations of overabundant predators, yet the effectiveness of this strategy is unclear. We characterized changes in the foraging ecology, body condition, and demography of a generalist predator, the Steller's jay, three years after implementation of a multi-faceted management program to reduce anthropogenic subsidies in a protected area in California. Stable isotope analysis revealed that the proportional contribution of anthropogenic foods to jay diets declined from 88% to 47% in response to management. Overlap between jay home ranges decreased after management began, while home range size, body condition, and individual fecundity remained stable. Adult density in subsidized areas decreased markedly from 4.33 (SE: ±0.91) to 0.65 (±0.20) jays/ha after the initiation of management, whereas density in unsubsidized areas that were not expected to be affected by management remained stable (0.70 ± 0.22 pre-management, 0.58 ± 0.38 post-management). Thus, the response of jays to management was density-dependent such that reduced densities facilitated the maintenance of individual body condition and fecundity. Importantly, though, jay population size and collective reproductive output declined substantially. Our study provides evidence that limiting anthropogenic subsidies can successfully reduce generalist predator populations and be part of a strategy to increase compatibility of species protection and human recreation within protected areas. [ABSTRACT FROM AUTHOR]