In an urbanizing world, residential lands present an opportunity for conservation of biodiversity right in our backyards. Informed conservation necessitates a mechanistic understanding of how development influences animal populations and communities. Birds nesting in residential lands are less productive in urban yards than rural yards. Urban yards also have higher densities of potential predators, but lower per capita predation, indicating that direct predation is not entirely responsible for lack of productivity. I suggest that fear effects, also known as non-lethal effects, could be a mechanism by which predators exert indirect influence on bird parental behavior and nestling condition in urban yards. I investigated how fear of adult-consuming predators interacts with urbanization to affect parental behavior and nestling condition in residential yards across an urban gradient in western Massachusetts. We conducted a predator playback experiment on nesting house wrens (Troglodytes aedon), measuring nestling condition and parental behavior. We found that nestlings exposed to predator playbacks and in urban yards had reduced mass compared nestlings exposed to control playbacks and in rural yards. To varying degrees across the gradient, predator playbacks suppressed provisioning rates and brooding durations. Nestling age, clutch size, habitat structure, and microclimate were also related to provisioning rates and brooding durations. In an associated study, we examined the relationship between landscape-scale and parcel-scale features and mammal community structure by deploying camera traps in the same yards. Many mammal species are potential nest and/or adult-consuming predators of house wrens, so changes in the mammal community could alter trophic dynamics and influence fear effects across the gradient. Mammalian community composition varied significantly across the urban gradient, and species richness responded non-linearly to urbanization, with peak richness in the suburbs and in yards with larger mean tree diameters. These results, coupled with fear’s influence on bird parental behavior and nestling condition, highlight the importance of considering both direct and indirect effects of trophic dynamics in urban systems
