Fear, Parental Behavior, and Community Structure in Residential Lands

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

Perilous Choices: Landscapes of Fear for Adult Birds Reduces Nestling Condition Across an Urban Gradient

Predator fear effects influence reproductive outcomes in many species. In non-urban systems, passerines often respond to predator cues by reducing parental investment, resulting in smaller and lighter nestlings. Since trophic interactions in urban areas are highly altered, it is unclear how passerines respond to fear effects in human-altered landscapes. Nestlings of passerines in urban areas also tend to be smaller and lighter than their rural counterparts and are often exposed to high densities of potential predators yet experience lower per capita predation-the predation paradox. We suggest fear effects in urban habitats could be a significant mechanism influencing nestling condition in birds, despite lowered predation rates. We manipulated exposure of nesting birds to adult-consuming predator risk in residential yards across a gradient of urbanization to determine the relative influence of urbanization and fear on nestling condition. We found nestlings had reduced mass in nests exposed to predator playbacks as well as in more urban areas. Despite lower per capita predation rates in urban areas, fear effects from increased predator densities may influence passerine fitness through reduced nestling condition. As urban development expands, biodiversity conservation hinges on a deeper mechanistic understanding of how urbanization affects reproductive outcomes