Effects of climate, habitat, and conservation management on an aerial insectivore, the tree swallow, and its insect prey in Massachusetts, USA

Human-driven climate, habitat, and land use changes often co-occur in ecological communities. We must consider the multiple components of global change acting on individual species and assemblages to document biological responses to environmental change and determine the mechanisms underlying these responses. Here, I examine climate, habitat, and land management impacts on a model aerial insectivore, the Tree Swallow (Tachycineta bicolor), and its insect prey. Both groups are undergoing population decline and phenological shifts in many parts of the world; however, the magnitude and mechanisms of these shifts are not well understood. I first document the impacts of temperature and precipitation on fall flight times of 20 butterfly species with varied life histories in Massachusetts. I find many butterfly species are flying later into the fall now than they were over 20 years ago; however, the response of butterflies to fall climate is complex and often mediated by life history characteristics, like number of broods per season. I then examine the effects of climate, habitat, and insect prey abundance on Tree Swallow reproduction to determine if anthropogenic changes in the breeding habitat result in declines in reproductive performance that contribute to population decline. I find that climate and foraging habitat impact egg laying phenology, clutch size, hatching success and fledging success of Tree Swallows. For example, reproductive phenology is delayed in rainy springs and fledging success is increased in nests with open water in their foraging radius. However, I find no evidence to indicate a change in insect abundance or anthropogenic changes, including climate and land management, are driving decreases in reproductive success of Tree Swallows over time. Lastly, I examine the effects of artificial nest management on Tree Swallow reproduction across Mass Audubon conservation areas. I find habitat, density, and predation of artificial nests to be strong and often overlooked determinants of Tree Swallows reproductive performance; for example, fledging is increased in nests placed in open habitat, far from forests and developed areas. This work provides novel evidence for the impacts of local-scale nest habitat and management on Massachusetts Tree Swallows, a threatened population of aerial insectivores