Recent reports of widespread insect declines have sparked conservation concern for both insects and insectivorous bird populations in North America and beyond, since the magnitude of declines and their effects remain unclear. Here, I present research that aims to inform population trends and linkages for these closely connected groups, by bringing together data from biological resurveys at local scales, and large scale literature synthesis and time-series datasets. In Chapter 1, I first present an overview of insect declines, which focuses on key knowledge gaps and challenges for understanding insect declines. Next, I present research proposing that insect monitoring efforts can benefit from increased methods alignment with other programs, helping multiply the usefulness of data and forming the basis for insect monitoring networks. In Chapter 2, I bring together 4000+ insect population time series to demonstrate that insect population variability is higher than that in vertebrate taxa. I then characterize patterns in this population variability across geographic traits (latitude and biome), time series traits (duration and start date) and species size, finding higher variability at higher latitudes, for smaller species, and for older, shorter time series, which can help inform population trend estimation and extinction risk assessments. In Chapter 3, I present results from a paired, bird-insect biological resurvey from Great Smoky Mountains National Park, TN, U.S.A., where myself and others revisited sites originally surveyed in the late 1940s to collect data on bird and insect community change. Because this protected area serves as a refuge from some anthropogenic pressures (e.g., habitat loss and light pollution), but is still vulnerable to others (e.g., invasive pests and climate change), it serves as a useful natural laboratory for evaluating community change. Using Bayesian n-mixture modeling to account for imperfect detection, I find that populations of many bird species have declined markedly since the 1940s, and that insect communities have declined at some sites but increased at others. Changes in the two communities are correlated, and likely driven by the combination of habitat change and climate change.

Climate change is driving a rapid but highly variable redistribution of life on Earth, comparable in scale and magnitude to changes historically only seen over tens of thousands of years. Despite increased research effort, the complex mechanisms driving these changes in geographical distribution of species, or ‘range shifts’, remain only superficially understood. Attempts to understand the processes underpinning species responses are hampered by the paucity of comprehensive, longterm datasets, few theoretical frameworks, and lack of strategic direction and cross-fertilisation with related ecological fields. As an emerging, dynamic field, range shift ecology would benefit from integrating concepts and approaches from other related, more established areas of research, such as invasion ecology. Here, we use a systematic literature review and bibliographic analysis to assess the level of knowledge exchange between range shift ecology and invasion ecology. We found that while the two fields are inherently strongly related, the level of exchange and integration of ideas via citation networks does not reflect the closeness of the fields in terms of concepts, theories, and practice. Although range shift papers cite invasion papers more often than vice versa, the citation rate is generally quite low for both. These findings are evidence of the increasing need to move away from discipline-focused interpretation and communication of scientific results, towards greater research integration and connection between related ecological fields. Increased knowledge and data exchange between range shift and invasion fields could improve mechanistic understanding of range shifts and species invasions under climate change, enhance the predictive capacity of models and better inform management and conservation efforts.