Title: Spatiotemporal dynamics of songbird breeding in arctic-boreal North America
Description: The high northern latitudes of North America are undergoing rapid climatic change with acute impacts to the ecosystems in which millions of songbirds breed each year. The goal of this dissertation is to improve understanding of how concurrent and interacting changes in environmental and land surface conditions influence annual movements and habitat selections of long distance migratory birds who must navigate the mosaic of changing North American ecosystems. Chapter 1 presents novel automated bioacoustic methods for estimating arrival dates of the songbird community to their arctic breeding grounds. Automated acoustic networks could vastly expand the spatiotemporal coverage of wildlife observations. However, the enormous datasets that autonomous recorders typically generate demand automated analyses that remain largely undeveloped. Chapter 1 demonstrates novel machine learning and signal processing techniques for estimating songbird community arrival dates near Toolik Field Station which agreed well with traditional survey estimates and were strongly related to the landscape’s snow free dates.

Daily variations in vocal activity were more strongly influenced by environmental conditions prior to egg-laying dates. The success of the approaches presented in Chapter 1 indicate that variation in songbird migratory arrival can be detected autonomously. Widespread deployment of this advance could provide avian monitoring on a scale large enough to enable global-scale understanding of how climate change influences migratory timing of avian species. Chapter 2 examines potential future changes in habitat suitability for for two songbirds breeding throughout North America’s high northern latitudes – a tundra-nesting species (Lapland Longspurs (Calcarius lapponicus)) and a shrub-nesting species (White-crowned Sparrows (Zonotrichia leucophyrs)). By the late 21st century, models based on both climate and vegetation projected habitat suitability for Lapland Longspurs decreased across nearly all of the study domain (54-96%), while that for White-crowned Sparrows decreased in 69% of North America’s high northern latitudes.

For both species, currently unsuitable habitats in northern Canada and Alaska are projected to provide suitable breeding habitat in the future. In contrast, models based solely on climate showed more drastic declines in habitat suitability for both species (Lapland Longspur, ~100% and White-crowned Sparrow ~80%). This discrepancy between model projections demonstrates that the future availability of suitable songbird breeding habitat for both species will be strongly dependent on how both the vegetation and climate– as opposed to climate alone - of northern ecosystems respond to ongoing climate change. Chapter 3 investigates the environmental and ecological drivers of migratory movements of songbirds breeding at high northern latitudes. For North America alone, there is overwhelming evidence of major shifts in seasonality of meteorological conditions, snow cover, and vegetation phenology. Few studies have focused on how this suite of changes impacts long distance migratory species that annually navigate throughout the spatially and temporally dynamic mosaic of ecosystems because of technological constraints in animal tracking.

However, recent advances in GPS technology have generated units small enough to be placed on songbird species. In 2016-2018 a total of 55 American robins (Turdus migratorius) were tracked during their spring migration through the Canadian boreal forest en route to their breeding grounds. We found a significant trend towards earlier arrival of robins to the Canadian boreal forest over the past quarter-century, consistent with advances in spring environmental conditions. Robin stopover timing at our tagging site was delayed in response to later seasonal snowmelt, but triggered by adverse environmental conditions. Individuals breeding in regions with shorter snow-free seasons moved faster than individuals breeding in areas with longer snow-free seasons and selected locations with less favorable environmental conditions. Overall, arrival timing to breeding grounds was negatively related to snow depth and positively related to snowmelt timing. Migratory movements and timing of American robins are highly tied to seasonal environmental dynamics en route to their breeding grounds.

Our findings present a unique, mechanistic understanding of how migratory birds navigate highly dynamic ecosystems. In light of rapid global change, the use of multi-disciplinary, spatially explicit approaches similar to the ones used in this dissertation will be critical for understanding how avian taxa breeding at high northern latitudes may respond to ongoing and future change. This is important for investigating both regional and global impacts because species breeding in arctic-boreal zones perform key ecosystem services around the globe.