COMMON LOON (GAVIA IMMER) BIOGEOGRAPHY AND REPRODUCTIVE SUCCESS IN AN ERA OF CLIMATE CHANGE

Climate change has the potential to shift and restrict ranges for a suite of species.  The primary goal of our research was to understand the factors that determine Common Loon (Gavia immer) vulnerability to climatic change at multiple scales.  We analyzed loon presence/absence in 288 lakes across the southern edge of their North American distribution using 112 abiotic and landscape-level factors.  The most significant factors explaining loon presence/absence were lake salinity, acidity, and surface area.  We used similar methods to compare loon occupancy and reproduction at a smaller scale (New England) and results from twenty potential predictors suggest that similar processes are driving loon presence/absence both continentally and within New England (lake salinity and lake surface area).  Loon productivity, on the other hand, was best predicted using the size of the lake and its drainage basin.  As few (if any) of the predictors of productivity are likely to change dramatically with climate, these outcomes suggest that future range alteration for loons due to climate change are likely to be more sensitive to annual adult survival (which will influence breeding ground settlement patterns) than environmental factors encountered on the breeding grounds.

We also explored environmental predictors of individual energetic condition.  Physiological measures may offer more information about the likelihood of loon persistence because they can identify relationships between energetic condition and breeding habitat quality.  We used blood metabolites and behavioral observations to evaluate the energetic costs of common loons breeding on lakes across a gradient of environmental, spatial, and social conditions.  We identified the number of offspring, daily maximum temperature, and latitude as the most important drivers of the energetic cost of maintaining a breeding territory.  Energetic condition deteriorated toward the southern range edge and in warmer conditions, controlling for the number of offspring produced, which suggests that loons may actually be sensitive to increasing global temperatures.  We suggest that as environmental conditions change in the coming years, blood metabolites offer a promising predictor of population collapse along range boundaries.