Productivity of an iconic waterbird, the Common Loon, is decreasing across the southern portion of its breeding range

The Common Loon ( Gavia immer) is an iconic waterbird of the northern wilderness and an indicator of the health of aquatic ecosystems. We conducted a benchmark comparison of productivity rates and long-term trends in productivity (6-week-old young raised per territorial pair) from 45 591 breeding events across 12 different study populations throughout the southern portion of species’ breeding range in North America. While all regions showed long-term mean productivity rates at or above the threshold considered necessary for population stability (0.48 chicks fledged per territorial pair), we found significant declines in productivity (ranging from −0.17% to −2.8% per year) in seven regions, nonsignificant but downward trends in four others, and a nonsignificant increase in one region (Maine). Although productivity is only one of three demographic parameters that dictate the stability of a population, long-term decreases in productivity could signal looming population declines in Ontario, the Prairie, and Atlantic provinces, New York, Massachusetts, and New Hampshire. We suggest that a variety of region-specific anthropomorphic and natural factors, in addition to increased rainfall secondary to climate change are at fault for such declines. Identifying causes of productivity decline might lead to successful efforts to mitigate contributing factors, thus stabilizing or increasing loon populations.