Red-throated Loon in Winter
MARCH 4, 2024
The red-throated loon is the smallest loon species in the world. Lithe and elegant, it dons an understated silver and white plumage in the winter.
From my spot on the shore, I watched this juvenile red-throated loon (Gavia stellata) approach within minimum focal range as it pursued a small school of fish into the shallows. On two occasions, the formidable hunter dove and attacked the school from below, driving the panicked fish right out of the water and into the air, only to grab them upon their inevitable return to the water. This loon will probably relocate to a coastal lake in the Alaskan Arctic or even Alaskan interior wetlands by May. The Red-throat's ability to achieve flight without a long "runway", unique among loon species, allows them to nest on smaller lakes that are not accessible to other species and to forage further away from their nesting site. Despite these adaptations, their breeding effort and success widely fluctuates from year to year. Their population plummeted by half over a narrow 16-year period starting in 1977. The numbers have since stabilized, but risks remain, including habitat loss, nest predation and being netted as bycatch. Disturbance by engine noise from ships and helicopters can even induce them to abandon nests.
This juvenile is likely still lingering in nearby coastal marine waters of the San Francisco Bay, where I found it several months ago. Like many fish-eating specialists, they are drawn to estuarial discharges proximate to upwelling ocean currents that bring colder, nutrient-dense water up toward the surface in summer and fall. These conditions support photosynthesis by phytoplankton and algae which increases oxygen levels locally, fueling higher concentrations of zooplankton, which in turn, feed larger numbers of fish. Upwelling usually decreases in winter as the prevailing winds tend to cause the opposite phenomenon and there is less of a difference in temperature throughout the water column. But a variety of factors can support continued upwelling of resource-rich water and this is why the fish-loving loons are often found in such habitats, both for wintering grounds and for essential refueling stopover sites during migration. Their consistent reliance on these limited habitats increases their vulnerability to localized pollution events including oil spills. Despite being rated low in terms of risk of extinction -- with over 250,000 individuals worldwide -- they are on the US Fish and Wildlife Service's radar as a "species of special concern" and their use as an indicator species of habitat health has been studied. We are only scratching the surface of knowledge of their natural history and resilience in a changing climate. Like so many species, I am hopeful that they will thrive long enough for us to learn.