The Importance of Off-Channel Ponds to Wintering Waterbirds along the American River in Sacramento, California: An Initial Assessment

We studied waterbird use of ponds adjacent to the Lower American River in Sacramento County, California during the winters of 2021–2022 and 2022–2023. We surveyed waterbirds at Arden and Urrutia ponds, the two largest ponds along the river, which have been proposed at various times for elimination or modification to mitigate for impacts of riverine flood control work. We summarized numbers recorded at Urrutia Pond during 2010–2017 Christmas Bird Counts (CBCs) and compared numbers of waterbirds using ponds to the numbers recorded during 2014–2022 counts of the entire Lower American River. Our surveys showed that the ponds were used by a high diversity and abundance of waterbirds, including geese, ducks, cormorants, coots, and a newly established pair of Bald Eagles (Haliaeetus leucocephalus). The CBCs recorded an average of >2,000 Canvasbacks (Aythya valisineria) at Urrutia Pond, nearly the entire population on the Lower American River. Our surveys found that high numbers of diving ducks moved daily from daytime foraging areas on the river to ponds for night-roosting, presumably to conserve energy and avoid predation. Peak numbers of the Bufflehead (Bucephala albeola), Common Goldeneye (B. clangula), and Common Merganser (Mergus merganser) on ponds represented 91–134% of the total populations of these species counted on the entire Lower American River. Our results are preliminary because of the relatively few surveys over only a few years but they suggest that the currently proposed elimination of Urrutia Pond has the potential to affect the Lower American River populations of diving ducks and other waterbirds. Retention of Arden Pond and a portion of Urrutia Pond, would reduce the potential for impacts to diving ducks and other waterbirds that currently use the ponds.