Common and Red-breasted Mergansers, Lake Merritt

Glen Tepke

Yesterday (12/12) evening I took a walk around Lake Merritt in Oakland and saw five Common Mergansers - three males and two females - loafing on and around the barrier floats across the lake, presumably, I thought, the same birds that had been reported by Lyla Arum.  Then when I got home I saw Lyla's post correcting her ID to Red-breasted Merganser and started to second-guess myself - had I misidentified the mergansers just because I was expecting to see Common?  So this afternoon I returned for another look and saw six Red-breasted Mergansers - five females and one male.  Definitely not the same birds I saw yesterday, so it looks like both species are currently frequenting the lake.  Like Hilary said, in my experience Red-breasted is more frequently seen there, but both species are semi-regular in winter.

Re Rusty's comment that Common Merganser has a strong preference for fresh water, the Birds of North America species account says "winters on both fresh and salt water, but most frequently on fresh water, whereas Red-breasted Merganser winters more on salt water."  I think Common Mergansers wintering on the coast are typically found in brackish lagoons and river mouths rather than the open ocean, and Lake Merritt fits the bill as a highly modified brackish lagoon.

Good birding,

Glen Tepke
Oakland/Santa Cruz

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