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birdwatchersdigest.com • MARCH/APRIL’ 17 • BIRD WATCHER’S DIGEST 32
Iremember when I was a begin- ning birder and someone com- mented about mallards and their
vegetarian diet. I was confused:
These were ducks, they swam.
I thought that everything that
swam ate fish. Don’t ducks eat
fish? Well, for the most part, no
they don’t. The dabblers are vegetarians. The divers—goldeneyes,
scaup, scoters—surely,
they eat fish, don’t they?
Nope. Diving ducks are
also vegetarians, although
some species eat mollusks.
It turns out that only
the most un-duck-like ducks eat
fish: the mergansers. I say “most
un-duck-like” in that they do not
have the classic, broad bill we
associate with ducks. That broad
bill is great for doing all sorts of
things, but catching fish is not one
of them. It seems so obvious to
me now, with many years of expe-
rience under my belt. But when
I learned many years ago that
ducks generally don’t eat fish, it
was a revelation.
I remember experienced bird-
ers also pointing out that the nar-
row, almost cormorant-like bill
of mergansers was serrated on
the cutting edge, so those slippery
fish don’t get away. Of course,
even specialists show some degree
of variability, and mergan-
sers will eat frogs, tadpoles,
aquatic invertebrates, and
certainly a bit of salad here
and there. I am devoting this
column to the identification
of mergansers, with focus
on the females, as these are the
more difficult ones. As we discuss
their identification, we can also
delve into the ecology of the three
North American mergansers, and
what makes their lifestyles differ-
ent from each other.
Mergansers eat fish, and fish
are widespread across the continent. So, as you would expect,
Mergansers
