As just now there is a lot of talk on the list of waterbirds associating with
each other, and often using other species as 'beaters', it may be of some
interest to repeat a little piece that I wrote some five years ago, about an
association I watched 25 years ago, in Bodega Bay, California.
Wim Vader
BUFFLEHEADS SAVE PHALAROPES
In 1979-80 I spent a sabbatical year at the Bodega Marine Station in Bodega
Bay, California. The shallow Bodega Harbor is a wonderfully rich bird area, and
I used much of my spare time watching all the loons, grebes, pelicans, ducks
and shorebirds. Among my favourite ducks were the cheerful and active
Buffleheads Bucephala albeola, feeding by diving to the bottom in tight flocks
in certain areas of the harbor, where the bottom clearly was covered with large
amounts of green Ulva-type algae, full of small crustaceans, probably what the
ducks fed on in the first place.
These flocks were intermittently active, but also used a lot of time lazing,
displaying and preening. Feeding activity seems to be contagious, as usually
either all the Buffleheads in a flock were actively diving and feeding, or none
of them were. (As an amphipod specialist I did identify the most common
Crustacea in the green algae there, but I suppose the names will not tell you
much, so I omit them).
In November 1979 there was a sizeable wreck of phalaropes, and for a few weeks
we found weak or dead phalaropes everywhere in the area, even on our own porch
in the sand dunes. Soon, however, a very interesting pattern appeared, in that
the surviving phalaropes clearly used the feeding Bufflehead flocks as food
source. I collected a series of data (never published), that showed that as
soon as a Bufflehead flock started diving and feeding, phalaropes arrived from
near and far and associated with the ducks. What happened was that the ducks
dove up the clumps of green algae, and ate them at the surface. Meanwhile a
number of the small crustaceans in the algal clumps escaped, and these clearly
formed the main attraction for the phalaropes.
As soon as the Bufflehead-flock stopped diving and feeding, the phalaropes
drifted away, only to return as soon as the Buffleheads became active again.
For several weeks this feeding association continued, until in fact the only
place where one still found phalaropes , was together with the Bufflehead
flocks. Then gradually the phalaropes disappeared: died or flew away. I did not
find fresh corpses after the first week of the wreck.
There were of course many other diving birds on Bodega Harbor in this period,
but the phalaropes did not show any attraction to any of them. Apparently, the
tight flocks of Buffleheads, diving all at the same time, and bringing up
clumps of green algae full of delicious small Crustacea, were just the right
environment for the hungry and weakened phalaropes.
Has anyone else noted this type of feeding association?
Wim Vader, Tromsø Museum
9037 Tromsø, Norway
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