Adapted from an article by Rick Simpson
Wader Quest Newsletter, email: [email protected]
So, what exactly are all those wading
birds out there on the mudflats eating
with such enthusiasm? The answer is
benthos, also known as wader food.
Benthos is the flora and fauna found on
the bottom, or in the bottom sediments,
of a sea or ocean.
Wader bills have developed to take
advantage of all forms of benthos as
prey. (See the definitions of different
type of benthos below.)
Long bills that penetrate the mud such
as those of Godwits will search for
Species feeding in this way will be
doing so without the benefit of sight so
their bills are sensitive to touch and
Their bills have nerve endings known
as Herbst corpuscles, which can detect
the difference in pressure produced by a
solid object in the wet mud.
Many waders that feed in this way
demonstrate rhynchokinesis, where the
upper mandible can be bent to allow the
bird to strike and capture prey.
This ability to forage blind means they
are equally able to forage at night as
they are during the day.
Short bills such as those of the Plovers
will be taking mostly epibenthos and
some endobenthos organisms that live
near or just under the surface as they
forage primarily by sight. This would
obviously suggest that feeding at night
would be a disadvantage. It is for this
reason that Plovers have such
proportionally large eyes to maximise
light gathering to facilitate night
There is also a school of thought that
suggests they may also be able to forage
by hearing prey which would also not
be affected by the light level.
Some waders with medium-length
bills, such as Red Knot may employ
both methods of feeding—mainly
tactile on the wintering grounds where
it forages for endobenthos and mainly
visual on the breeding grounds where it
forages for nonbenthic creatures away
from the benthic zone.
These species have sensitive bills for
tactile feeding and forward-facing
vision for visual feeding.
The more delicate recurved sweeping
bills of Avocets will be seeking
epibenthic prey on the surface of the
mud and hyperbenthic organisms that
are suspended in the water.
There are two types of benthos:
Zoobenthos: comprises the animals
belonging to this group.
Phytobenthos: comprises the plants
belonging to this group.
Both types of Benthos can be
subdivided by size.
Macrobenthos: Visible organisms of a
length greater than 1mm. It includes
polychaete worms (worms with bristles
like lugworms etc.), bivalves (seashells
with two halves like cockles, oysters,
clams and mussels), echinoderms (star
fish, sea urchins etc.), sea anenomes,
c o r a ls, s p o n g e s, s e a s q u irts,
turbellarians (flatworms), crabs,
lobsters and cumaceans (comma
Meiobenthos: Organisms that are
between 1mm and 0.1mm in size. It
includes nematodes (roundworms),
f o r a m i n i f e r a s, w a t e r b e a rs,
gastrotriches (hairybacks), copepods
and ostracods (seed shrimps).
Microbenthos: Organisms under
0.1mm in size. It includes bacteria,
diatoms (algae), ciliates, amoeba and
They can also be divided by their
Endobenthos: living buried, or
burrowing in the sediment.
Epibenthos: living on top of the