Introduction
In early July 1997, while visiting Silver Bay, New York on Lake George I observed a
young brood of Mallard ducks (Anas platyrhynchos) exhibiting some unusual behavior.
The birds were repeatedly diving and retreiving some type of mollusk from the bottom of
the Silver Bay Association boat marina. I recorded my observations over several days, but
did not have sufficient information to make an accurate report of the incident.
Upon returning to Silver Bay in early July 1998, two broods of Mallard ducks were
observed in the Silver Bay boat marina exhibiting the same behavior that was noted the
year before. More observations were recorded and mollusk specimens were collected and
identified.
Silver Bay, Lake George, New York
Lake George is a deep glacial lake on the eastern edge of the Adirondack
Park in New York State. At Silver Bay there are no marshy areas present. The shallow areas
are of a sandy nature, and drop off rapidly to deeper water. The area is not suitable to
traditional dabbling duck feeding behavior. The boat marina at Silver Bay where the
feeding activity was observed is uniformly 4 to 6 feet in depth. The entrance to the
marina where some diving behavior was observed is 6 to 10 feet deep. The bottom is sandy
with scattered fresh water grasses.
The Silver Bay Association has posted signage advising, Don't Feed the Ducks.
This signage also contains an explanatory note discouraging the practice of feeding the
birds. I have reason to believe that these informational signs are respected and enforced.
I saw no feeding of the ducks during the periods of observation in 1997 and 1998.
The Mallard Ducks
In
1997, a single brood (B97-1) was observed which was composed of an adult female, an adult
male (not always present, but in the area occasionally), and 8 ducklings still possessing
down feathers.
In 1998, there were two broods of Mallard ducks present. A brood (B98-1) of 5 first
winter birds (2 males, and 3 females), and a brood (B98-2) composed of one adult female
and 5 ducklings that lost the last of their down feathers by the second day of
observation.
The Diving Behavior
The diving behavior exhibited by the Mallard ducks appears to be a learned
adaptation that allows the ducks to forage on a freshwater mollusk residing in the Silver
Bay marina. I followed brood B98-2 several times after they left the marina to see if this
diving behavior would be exhibited elsewhere, it was not. The foraging of the freshwater
mollusk appeared to be the principal source of food for the ducks, though occasional
surface feeding and foraging for insects on boat hulls, dock sidings and moorings were
also noted.
When first observed in 1997, the ducklings of B97-1 were freely diving while under that
watchful eye of the adult female. They were using their feet and legs to accelerate the
dive and a stiff tail for additional leverage. Their wings remained closed during the
dives. Thirty-two dives were recorded and timed in 1997. The adult female was not observed
diving during the various observation periods.
In 1998, two
broods were observed for longer periods of time and 110 dives were recorded and timed.
Many more dives made but were not recorded. All ducks including the adult female in B98-2
were seen to dive during the observation periods, although the frequency of dives was
greater by the younger ducklings of B98-2. The dive duration times ranged from 4-12
seconds. The dives of the first winter birds of B98-1 and the adult female of B98-2 were
longer in duration than the dives of the ducklings of both B97-1 and B98-2. Over 75% of
the dives by the ducklings in B98-2 were less than 7 seconds. Over half of the dives by
the first winter ducks of B98-1 were over 8 seconds in duration. Though counts were not
actually recorded, it appeared that the mollusk recovery success per dive was in excess of
85%.
During one observation period, a clear overhead view in calm waters allowed study of
the ducks underwater to a depth of 4 to 5 feet. It was observed that the ducks were not
just diving to the bottom, but were also using their legs to maneuver themselves along the
lake bed and through the bottom grasses as they foraged for mollusks. The ducks appeared
to use their inherent buoyancy to bring them to the surface after they had obtained a
mollusk and/or stopped using their legs to keep them underwater.
During a feeding session, the dives were repeated and frequent. These feeding sessions
lasted between 15 and 20 minutes. At the end of a feeding session, the ducks would either
seek a resting spot along the shore of the marina, on a dock, or would leave the marina
all together and continue along the shoreline of Lake George to another shoreline rest
area. For the most part, the Mallard broods appeared to favor the protected cove of Silver
Bay proper. Of the study broods , diving was not noted in places on Lake George other than
in the marina area itself.
B97-1 with the youngest birds were the most predictable in their diving activity. They
remained in the marina during the entire week of observation. B98-1 and B98-2 were less
predictable regarding diving activity and were not bound to the marina, leaving it
frequently. B98-1 fed less frequently in the marina and individuals from that brood
occasionally fed alone or in company with B98-2. Much of the feeding activity was
determined by the boating activity in the marina at any particular time.
The Mollusk
The mollusk
that the Mallard ducks were feeding on was identified as a Banded Mysterysnail, Viviparus
georgianus (Lea, 1834). Dr. Harry Lee of the Florida Museum of Natural History
confirmed the identification and noted that the measurements I provided him were
consistent with the adolescent stage of the mollusk.
The snail specimens that I obtained were small for the range of an adult Viviparus
georgianus. The constant foraging by Mallard ducks could account for the specimens
being smaller than adult size. Occasionally, a duck would bring up a much larger mollusk
that was probably an adult form. Often the bird would have trouble swallowing the snail.
The ducks swallowed the mollusk whole, which was then probably crushed in the bird's
crop. I examined a number of duck feces in the marina area and found that they all
contained shell fragments.
Discussion
From the observations made and the data collected it appears that this behavior is
a learned process that allows Mallard ducks to reside and remain in the Silver Bay, Lake
George, New York area. Without the benefit of marshy or shallow water areas to dabble and
forage for food, the Mallard ducks have had to adapt to an alternative food source. In
this case it is the Banded Mysterysnail, Viviparus georgianus. The snail does
appear to be the primary source of food for the Mallard ducks observed.
The diving Mallard ducks exhibit a classic diving duck style. Stiff-tail for leverage,
an arched back headfirst dive with a kick and push of the feet and legs to achieve total
submersion and downward movement. Their wings remain closed during the dive and they use
their feet effectively to maneuver while underwater.
A first winter male from B98-1 was observed attempting to dabble (dip) in the
traditional Mallard style in some shallow waters of the marina. The bird was not able to
reach the bottom of the lake after a number of attempts. At the time I thought that this
bird may not have learned the diving process and may have been from outside the earlier
observed broods. However, a short time after some surface feeding and insect foraging on
the wharf sides, the bird moved out into deeper water and commenced to dive bringing up
mollusks.
There were several broods of Common Merganser (Mergus merganser) that foraged
for fish and invertebrates along the shoreline of Lake George in the same general area as
the
mallards. The mergansers did not however enter or utilize the marina area. Common
Mergansers were present both years.
There is mention in the literature (Johnsgard, 1968) describing diving behavior in
dabbling ducks. There have also been other individual observations of the diving behavior
in dabbling ducks. Anthony Lang, Ontario, Canada in June 1997 observed a brood of Class II
Mallard ducklings (partly feathered-partly downy) diving near Winnipeg, Manitoba. Peter
Vankevich observed 4 mallard ducks diving in moving water near Roosevelt Island on the
Potomac River in February 1997. Bill Evans, Cornell Lab of Ornithology was astounded to
see a male Mallard dive and stay under for over 3 seconds, then come up with a 4-5 inch
long fish on Cayuga Lake, New York. In late 1980 and early 1990, Michael Price observed
Mallard ducklings repeatedly diving in about 4 feet of freshwater to feed on a carp
carcass in the ponds of Jericho Park, Vancouver, BC.
On further reflection, it should be no surprise to us that the Mallard duck is so
successful and adaptable. After all, all domestic ducks with the exception of the Muscovy
are derived from the Mallard. The Mallard is repeatedly represented in the art of early
cultures and civilizations implying its success at earlier times.
Conclusion
It would be interesting and beneficial to try and locate other Mallard broods on
Lake George and observe to see if a similar behavior exists. The location of other
concentrations of Viviparus georgianus might yield more diving Mallard ducks as
well. A general survey of the protected marinas of Lake George would be a good place to
start.
It would also be beneficial to make observations of adult populations of Lake George
Mallard ducks to examine whether the diving behavior is consistent throughout all
populations and whether or not it is retained as a primary source of foraging in
adulthood. A dispersion study of Mallard ducks throughout the Lake George region might
yield some additional interesting information.