BIOLOGICAL DATA AND HABITAT REQUIREMENTS
WILDLIFE SPECIES: Aythya valisineria | Canvasback 



TIMING OF MAJOR LIFE HISTORY EVENTS : 
Pair bonding - Canvasback pair bonding takes place in late winter.  Most
canvasbacks arrive on their breeding grounds already paired [12].

Nesting - Canvasbacks begin to nest in late April or early May [1].
Even in the subarctic, canvasbacks nest almost as early as in the
northern prairies [1].  The nesting season generally lasts from April to
June [1,12].

Clutch size/incubation - Determining the clutch size in canvasback nests
is complicated by the effect of redhead (Aythya americana) parasitism on
the number of host eggs.  When redheads lay in canvasback nests, host
clutches are reduced in size.  Clutches usually consist of 7 to 12 eggs
and average 9 1/2 in nonparasitized nests.  Clutches are somewhat
smaller in parasitized nests [1,8].  Female canvasbacks seldom lay eggs
in the nests of other species but commonly parasitize the nests of other
canvasback hens [1].

The incubation period normally lasts about 24 days but sometimes as long
as 29 days [7,8].  The inclusion of eggs laid by other females sometimes
results in several unhatched eggs being left in the nest at the time of
general hatching [8].

Fledging - Fledging requires about 56 to 68 days [8].

Age at sexual maturity - Canvasbacks become sexually mature their first
winter [7,8].

Molting - Drakes begin to gather on molting grounds shortly after
females start incubation.  Most have completed their prenuptual molt by
mid-October or early November.  Hens begin to molt after leaving their
broods in the fall [7].

Migration/Fall - Canvasbacks begin to migrate into the Northern Great
Plains in early September.  Numbers slowly build up to late October,
followed by rapid departures in early November.  Canvasbacks in the east
arrive in the Great Lakes States in early October, reach peak numbers by
early November, and decline rapidly to wintering numbers by the end of
the month.  Canvasbacks arrive on their winter grounds adjacent to the
central Gulf Coast in late November.  Farther south on the lower Texas
coast, however, they arrive almost a month earlier [1].  They arrive on
winter grounds in central California in late October, and numbers
steadily increase through November and December.  On winter grounds in
southern California, canvasbacks do not appear until late November and
rapidly increase in numbers through December [1].

Migration/spring - Canvasbacks begin departing many of their winter
areas in early February.  On most winter areas, there is a steady
departure lasting almost to mid-April.  On lakes midway to their
breeding grounds, canvasbacks appear in small numbers in late February,
with populations rapidly increasing through March.  Canvasbacks begin to
arrive on the southern margins of their breeding grounds in the Great
Plains in early April [1].


PREFERRED HABITAT : 
Breeding/nesting habitat - Canvasbacks breed and nest on large marshes,
ponds, sloughs, and potholes [1].  Pairs occupy the larger, deeper ponds
for feeding, resting, and courting but use the smaller, shallower ponds
for nesting.  These ponds are usually less than an acre and are
encircled by bands of cattails and bulrushes.  Brood ponds are
intermediate in size between those used for feeding and for nesting but
contain considerable marsh vegetation [1].

Canvasbacks usually nest over water 6 to 24 inches (15-60 cm) deep
[1,3].  They sometimes build their nests on muskrat houses and rarely on
dry ground.  They attach the nest to surrounding plants or build it on a
mat of floating dead plants, generally 3 to 60 feet (0.9-18.3 m) from
the edge of open water [3,7].

Migration and winter habitat - Large lakes of 150 acres (61 ha) or more,
marshes, and rivers with submerged beds of pondweed are favored during
migration.  Canvasbacks winter primarily on estuaries, sheltered bays,
coastal lagoons, and sometimes on deep freshwater lakes [3,8].


COVER REQUIREMENTS : 
Canvasbacks select stands of emergent vegetation for nesting cover [7].
Canvasback broods seek the most open, the largest, and the deepest
potholes for their development [1].


FOOD HABITS : 
Canvasbacks dive in shallow water, usually 3 to 12 feet (0.9-3.6 m)
deep, for food.  Their diet generally consists of about 80 percent
vegetative matter [3].  In the northeastern United States, canvasbacks
prefer seeds and vegetative parts of wild celery; in the Southeast and
the West they primarily consume pondweeds.  They also feed on bulrush
seeds, widgeongrass, eelgrass, arrowhead (Sagittaria spp.) and coontail
(Ceratophyllum demersum).  Animal matter consumed by canvasbacks mostly
consists of mollusks, insects, fish, and mud crabs [1,3,10].

Management of food resources on canvasback staging areas must emphasize
wild celery and other plants that produce tubers, such as arrowhead and
pondweeds [10].


PREDATORS : 
The heaviest nest destruction by predators commonly occurs during the
egg-laying period when the hen is off the nest [7].  Raccoons are the
most common predators of canvasback nests.  In 1973 one study reported
that this predator was responsible for 60 percent of all canvasback
nests destroyed in the Minnesota potholes in Manitoba [1].  Skunks are
the second most important mammalian predator of canvasback nests in the
prairie breeding grounds.  They are especially destructive in years when
water recedes from marginal marsh cover, leaving nests stranded on dry
ground, or when low water at the beginning of the nesting season
necessitates placing nests out of the water.  Coyotes, foxes, minks,
weasels, crows, and magpies also prey upon canvasback nests [1].
Additionally coyotes, foxes, minks, and weasels prey on ducklings and
adults.


MANAGEMENT CONSIDERATIONS : 
Of all the extensively distributed game ducks in North America, the
canvasback is the least abundant [1].  The canvasback population has
decreased due to habitat loss and overhunting [8].  In the 1930's the
population decreased after a series of drought years prevented any
reasonable breeding success.  During the 1960's and 1970's the extensive
drainage of prairie marshes resulted in a decline in canvasbacks to an
estimated 500,000 individuals by the mid 1970's; a 50 percent reduction
of numbers estimated 20 years earlier.  Canvasbacks have also been lost
due to oil spills in key wintering areas [12].  Current population
numbers were not found in the literature.

Desertion of canvasback nests is a far greater problem than in most
other waterfowl species.  Hens desert their nest because of flooding or
brood parasitism by redheads and other canvasbacks.  Heavy rains on
small potholes or wind tides on large marshes often raise the water
faster than the hens are able to build up the nest platforms [1].


REFERENCES : 
NO-ENTRY

Related categories for Wildlife Species: Aythya valisineria | Canvasback