Diving duck trends on Bolinas Lagoon
Diving ducks include medium to large-sized waterbirds with beaks adapted for catching fish or benthic invertebrates and feet placed at the back of their bodies for better propulsion underwater.  This group includes birds that live in a variety of permanent and seasonally aquatic habitats including freshwater lakes, rivers, flooded grasslands, and coastal ecosystems.

For other waterbird trend pages click a link below:

Shorebird trends

Dabbling Duck trends

Grebe trends

Cormorant trends

Heron & Egret trends

Tern trends

Other waterbird trends


For diving duck graphs and profiles click a link below:

Canvasback
Surf Scoter
White-winged Scoter
Common Goldeneye
Bufflehead
Red-breasted Merganser
Ruddy Duck

References

Aythya valisineria

 

Description
The striking male Canvasback, during the breeding season, has a white back, black chest, and rich chestnut-red head and neck.  The bill is long and black and has a gradual slope from head to tip.
 
Range
The majority of Canvasback breed in the prairie lands of southern Canada, but the breeding range extends to Alaska.  During the winter, Canvasback can be found along the western and eastern coasts of the United States and throughout the southern states and Mexico.

Diet
Although the Canvasback eats a wide variety of foods, it specializes in grabbing root stalks, submergent plants, benthic invertebrates, and winter buds from shallow water.

Natural History Facts
The Canvasback prefers to forage in shallow water, but is a competent diver, known to dive up to 9 meters.  Of all ducks in North America, the Canvasback is one of the least abundant.  The small population size is linked to trends of poor breeding success, which are related to lack of food. The diet and foraging method of Canvasbacks make them extremely reliant on the health of stable ponds and marshes.  During a drought or after a habitat disturbance, Canvasback will delay breeding or fail to breed altogether. Changes in availability of food have caused Canvasback to alter their migration patterns, wintering grounds, and diet.

In Point Reyes, the Canvasback is a very rare in the summer and common in the winter.  Canvasback are most abundant on freshwater ponds but can also be found on bays, estuaries, and lagoons.
 
Bolinas Lagoon Population Trends
The number of Canvasbacks on the Bolinas Lagoon has decreased significantly in the past thirty years.  After peaking at 45 birds in 1977, the population rapidly diminished to no birds by 1992.  There have been no Canvasbacks recorded on Bolinas Lagoon since 1992.


Surf Scoter
Melanitta perspicillata

Description
The male Surf Scoter, a large, chunky diving duck is all black with white patches on the head.  Males have a bright white and orange bill; females have a dark bill.  The female is all brown with white smudges on her face.
 
Range
The Surf Scoter breeds from northern Alaska across northern Canada.  It winters along the east and west coast of the United States as well as the west coast of Canada and Alaska.

Diet
During the winter, adults feed primarily on mollusks.  At Bolinas Lagoon, they can frequently be seen eating small crabs.  Surf Scoters will also feed on Herring eggs during spring migration. 

Natural History Notes
In Point Reyes, the Surf Scoter is fairly common in the summer and very common in the winter.  Expect scoters to arrive in the fall from late September or early October through November, with numbers peaking at Bolinas from early November through March.  They frequent inshore waters, bays, estuaries, and on occasion, freshwater ponds.  Scoters will congregate on Tomales Bay in thousands, most likely feeding on Herring eggs, making Tomales Bay an important feeding and staging area for migrating Surf Scoters.  In addition to feeding in open water, Surf Scoters also forage among boulders, rocks, or in sandy areas.
  
Bolinas Lagoon Population Trends
On Bolinas Lagoon, populations peaked during the late 1970s, then suffered a sharp decline. It has remained relatively stable in the past ten years.  

White-winged Scoter
Melanitta fusca

Description
A large, stocky, diving duck, the White-winged Scoter can be identified by the white speculum on each wing.  The male has a comma-shaped white spot around each eye and the female has whitish splotches on her face.  In addition, males have a hump in the middle of their bight orange bill.  Scoters can dive up to 40 feet and must run along the surface of the water to take off.  

Range
The White-winged Scoter winters along the western and eastern coast of the United States, as well as the coasts of Alaska and Canada.  In the spring, they migrate to Canada and central Alaska to breed.   

Diet
This scoter, which feeds almost exclusively by diving, eats mollusks, crustaceans, aquatic insects, and a small amount of aquatic vegetation.
 
Natural History Notes
A common winter resident, the White-winged Scoter arrives at Point Reyes between mid-October and mid-November.  It can be found in bays, estuaries, inshore waters, lagoons, and rarely, freshwater ponds.  White-winged Scoters prefer deeper water than other scoter species and feed over silt, mud, sand, and fine gravel.  In spring, White-winged Scoters migrate over inshore waters in Central California.
   
Bolinas Lagoon Population Trends
The number of White-winged Scoters on the Bolinas Lagoon peaked in 1982 at 32 birds.  The population then decreased to no birds in 1991.  One bird came back to the Lagoon from 1996 to 2002.  Since 2002 there have been no White-winged Scoters found on the Lagoon. 

Common Goldeneye
Bucephala clangula

Description
This medium-sized diving duck is chunky with a large head.  The male is black and white and has a green head with a circular white spot below the eye.  The female has a grayish body and brown head.
                                                                           
Range
Breeds throughout Canada and Alaska in northern boreal forests.  During the winter, the Common Goldeneye resides along the southern coast of Alaska, the western Canadian coast, and throughout the entire United States.

Diet
Dives for aquatic insects, fish, mollusks, and crustaceans in shallow water.  During the winter, they will forage on salt water, in estuaries, and along rocky shorelines.  They are commonly seen eating small crabs on Bolinas Lagoon.

Natural History Facts
During flight, the Common Goldeneye’s wings make a whistling noise, so they are sometimes called “whistlers.”  Aggressive and territorial, the Common Goldeneye is usually dominant over other competing ducks.
   
The Common Goldeneye is a common winter resident and very rare summer visitor at Point Reyes.  The majority of goldeneyes at Point Reyes reside on estuaries, bays, and lagoons, with a few found along the inshore zone and on freshwater ponds and at sewage ponds.
  
Bolinas Lagoon Population Trends
Since 1970, the number of Common Goldeneyes on Bolinas Lagoon has increased from 20 birds to 45 birds in 2004.  However, the population decreased from a peak of 75 birds in 1993 to 45 birds in 2004.

Bufflehead
Bucephala albeola

Description
The smallest diving duck, the attractive breeding male bufflehead is black and white with a large white patch on its head.  The female is mostly brown and white with a small, white oval-shaped cheek patch.

Range
Breeds across Canada and winters throughout most of the United States and northern coastal Mexico.  Its breeding area is confined to boreal forests and the aspen parkland of North America.

Diet
Eats mostly aquatic insects and seeds of aquatic vegetation in fresh and brackish water habitats.  In saltwater habitats, buffleheads eat crustaceans, mollusks, and aquatic vegetation.  During the winter fish play an important role in their diet. 

Natural History Notes
The bufflehead is a rare summer resident and a very common winter resident in Point Reyes.  A number of birds have been observed in summer at Abbott’s Lagoon.  Look for buffleheads in estuaries, bays, lagoons, freshwater ponds and sewage ponds.  They are found in Tomales Bay, Abbott’s and Bolinas Lagoons and Limantour Estero in Point Reyes.

Bolinas Lagoon Population Trends
In 1980, the population peaked at about 270 birds and then fell to 140 birds in 1987.  Since 1987, the Bolinas Lagoon population increased to about 280 birds in 2004.

Red-breasted Merganser
Mergus serrator

Description
This diving duck has a long, pointed, orange bill, crest on back of head and white wing patches visible in flight.  A breeding male has gray sides, a dark reddish-brown chest, white neck ring and a green iridescent head.  Female is dull gray with a shaggy double orange-brown crest. 

Range
Breeds in Alaska and across Canada.  Winters along the east and west coasts of the United States and Canada.

Diet
Eats fish, crustaceans, and aquatic insects.  Some Red-breasted Mergansers are known to fish cooperatively, driving fish into shallow water.  At Bolinas Lagoon they are frequently seen foraging on fish with Double-crested Cormorants.

Natural History Facts
In Point Reyes, the Red-breasted Merganser is a rare summer visitor and a fairly common winter resident.  In the summer, they are most frequently seen at Limantour Estero.  Fall migration extends from October through December and spring migration is from April through May.  They utilize bays, estuaries, lagoons, inshore waters, and occasionally freshwater ponds.  

Bolinas Lagoon Population Trends
The number of wintering Red-breasted Mergansers on Bolinas Lagoon has decreased over the past six years.  The population peaked at 45 birds in 1978 and then remained at around 20-30 birds during the next twenty years.  In the winter of 2004, about 16 were found on the lagoon.   



Ruddy Duck
Oxyura jamaicensis


 
Description
The Ruddy Duck is a small diving duck with a stiff tail (often held up), and white cheek patches.  Breeding males display bright rusty body plumage, black caps, and blue bills.  The female is brownish with a brown line through a white cheek patch. 

Range
The Ruddy Duck breeds throughout the central United States and Canada and winters throughout much of the United States.  It is a year-round resident in parts of the western states and throughout western Mexico. 

Diet
This diving duck obtains its food by straining through soft substrate for insect larvae, aquatic snails and other invertebrates, as well as aquatic vegetation. 

Natural History Notes
An abundant winter resident and fairly common summer resident.  Ruddy Ducks are found primarily on Tomales Bay, Drakes Estero, Bolinas and Abbott’s Lagoon, and freshwater ponds.

Bolinas Lagoon Population Trends
Since 1980, the Ruddy Duck population on Bolinas Lagoon has remained relatively stable, at around 300 birds, until 2000, when the population experienced a sharp decline.  The number of Ruddy Ducks has decreased to about 150 birds in 2004.