Lesser Scaup

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Image:LesserScaup.JPG

Common Name: Lesser Scaup
Scientific Name: Aythya affinis

Size: 15-19 inches (38-48 cm); Wingspan: 16.4-16.9 inches (41.7-43 cm)

Habitat: The Americas; their breeding habitat is inland lakes and marsh ponds in tundra from Alaska through western Canada to western Montana; few breed east of James Bay and the Great Lakes. Notable breeding concentrations, with more than half a million birds at the height of the season, can be found in Alaska, in the woodlands of the McKenzie River valley and on the Old Crow Flats. These birds migrate south (mostly via the Central and Mississippi Flyways) when the young are fledged and return in early spring, usually arriving on the breeding ground in May. Lesser Scaup typically travel in flocks of 25–50 birds and winter mainly on lakes, rivers and sheltered coastal lagoons and bays between the US–Canadian border and northern Colombia, including Central America, the West Indies and Bermuda.

Wintering Lesser Scaup are typically found in freshwater or slightly brackish habitat and unlike Greater Scaup rarely are seen offshore when unfrozen freshwater habitat is available. They may even spend the winter on lakes in parks, as long as they are not harassed, and will occur even on smallish Caribbean islands such as Grand Cayman. Thousands winter each year on the Topolobampo lagoons in Mexico, and even in the southernmost major wintering location – Ciénaga Grande de Santa Marta in Colombia – where hundreds of birds can be seen. In Central America, flocks are present from July on, but only really numerous after September. They move north again in April and May. In the extreme southeast and southwest of the breeding range – the Rocky Mountains region of the northwestern USA and the southern Great Lakes – Lesser Scaup are present all-year; it is not clear whether the breeding birds are replaced by migrants from the far north in winter, or whether the local populations do not migrate, or whether both local and migrant birds are found there in winter.

Status: Least Concern. Global population: 3,000,000 adult individuals. Although the Lesser Scaup has the largest population of any species of diving duck in North America, their population has been steadily declining since the mid-1980s, and reached an all-time low in the early 20th century. During breeding bird surveys, Lesser and Greater Scaup are counted together due to the impossibility of identifying the species unequivocally when large numbers of birds are involved. Lesser Scaup are thought to comprise slightly less than nine-tenths of the scaup population of North America. In the 1970s, the Lesser Scaup population was estimated at 6.9 million birds on average; in the 1990s it had declined to about half that number, and by the late 2000s it is estimated at 3 million individuals or less. Due to the wide breeding range and the fact that the rate of decline, though remarkable, is still not threatening in respect to the enormous overall numbers, the Lesser Scaup is classified as a Species of Least Concern by the IUCN. An increase of the decline is liable to result in an uplisting to Near Threatened or even Vulnerable status.

The causes for this decline remain unknown. There are indications that the breeding success is decreasing. This may be caused by pollution and habitat destruction, especially in the wintering regions, as well as specific ecological conditions – such as abundance of key food items – which shifted winterwards due to global warming, without the ducks being able to adapt. The Great Scaup, which appears to be increasing in numbers, could be putting the Lesser Scaup under competition for food.

Diet: Small swimming invertebrates and some seeds. They forage by swimming along with bill lowered into the water, straining out small crustaceans and other invertebrates. They do not commonly tip their head and upper body forward into the water.

Nesting: The adult males (drakes) in alternate plumage have a black, effervescent head and a small tuft at the hindcrown, a black breast, a whitish-grey back and wings with darker vermiculations and black outer and greyish-brown inner primary remiges. The underparts are white with some olive vermiculations on the flanks, and the rectrices and tail coverts are black. Adult females (hens) have a white band at the base of the bill, often a lighter ear region, and are otherwise dark brown all over, shading to white on the mid-belly. Drakes in eclipse plumage look similar, but with a very dark head and breast, little or no white on the head and usually some greyish vermiculations on the wings. Immature birds resemble the adult females, but are duller and have hardly any white at the bill base. Both sexes have white secondary remiges, a blue-grey bill with a black "nail" at the tip and grey feet; the drakes have a bright yellow iris, while that of females is orange or amber and that of immatures is brown. Downy hatchlings look much like those of related species, with dark brown upperparts and pale buff underparts, chin, supercilium and back spots.

These birds are not very vocal, at least compared to dabbling ducks. Hens give the namesake discordant scaup, scaup call; in courtship drakes produce weak whistles. Hens vocalize more often than those of the Greater Scaup – particularly during flight –, but their call is weaker, a guttural brrtt, brrtt

They nest in a sheltered location on the ground near water, usually among thick vegetation such as sedges and bulrushes, sometimes in small loose groups and not rarely next to colonies of gulls or terns; several females may deposit eggs in a single nest. The drakes court the hens in the winter quarters; pairs form shortly before and during the spring migration. When nesting starts, the males aggregate while they molt into eclipse plumage, leaving the task of incubation and raising the young to the females alone.

The nest is a shallow depression scraped in the ground and lined with plants and some down feathers. Breeding begins in May, but most birds nest only in June, later than usual for North American waterfowl. The clutch numbers about 9–11 eggs on average; up to 26 eggs have been found in a single nest, but such high numbers are from more than one female. Incubation is by the female only and lasts around 3 weeks. The young fledge some 45–50 days after hatching and soon thereafter the birds migrate to winter quarters. Lesser Scaup become sexually mature in their first or second summer.

About 57% of the Lesser Scaup nests fail each breeding season because the female was killed or the eggs were eaten or destroyed.

Lesser Scaup chicks are capable of diving under water on their hatching day, but they are too buoyant to stay under for more than just a moment. By the time they are 5 to 7 weeks old they are able to dive for 2-25 seconds and swim underwater for 15-18 meters (50-60 ft).

Cool Facts: It is also known as the Little Bluebill or Broadbill because of its distinctive bluish bill. The origin of the name scaup may stem from the bird's preference for feeding on scalp – the Scottish word for oysters, clams, and mussels.

Lesser Scaup are often hard to distinguish from the Greater Scaup when direct comparison is not possible, but in North America a large scaup flock will often have both species present. Females, juveniles and drakes in eclipse plumage are hard to identify; there is considerable overlap in length between the two species, but Greater Scaup are usually noticeably more bulky. Lesser Scaup females and immatures tend to have less white around the bill, but this too varies considerably between individual birds. The bill may give a hint; in the Lesser Scaup it has a stronger curve on the upper side than in the Greater, resulting in a distal part that looks somewhat flattened and wide in the Lesser Scaup – hence the vernacular name "broadbill". If the birds fly, the most tell-tale sign is the white secondary remiges, whereas in the Greater Scaup the white extends on the primary remiges also, i.e. far towards the wingtip.

Habitat is also a key identifier; the Greater Scaup prefers salt water and is found in America and Eurasia, while the Lesser Scaup prefers freshwater and is found only in North America.

An adult Lesser Scaup may pretend to be dead (immobile with head extended, eyes open, and wings held close to body) when grasped by a red fox.

The oldest known individual reached an age of over 18 years.


Found in Songbird Remix Waterfowl Volume II: Diving and Sea Ducks

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