With a population decrease of nearly one and one half million in the last 10 years, Lesser Scaup numbers could be cut nearly in half by the end of the decade. Such a drastic reduction has scientists and researchers nationwide working overtime to determine the cause.
The Lesser Scaup, Aythya Affinis, is also called ‘bluebill'. Although not native to North America, Scaup are now found in both hemispheres. Abundant and widespread throughout North America, Lesser Scaup feed by diving for underwater plants and animals. Unlike marsh ducks which feed by tipping their bodies upside down in the water, diving ducks feed by leaping forward and propelling their bodies into deeper water. Because their legs are placed further apart and closer to their tails than marsh ducks, they are awkward on land. Even in water they require a running start across the surface to become airborne.
Lesser Scaup are often difficult to distinguish from their close relative, Greater Scaup. Their markings are quite similar. The males have very light gray bodies with blackish chests, black- appearing heads, distinctive blue bills, and brilliant yellow irises. However, the Lesser male has a higher crown than the Greater. His forehead is steeper. His head is more angular in appearance, and, in the right light, one can distinguish the purple color of his head - in contrast to his relative's green head.
Female Lesser Scaup, as is common in avian families, are much less striking. Their feathers are dark brown with only a small white patch at the base of their bill. Lesser and Greater females both have distinctive blue bills with olive green to brownish yellow irises. The careful observer, however, will note the white stripe on the Lesser's wing, observable only in flight, is shorter than the Greater's white stripe. However, since Lesser Scaup make up more than 90% of the North American Scaup population, around here we are most likely to see Lesser.
Although hard to distinguish by their physical characteristics, their habitat preferences are much more obvious. While Greater Scaup prefer salt water and are found throughout America and Eurasia, Lesser Scaup prefer freshwater and are found only in North America.
The Lesser Scaup's primary breeding grounds are the boreal forests. However, they have also found suitable breeding habitats anywhere from the interior of Alaska to the southern San Francisco Bay. The Centennial Valley is home to several hundred nesting pair even though our numbers have dropped from their high in the late 80's.
Scaup wait until just before reaching their breeding grounds, somewhere between March and May, to pair. Males typically seek older experienced females, but, in the end, the female makes the final decision. Once paired, the female visits several nesting sites before making her final selection.
Their ideal nesting location is situated in shallow water near fresh, well-vegetated wetlands. They will use both permanent and semipermanent bodies of water as well as seasonal wetlands. Dense cattails, bulrushes, pondweeds, or water milfoil, appear to be highly preferred. An adequate food source, consisting of aquatic invertebrates and submerged vegetation, is also necessary.
A Scaup hen begins laying her eggs when the nest is nothing more than a bare scrape on the ground. However, she will continue to add down and grasses to the nest throughout the three to four week incubation period. Scaup eggs are elliptical, nearly oval in shape, and pale green to dark olive in color. The clutch usually ranges from 6 - 14 eggs, however, nesting success rate can be as low as the single digits. According to the Red Rock Lake Wildlife Refuge Biologist, the Centennial enjoys a quite healthy 15 - 30 % success rate.
Once hatched, Scaup chicks can walk, run, swim, and dive almost immediately. However, due to their initial buoyancy, they cannot remain submerged more than a moment or two. Thus, they feed on the surface for the first week. Extremely vulnerable, duckling survival rate during the first ten days is about 40%. Chicks which survive will remain with their mother until they can fly - at about five weeks of age.
Scaup are more carnivorous than other duck species. Their diets include aquatic invertebrates such as amphipods, midges, leeches, clams, and snails. They will also eat fish, especially those which are injured or dead, and fish eggs. Toward summer's end the seeds of aquatic plants, such as pond lilies, often make up the bulk of their diet.
Nearly all their foraging occurs under water. Because Scaup dive diagonally rather than vertically, they submerge and reemerge at different points. These amazing ducks can swim underwater for 2 - 25 seconds and cover 50 - 60 feet in their search for food.
Although Scaup are a potential meal for a variety of carnivores, their most common predator is the Red Fox. In an attempt to foil their captor and escape, Lesser Scaup may pretend to be dead when grasped by a fox. They will hold themselves immobile with their head extended, their eyes closed, and their wings close to their body. In addition to duck predation, unhatched eggs are also vulnerable to being eaten by the common raven.
However, population counts over the last 20 years show the Lesser Scaup species to be facing greater threats than predators. Scientists are still puzzling over the 50% decline this species has experienced in the last 50 years. Prime trouble spots include decreased body condition of breeding females, increased contaminates, and habitat changes in breeding, migration, and wintering areas.
One angle researches are exploring is adult female survival. Some speculate 50% of the annual female mortality occurs during the breeding season. In an effort to curtail this high mortality rate, studies are being conducted on several breeding grounds. These studies have shown the hens are arriving at several breeding grounds in decreased physical condition when compared to earlier studies.
Although this may seem inconsequential, in reality it can have a big effect on the final outcome - chicks. Hens which arrive in poor body condition have to spend more time feeding prior to laying eggs. This results in later nest initiation with the historic outcome being fewer young.
Researchers are seeking to understand the cause. One potential reason is the minnow invasion and introduction into wetlands in the upper Midwest which have possibly resulted in lowering the quality of the Scaup's food. Other possibilities include increased human disturbances resulting in reduced foraging time, increased occurrences of disease, increased instances of parasite invasions, and increases in environmental contaminates.
Still greatly unsubstantiated, researchers are leaning more strongly toward the impact of environmental contaminants as a primary reason. Zebra mussels, fairly new residents of the Great Lakes and the Illinois and Mississippi River systems, are highly suspect. Introduced into US waters in the mid 80's, Zebra mussels have traditionally been a food source for European diving ducks. In America, however, before the introduction of these mussels, molluscs only represented 30% of the American diving duck's spring and fall diet. Today they represent nearly 100%.
Although the mollusc ingestion creates no danger in and of itself, being filter feeders, Zebra muscles are completely non-selective in their feeding methods. In addition, they have high reproductive potentials resulting in high densities in several areas. Since they accumulate water- associated pollutants at higher rates than the native bivalves, they have become a potentially dangerous contamination source.
To more accurately access the danger, scientists experimented feeding contaminated Zebra mussels to captive Tufted Ducks. It should be noted, these mussels possessed contaminates similar to those in wild Zebra mussels. Test results showed negative changes in the ducks' livers and kidneys. The birds' suffered from behavioral deviations, fewer and smaller eggs, reduced hatching rates, lower chick rates, and higher female mortality.
The primary contaminate worrying scientists is Selenium. A natural occurring trace mineral, Selenium is also an industrial by-product. Although nutritionally required in small amounts, it is considered highly toxic in slightly accelerated amounts. Selenium concentrations build up quickly in the tissues with high levels affecting reproduction and possibly survival.
After spring testing Lesser and Greater Scaup in the lower Great Lakes, scientists discovered abnormally high trace mineral levels. Because Selenium input into the lower Great Lakes has not increased substantially over the past 15 years, scientists attribute this increase to the bird's escalated Zebra mussel consumption.
The final area scientists are exploring is habitat change. Whether we're talking breeding habitat or migration habitat, there is no denying changes are occurring. Whether these changes are harmful to the birds, or not, is still a matter of investigation.
Northwest Canada and Alaska's Boreal Forest makes up 60% of the Lesser Scaup breeding grounds. Aspens, spruce, and wetlands interlace to create this unique landscape. Since the birds are so heavily dependent on these areas for breeding, some fear changes to the Boreal Forest could drastically affect their future.
Changes currently (and traditionally) occurring within the Boreal forest include logging, fire, agriculture, acid rain, and oil and gas developments. Logging operations have recently been under attack. However, studies have shown the trees in the Boreal forest do not live longer than 100 - 150 years. Since the forest thrives on disturbance, logging, properly conducted, may actually be beneficial. Currently regulations are in effect in most areas requiring logging firms to minimize negative environmental impact by replanting, putting roads to bed, minimizing erosion, and minimizing disturbances to watersheds.
Agricultural changes, however, may not be so easy to minimize. As we lose agricultural grounds across North America, Boreal forest soils may be in greater demand for their food producing potential. However, once cleared for grain fields or pasture, the trees do not grow back unless they are replanted.
Scientists are also studying oil and gas developments occurring in the Boreal Forests. Each oil pump or gas well requires a five-acre pad, cleared of trees and drained of wetlands. In addition, the total picture includes pipe lines and oil spills. Fortunately, most oil and gas developments are occurring south of the prime forests.
Another habitat region creating concerns is San Francisco Bay. A primary winter destination for Scaup, this bay teems with crustaceans and mollusks, including a new non-native mussel. Unfortunately, Selenium pours into the bay from refineries along the eastern shore as well as from the San Joaquin River. Additionally, gasoline and oil spill remnants find their way into the bay's water. Mercury, Cadmium, Zinc, and Copper also flow into the bay. These contaminates end up in mollusks and fish, and perhaps in the ducks that eat them. If so, these pollutants can cause reduced carcass fat and reduced pancreas size, resulting in poor condition when the birds return their breeding grounds.
The final habitat region under consideration is the Mississippi River system. A highly used habitat during migration, the upper Mississippi is a diverse array of wetlands, open waters, and flood plains. However, this watershed is intensely cultivated filling many tributary streams with substantial loads of nutrients, pesticides, and sediments. These stream loads are believed to be contributing to the decline of several traditional Scaup food sources including: fingernail clams, unionid mussel fauna, and submersed aquatic plants.
Obviously there are no easy solutions. Researchers have no well-developed answers, but believe several factors are contributing to the problem. Except for the Zebra mussels, every issue being looked at involves human practices. As always it behooves us to think ‘stewardship' as we seek to stymie the Scaup's rapid decline. Obviously these birds are important to the ecosystem. However, so are humans. Therefore, any solution will likely require greater restraint and caution on our part, increased correction of improper usages, and balanced natural resource management which will be beneficial to both humans and all other living creatures.
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