Aythya collarisring-necked duck

Geographic Range

Ring-necked ducks are mainly a migratory species. During the breeding season, it can be found as far north as southern and central Alaska. Other populated portions of North America include the central Canadian regions as well as Minnesota, Maine, and some smaller portions of the northern United States. A few areas, including parts of Washington, Idaho, and other central western states of the United States are home to ring-necked ducks year-round. The species nests most often in the northern regions of Alberta, Saskatchewan, Minnesota, Wisconsin, Michigan, the central regions of Manitoba, and the southern regions of Ontario and Quebec.

These ducks prefer to spend their winters in the southern regions of New England and the Great Plains in the United States, the southern regions of British Columbia in Canada, and areas farther south including Mexico, Costa Rica, Jamaica, and Puerto Rico. During the winter, small numbers have been found in Venezuela and Trinidad. Small numbers have also been recorded in Panama, Bermuda, the Bahamas, Cuba, and the Dominican Republic.

This species is a vagrant in the north African countries of Algeria and Morocco, Japan, and the European nations of Austria, Belgium, Denmark, Faroe Islands, Finland, France, Germany, Iceland, Ireland, the Netherlands, Norway, Poland, Portugal, Spain, Sweden, Switzerland, and the United Kingdom. ("Aythya collaris", 2009; Hohman and Eberhardt, 1998)

Habitat

The habitat of Aythya collaris varies seasonally. During the breeding and post-breeding season the species prefers freshwater wetlands, usually fens, bogs, and marshes, all of which are quite shallow. The pH of these wetlands is usually near neutral because the aquatic invertebrates these ducks, especially females during the breeding season, consume do not fair well under highly acidic conditions. Areas commonly inhabited have a high level of organic material within. There is usually abundant vegetation, both floating and submerged, with open water zones found throughout as well.

During the winter, the species utilizes a huge array of wetlands, but is rarely found in areas with high salinity levels or depths >1.5 meters. Floodplains of rivers, fresh and brackish parts of estuaries, and shallow inland lakes and marshes are common habitats. These shallow areas are also rich with moist soil vegetation. Aythya collaris has also been found in flooded agricultural lands, aquaculture ponds, and managed freshwater impoundments.

When nesting, ring-necked ducks prefer to live in smaller, shallower wetlands. Because these areas are relatively more abundant than the large open waters preferred by several other duck species, Aythya collaris often has a relatively higher rate of nesting success compared to those species. (Bendell and McNicol, 1995; Hohman and Eberhardt, 1998; Maxson and Riggs, 1996)

Physical Description

Ring-necked ducks are small to medium in size. Males are slightly larger than females. Total length of males falls between 40 and 46 cm, and between 39 and 43 cm for females. The mass of males falls between 542 and 910 g and in females is usually between 490 and 894 g. Seasonal body mass fluctuations are common and cause overlaps between the sexes. Ring-necked ducks have a wingspan of 63.5 cm.

Defining characteristics of adult males include a black head, neck, breast, and upper portions, with a whitish gray belly and flanks. On the folded wing is a distinct white wedge on the shoulder that extends upwards. Adult females are grayish brown, with the darkest coloration on top of the head. They are pale on the front of their heads, chins, and throats. Eyes are bordered by a white ring, and females appear overall duller than males. The species is similar in profile to other diving ducks, but with a tail that is somewhat longer and a head that contains a short crest, which gives it its distinct peaked or angular appearance. Immature Aythya collaris appear similar to the adults, but are more dull in coloration.

In the winter, adults and ducklings experience changes in physical appearance. The body mass of both increases, but adults show a more drastic change from their original mass. (Hohman and Eberhardt, 1998; Hohman and Weller, 1994)

  • Sexual Dimorphism
  • male larger
  • sexes colored or patterned differently
  • male more colorful
  • Range mass
    490 to 910 g
    17.27 to 32.07 oz
  • Range length
    39 to 46 cm
    15.35 to 18.11 in
  • Average wingspan
    63.5 cm
    25.00 in

Reproduction

Aythya collaris is a primarily monogamous species that forms pair bonds. This occurs during spring migration, from March until April.

Reproductive behaviors are similar to that of other species of diving birds and include mutual displays. An example of this includes a neck stretch, in which the head is raised to full neck extension with the bill pointed forward and slightly elevated. This behavior can occur both in or out of the water. Drinking or bill-dipping, in which the bill is lowered into the water without raising the head, and post-copulatory swimming, where the male and female swim side by side with heads held high, are two other examples of mutual mating displays.

Male only displays include a head throw (the head is brought back until the throat is part vertical), nod swimming (a rapid swim while the head nods back and forth with the crest fully extended) and preening behind the wing (the preening of the scapular region with the wing partially extended).

Extra-pair copulations are very uncommon but have been seen in northwestern Minnesota during a drought year. This happened at a time when the body masses of returning birds, food availability, and breeding participation of the females were much lower than they had been in previous years. (Hohman and Eberhardt, 1998)

The breeding season of ring-necked ducks occurs between the months of May and early August, with peak activity from mid-May until mid-July. Pair bonds are formed during spring migration and remain until late June or early July.

In selecting a site for nesting, pairs swim along the open waters of wetlands. The females swim into flooded vegetation looking for suitable sites, while the male keeps lookout nearby. They search for a dry or semidry site situated near water, often with clumps of vegetation. The female constructs the nest. After 3 to 4 days of nest building, the nest resembles a bowl, and by day 6 the nest is strong with a clear shape to it. Occasionally nest construction doesn't begin until the 3rd or 4th egg is laid. Nests are lined with bent grasses and downy feathers.

Female ring-necked ducks lay between 6 and 14 eggs per season, with an average between 8 and 10. The eggs are ovular in shape and range in color from olive-gray to olive-brown, possessing a smooth surface texture. Incubation starts after the clutch is completed, and the beginning of incubation is the first day the female remains at the nest overnight. Incubation generally lasts 26 or 27 days. The precocial chicks hatch weighing between 28 and 31 g. Chicks are covered in downy feathers and are capable of following parents and feeding themselves soon after hatching. Young fledge after 49 to 56 days and reach independence 21 to 56 days after fledging. Reproductive maturity is achieved quite quickly in both sexes, with both breeding in their first year, although young ducks may shy away from breeding some years due to lower availability of nesting areas. (Hohman and Eberhardt, 1998; Hohman, 1986)

  • Breeding interval
    Ring-necked ducks produce one brood per season, but may produce another clutch if initial nest is destroyed.
  • Breeding season
    Ring-necked ducks breed from May to early August (peak activity from mid-May until mid-July).
  • Range eggs per season
    6 to 14
  • Average eggs per season
    8 to 10
  • Average eggs per season
    9
    AnAge
  • Range time to hatching
    25 to 29 days
  • Average time to hatching
    26 to 27 days
  • Range fledging age
    49 to 56 days
  • Range time to independence
    21 to 56 days
  • Average age at sexual or reproductive maturity (female)
    1 years
  • Average age at sexual or reproductive maturity (male)
    1 years

Parental care of offspring is exhibited by females only, but males aid indirectly in the production of offspring by attending to the nutritional needs of their mates while they are in the laying stage of reproduction. The young emerge from the egg without their mother's aid, after which she crushes the shells and proceeds to bury them, carrying them away from the nest, or ingesting them. Aythya collaris young gain the ability to dive about 48 hours post hatching, but count on surface foods mostly for the first week of life, and do not count on their mothers to feed them.

The mother generally remains with the young until fledging, but sometimes leaves earlier if the young have begun to develop the contour feathers necessary for flight. Maternal care is mostly protective. After the mother leaves, broods have been shown to spend more time feeding and less time resting, probably due to the loss of the mother's vigilant eye. (Hohman and Eberhardt, 1998; Hohman, 1986)

  • Parental Investment
  • precocial
  • female parental care
  • pre-fertilization
    • provisioning
    • protecting
      • male
      • female
  • pre-hatching/birth
    • provisioning
      • female
    • protecting
      • female
  • pre-weaning/fledging
    • protecting
      • female
  • pre-independence
    • protecting
      • female

Lifespan/Longevity

Using estimates from band recoveries, it has been shown that the annual survival rates of male ring-necked ducks is greater than that of the females, 63-69% versus 48-58% respectively. A possible hypothesis for this is that females alone practice parental behavior are therefore put in dangerous positions when having to defend their young, as well as themselves, from predators. The oldest banded ring-necked duck was recovered twenty years after banding, and given an age estimate of just over 20 years. (Hohman and Eberhardt, 1998)

Behavior

Ring-necked ducks are a highly motile species that moves by walking, hopping, flying, swimming, and diving. It leaves the water to stand on floating objects for rest or comfort, and during nesting. The flight of this species is swift and flocks of twenty or less fly together in dense wedges. In comparison to other members of the genus Aythya, ring-necked ducks appear to exhibit more buoyancy during swimming. The duck can dive to depths of up to ten meters using foot propulsion. These ducks also perform self-maintenance in the form of preening, head-scratching, stretching, and bathing. While resting or sunbathing, the bird is found usually in calm, open water sheltered from the wind.

Time budgets per activity vary between the sexes and age groups. Feeding is the dominant activity of nesting females, with up to 19 hours per day spent feeding while laying eggs and 57% of the time during incubation. In Minnesota, ducklings spent 41% of their time feeding, 31% resting, and 21% participating in leisure activities. Time-activity budgets also depend upon the habitat occupied. For example, one study found that members of this species that migrated to Texan reservoirs that experienced heavy boat traffic spent much more of their time in locomotion, moving away from boats. During the winter months, the time budgets of the sexes are more similar than they are during other time periods, with feeding taking up about 20 to 55% of the day and resting 14 to 43%. Courtship and aggression during winter are rare.

The hierarchy present within Aythya collaris is as follows: Male adult dominant to female adult and adult dominant to immature duckling. There is no evidence of territoriality, but in open water a paired male defends a radius of 2 to 3 meters around his mate. The ducks are least social when they are paired off or while taking care of young. All females obtain a mate at the breeding ground but because of a skewed sex ratio (males outnumber females 1.6:1), some males remain solitary and may choose to associate in small groups of 6 or less. During the non-breeding seasons, ring-necked ducks are usually associated with flocks of 40 birds or less. During migratory periods and winter, if food and resources are plentiful, flocks may reach greater than 10,000 individuals.

Ring-necked ducks can exhibit molting throughout the majority of the year. The highest levels of molting have been found to be during April-May, July-September, and December-January, while the lowest levels have been observed in March. Molting is related to seasonal change, and is in preparation of the spring and fall migrations. Spring migration occurs from February to May, with peak levels during March and April. Fall migration occurs from September to December, with peak levels during October and November. (Crook, et al., 2009; Hohman and Crawford, 1995; Hohman and Eberhardt, 1998)

  • Range territory size
    2 to 3 m^2

Home Range

There is no evidence of territoriality, but in open water a paired male defends a radius of 2 to 3 meters around his mate.

Communication and Perception

Aythya collaris is a vocal animal, but these vocalizations have not been studied in depth. The male "kink-neck" call is emitted during the courtship displays of neck stretching and head throwing. During courtship displays or when curious, the female makes a soft purring growl. When alarmed or during flight in the nesting season, the female may make a high pitched growl. Alarm calls given to a brood by the mother are short and soft 'cut-cut-cut' noises.

Ring-necked ducks rely heavily on visual communication during courtship displays. Males attract mates through various displays including neck stretching, head throwing, and nod swimming. Females respond to these displays using head bobbing. Successfully paired mates perform post-copulatory swimming, where the male and female swim side by side with heads held high. Like all birds, ring-necked ducks perceive their environments through visual, auditory, tactile and chemical stimuli. (Hohman and Eberhardt, 1998)

  • Other Communication Modes
  • duets

Food Habits

In winter, shallow bodies of water such as flood plains and the margins of lakes and bogs are filled and plants requiring moist soils or that float on the water's surface abound. Spring migrants locate food in these flooded areas. Members of this species eat mainly plant seeds and tubers from the moist soil and feed on aquatic invertebrates as well. Occasionally they prey on insects. Nesting adults and offspring forage on aquatic plant species like pondweed, coontail, cow lily, and water milfoil. Fall migrants obtain food from shallow lakes and rivers that have wild rice, American wild celery, or arrowheads.

Aythya collaris feeds mainly by shallow diving, but also collecting items on or near the surface of the water. Its preference for obtaining food from shallow waters, even though it can dive, can be attributed to the high level of biomass closer to the surface. This species is more of an opportunistic and generalized feeder than others in the same genus. The species usually consumes food during dives, but some food is brought back to the surface to be processed, such as removing food from the shell of gastropods and removing protective layers from insects.

Prey ranges in size from less than 0.1 mm to 5 cm. Invertebrate consumption is the greatest in young, and composes 98% of the total diet. Females tend to eat more invertebrates than usual during the breeding season, a time when more dietary protein is necessary. The males sometimes exhibit slight increases in invertebrate consumption, but the change is not as significant as in females. Some common prey of ring-necked ducks includes aquatic earthworms, snails, clams, dragonflies, and caddis flies. (Alisauskas, et al., 1990; Eberhardt and Riggs, 1995; Hohman and Eberhardt, 1998; Olsen and Perry, 1997; Torrence and Butler, 2006)

  • Animal Foods
  • insects
  • mollusks
  • terrestrial worms
  • aquatic or marine worms
  • aquatic crustaceans
  • Plant Foods
  • leaves
  • roots and tubers
  • seeds, grains, and nuts

Predation

In Maine, examples of predators on adult Aythya collaris include red fox, raccoons, Northern harriers, great horned owls, American mink, bald eagles, peregrine falcons, and common snapping turtles. There are also many organisms which prey on the eggs of ring-necked ducks, major predators include American mink, crows, ravens, raccoons, fox, muskrat, skunks, and domestic dogs. Ducklings may fall prey to large, predatory fish such as pike and bass.

In order to prevent predation at the nest, some females will defecate on eggs to cover their enticing scent. Some ducks fake injury when disturbed. When broods are attacked from below the water, the mother uses her wings and feet to attack while the ducklings scatter away. Adults and young use their diving ability to try and escape aerial predation. (Hohman and Eberhardt, 1998)

Ecosystem Roles

Aythya collaris serves as a host to parasites Clostridium botulinum and Pasteurella multocida, which cause avian botulism and avian cholera, respectively. The parasites are most prevalent in California, but have been found to cause botulism and cholera throughout the Pacific, central, and Mississippi waterways. Bacterial diseases which cause mortality in these ducks include coccidiosis, aspergillosis, and avian tuberculosis. Ring-necked ducks can be infected by a wide array of parasites.

Ring-necked ducks are both herbivores and predators on aquatic invertebrates and have a significant impact on those populations where they forage. Eggs, young, and adult ring-necked ducks are a source of food for many predators. (Hohman and Eberhardt, 1998)

Commensal/Parasitic Species
  • Avian botulism (Clostridium botulinum)
  • Avian cholera (Pasteurella multocida)

Economic Importance for Humans: Positive

Ring-necked ducks are economically important in the hunting and game industry. They are widely hunted across Canada and the United States. (Hohman and Eberhardt, 1998)

Economic Importance for Humans: Negative

There is no direct negative effect on humans but because of the lead some ducks swallow due to human hunting (before the switch to nontoxic pellets) the possibility for biomagnification exists. That is, if this species ingests lead shot, and is then eaten by another organism such as a bass or pike, the next higher predator to consume the bass or pike is going to get a larger dosage of lead in their system. This higher organism could be an eagle or falcon, but could very well be a human being. (Hohman and Eberhardt, 1998)

Conservation Status

This species has an extremely large range and is not declining or fluctuating in population size. Ring-necked duck habitats are currently healthy and abundant. The species is considered by the IUCN Red List to be of least concern. However, lead poisoning is common in some areas due to the ingestion of lead pellets used by hunters. In 1991 the United States called for a mandatory switch to non-toxic shot made of steel or bismuth and tin. A study done in 1996 of the Mississippi waterways found that 12.7% of 749 ring-necked ducks surveyed contained the non-toxic pellets, and of those 55% ingested both non-toxic and lead forms at some point. Also, there is a huge threat to ducklings, as they spend the majority of their time foraging, that may ingest lead as well as nontoxic pellets. Lead levels continue to be a problem years after the switch. Also, these ducks are hunted in other countries that still permit the use of lead shot.

The acidification of habitats can kill off the invertebrates Ayatha collaris relies on heavily during the breeding season. The potential adverse effects of this have not been studied in depth. ("Aythya collaris", 2009; Anderson, et al., 2000; McCracken, et al., 2000)

Contributors

Shahina Patel (author), University of Michigan-Ann Arbor, Phil Myers (editor), University of Michigan-Ann Arbor, Rachelle Sterling (editor), Special Projects.

Glossary

Nearctic

living in the Nearctic biogeographic province, the northern part of the New World. This includes Greenland, the Canadian Arctic islands, and all of the North American as far south as the highlands of central Mexico.

World Map

Neotropical

living in the southern part of the New World. In other words, Central and South America.

World Map

acoustic

uses sound to communicate

agricultural

living in landscapes dominated by human agriculture.

bilateral symmetry

having body symmetry such that the animal can be divided in one plane into two mirror-image halves. Animals with bilateral symmetry have dorsal and ventral sides, as well as anterior and posterior ends. Synapomorphy of the Bilateria.

bog

a wetland area rich in accumulated plant material and with acidic soils surrounding a body of open water. Bogs have a flora dominated by sedges, heaths, and sphagnum.

brackish water

areas with salty water, usually in coastal marshes and estuaries.

chemical

uses smells or other chemicals to communicate

coastal

the nearshore aquatic habitats near a coast, or shoreline.

diurnal
  1. active during the day, 2. lasting for one day.
duets

to jointly display, usually with sounds in a highly coordinated fashion, at the same time as one other individual of the same species, often a mate

endothermic

animals that use metabolically generated heat to regulate body temperature independently of ambient temperature. Endothermy is a synapomorphy of the Mammalia, although it may have arisen in a (now extinct) synapsid ancestor; the fossil record does not distinguish these possibilities. Convergent in birds.

estuarine

an area where a freshwater river meets the ocean and tidal influences result in fluctuations in salinity.

female parental care

parental care is carried out by females

fertilization

union of egg and spermatozoan

folivore

an animal that mainly eats leaves.

freshwater

mainly lives in water that is not salty.

herbivore

An animal that eats mainly plants or parts of plants.

iteroparous

offspring are produced in more than one group (litters, clutches, etc.) and across multiple seasons (or other periods hospitable to reproduction). Iteroparous animals must, by definition, survive over multiple seasons (or periodic condition changes).

marsh

marshes are wetland areas often dominated by grasses and reeds.

migratory

makes seasonal movements between breeding and wintering grounds

monogamous

Having one mate at a time.

motile

having the capacity to move from one place to another.

natatorial

specialized for swimming

native range

the area in which the animal is naturally found, the region in which it is endemic.

oviparous

reproduction in which eggs are released by the female; development of offspring occurs outside the mother's body.

riparian

Referring to something living or located adjacent to a waterbody (usually, but not always, a river or stream).

seasonal breeding

breeding is confined to a particular season

sexual

reproduction that includes combining the genetic contribution of two individuals, a male and a female

social

associates with others of its species; forms social groups.

solitary

lives alone

tactile

uses touch to communicate

temperate

that region of the Earth between 23.5 degrees North and 60 degrees North (between the Tropic of Cancer and the Arctic Circle) and between 23.5 degrees South and 60 degrees South (between the Tropic of Capricorn and the Antarctic Circle).

terrestrial

Living on the ground.

tropical

the region of the earth that surrounds the equator, from 23.5 degrees north to 23.5 degrees south.

tropical savanna and grassland

A terrestrial biome. Savannas are grasslands with scattered individual trees that do not form a closed canopy. Extensive savannas are found in parts of subtropical and tropical Africa and South America, and in Australia.

savanna

A grassland with scattered trees or scattered clumps of trees, a type of community intermediate between grassland and forest. See also Tropical savanna and grassland biome.

temperate grassland

A terrestrial biome found in temperate latitudes (>23.5? N or S latitude). Vegetation is made up mostly of grasses, the height and species diversity of which depend largely on the amount of moisture available. Fire and grazing are important in the long-term maintenance of grasslands.

visual

uses sight to communicate

young precocial

young are relatively well-developed when born

References

2009. "Aythya collaris" (On-line). Red List. Accessed March 20, 2010 at http://www.iucnredlist.org/apps/redlist/details/141543/0.

Alisauskas, R., R. Eberhardt, C. Ankney. 1990. Nutrient reserves of breeding Ring-necked Ducks (Aythya collaris). Canadian Journal of Zoology, 68(12): 2524-2530. Accessed April 13, 2010 at http://rparticle.web-p.cisti.nrc.ca/rparticle/AbstractTemplateServlet?journal=cjz&volume=68&year=1990&issue=68&msno=z90-353&calyLang=eng.

Anderson, W., S. Havera, B. Zercher. 2000. Ingestion of Lead and Nontoxic Shotgun Pellets by Ducks in the Mississippi Flyway. The Journal of Wildlife Management, 64(3): 848-857. Accessed April 16, 2010 at http://www.jstor.org/sici?sici=0022-541X%28200007%2964%3A3%3C848%3AIOLANS%3E2.0.CO%3B2-C&origin=ISI&cookieSet=1.

Bendell, B., D. McNicol. 1995. The diet of insectivorous ducklings and the acidification of small Ontario lakes. Canadian Journal of Zoology, 73(11): 2044–2051. Accessed March 20, 2010 at http://rparticle.web-p.cisti.nrc.ca.proxy.lib.umich.edu/rparticle/AbstractTemplateServlet?journal=cjz&volume=73&year=1995&issue=73&msno=z95-240&calyLang=eng.

Crook, S., W. Conway, C. Mason, K. Kraai. 2009. Winter Time-Activity Budgets of Diving Ducks on Eastern Texas Reservoirs. Waterbirds, 32(4): 548-558. Accessed April 13, 2010 at http://www.bioone.org/doi/full/10.1675/063.032.0408.

Eberhardt, R., M. Riggs. 1995. Effects of sex and reproductive status on the diets of breeding Ring-necked Ducks (Aythya collaris) in north-central Minnesota. Canadian Journal of Zoology, 73(2): 392–399. Accessed March 20, 2010 at http://rparticle.web-p.cisti.nrc.ca.proxy.lib.umich.edu/rparticle/AbstractTemplateServlet?journal=cjz&volume=73&year=1995&issue=73&msno=z95-043&calyLang=eng.

Hohman, W. 1986. Changes in Body Weight and Body Composition of Breeding Ring-Necked Ducks (Aythya collaris). The Auk, 103(1): 181-188. Accessed April 13, 2010 at http://www.jstor.org/stable/pdfplus/4086978.pdf.

Hohman, W., R. Crawford. 1995. Molt in the Annual Cycle of Ring-Necked Ducks. The Condor, 97(2): 473-483. Accessed March 20, 2010 at http://www.jstor.org.proxy.lib.umich.edu/sici?origin=sfx%3Asfx&sici=0010-5422(199505)97%3A2%3C473%3AMITACO%3E2.0.CO%3B2-L.

Hohman, W., R. Eberhardt. 1998. "The Birds of North America Online" (On-line). The Birds of North America Online. Accessed March 09, 2010 at http://bna.birds.cornell.edu.proxy.lib.umich.edu/bna/species/329/articles/introduction.

Hohman, W., M. Weller. 1994. Body Mass and Composition of Ring-Necked Ducks Wintering in Southern Florida. The Wilson Bulletin, 106(3): 494-507. Accessed March 20, 2010 at http://www.jstor.org.proxy.lib.umich.edu/sici?origin=sfx%3Asfx&sici=0043-5643(199409)106%3A3%3C494%3ABMACOR%3E2.0.CO%3B2-P.

Maxson, S., M. Riggs. 1996. Habitat Use and Nest Success of Overwater Nesting Ducks in Westcentral Minnesota. The Journal of Wildlife Management, 60(1): 108-119. Accessed April 13, 2010 at http://www.jstor.org/sici?sici=0022-541X%28199601%2960%3A1%3C108%3AHUANSO%3E2.0.CO%3B2-1&origin=ISI.

McCracken, K., A. Afton, M. Peters. 2000. Condition bias of hunter-shot ring-necked ducks exposed to lead. Journal of Wildlife Management, 64(2): 584-590. Accessed April 13, 2010 at http://www.jstor.org/stable/3803256?seq=1.

Noseworthy, S., W. Threlfall. 1978. Some Metazoan Parasites of Ring-Necked Ducks, Aythya collaris (Donovan), from Canada. The Journal of Parasitology, 64(2): 365-367. Accessed March 20, 2010 at http://www.jstor.org.proxy.lib.umich.edu/sici?origin=sfx%3Asfx&sici=0022-3395(1978)64%3A2%3C365%3ASMPORD%3E2.0.CO%3B2-I.

Olsen, J., M. Perry. 1997. Watershield Use by Ring-Necked Ducks. Northeastern Naturalist, 4(3): 197-204. Accessed March 20, 2010 at http://www.jstor.org.proxy.lib.umich.edu/sici?origin=sfx%3Asfx&sici=1092-6194(1997)4%3A3%3C197%3AWUBRD%3E2.0.CO%3B2-R.

Torrence, S., M. Butler. 2006. Spatial structure of a diving duck (Aythya, Oxyura) guild: hwo does habitat structure and competition influence diving duck habitat use within northern prairie wetlands. Canadian Journal of Zoology, 84(9): 1358-1367. Accessed April 13, 2010 at http://proquest.umi.com/pqdlink?vinst=PROD&fmt=6&startpage=-1&ver=1&clientid=17822&vname=PQD&RQT=309&did=1189227701&exp=04-14-2015&scaling=FULL&vtype=PQD&rqt=309&TS=1271370083&clientId=17822.