Animal Diversity Web

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)

• Biogeographic Regions
• nearctic
  • native
• neotropical
  • native

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)

• Habitat Regions
• temperate
• tropical
• terrestrial
• freshwater

• Terrestrial Biomes
• savanna or grassland

• Aquatic Biomes
• lakes and ponds
• rivers and streams
• coastal
• brackish water

• Wetlands
• marsh
• bog

• Other Habitat Features
• agricultural
• riparian
• estuarine

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)

• Other Physical Features
• endothermic
• homoiothermic
• bilateral symmetry

• 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)

• Mating System
• monogamous

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)

• Key Reproductive Features
• iteroparous
• seasonal breeding
• gonochoric/gonochoristic/dioecious (sexes separate)
• sexual
• fertilization
• oviparous

• 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)

• Range lifespan
  Status: wild

  20.3 (high) years

• Average lifespan
  Status: wild

  245 months

  Bird Banding Laboratory

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)

• Key Behaviors
• flies
• natatorial
• diurnal
• motile
• migratory
• solitary
• social

• 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)

• Communication Channels
• visual
• acoustic

• Other Communication Modes
• duets

• Perception Channels
• visual
• tactile
• acoustic
• chemical

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)

• Primary Diet
• herbivore
  • folivore

• 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)

• Known Predators

  • Red fox (Vulpes vulpes)
  • Raccoons (Procyon lotor)
  • Northern harriers (Circus cyaneus)
  • Great horned owls (Bubo virginianus)
  • American mink (Neovison vison)
  • Bald eagles (Haliaeetus leucocephalus)
  • Peregrine falcons (Falco peregrinus)
  • Common snapping turtles (Chelydra serpentina)
  • Muskrats (Ondatra zibethicus)
  • Skunk (Mephitis mephitis)
  • Domestic dogs (Canis familiaris)
  • Pike (Esox lucius)
  • Bass (Micropterus)
  • Crows (Corvus brachyrhynchos)
  • Ravens (Corvus corax)

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)

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)

• IUCN Red List

  Least Concern
  More information

• IUCN Red List

  Least Concern
  More information

• US Migratory Bird Act

  Protected

• US Federal List

  No special status

• CITES

  No special status

• State of Michigan List

  No special status

Con­trib­u­tors

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

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.