Illinois Natural History Survey - University of Illinois

Gadwall
Anas strepera

 

Taxonomy
Occurence in Illinois
Status
Habitat associations
Guilds
Food-habits
Environmental associations
Life history
Management practices
References


TAXONOMY

 

  • Phylum: Chordata
  • Class: Aves
  • Order: Anseriformes
  • Family: Anatidae
  • Genus: Anas
  • Species: Anas strepera
  • Authority: Linnaeus

Comments on taxonomy:
Other names: "aka gray duck, gray wigeon, creek duck, bleating duck, speckle-belly, blarting duck, red wing *04*; gray mallard *05*."

 


OCCURENCE IN ILLINOIS

Fairly common migrant; fairly common winter resident in south; uncommon winter resident in central and north; rare summer (nonbreeding) resident in north and central.

 


STATUS

Items in bold indicate applicable categories
Forest Service Categories: S = recommended for regional sensitive status, F = forest listed species, M = management indicator species

Federal Status:

Endangered Threatened Proposed for listing
Candidate for proposal Recovery plan approved Recovery plan received (USFWS)
Recovery plan in preparation Under notice of review Delisted
Migratory EPA indicator Forest Serv.- Shawnee species

State Status:

Endangered Threatened Proposed

Other:

Game Furbearer Nongame protected
Sportfish Commercial Pest None of the above

Comments on status:
The gadwall is protected by the Illinois wildlife code of 1971 *06* and the Migratory Bird Treaty Act of 1918 *07*.

 


HABITAT ASSOCIATIONS

Items in bold indicate applicable categories

General habitat:

Unknown Terrestrial Aquatic Riparian

USFS timber inventory forest size class:

Unknown Unstocked Seedling Sapling
Seedling/sapling Pole Mature Over mature

Land use and land cover:

Unknown   Urban Residential
Commercial
Industrial
Transportation, communication
Complex industrial/commercial
Mixed
Other
Agricultural Crop, pasture
Orchards, groves, nurseries
Feedlot
Other
Rangeland Herbaceous
Shrub and brush
Mixed
Forestland Deciduous
Evergreen
Mixed
Water Stream
Lake
Reservoir
Bay
Wetland Forest
Non-forest
Barren Salt flat
Beach
Sand
Rock
Mine
Transit
Mix

 


Forest cover types: No records.

Associated tree species: No records.

 

National wetland inventory classifications:

SystemSubsystemClassSubclassWater regime modifiersWater chemistry
Lacustrine Littoral Aquatic bed
Emergent vegetation
Flat
Open water of unknown bottom type
  Unknown/umspecified Unknown/umspecified
Palustrine   Aquatic bed
Emergent vegetation
Flat
Open water of unknown bottom type
  Unknown/umspecified Unknown/umspecified
Riverine Lower perennial Aquatic bed
Emergent vegetation
Flat
Open water of unknown bottom type
  Unknown/umspecified Unknown/umspecified

High value habitats

HabitatStructural stageSeason
Cropland and pasture
Herbaceous rangeland
Evergreen forestland
Streams and canals
Lakes
Reservoirs
Bays and estuaries
Nonforested wetland
Not applicable (HVAL-HAB cover) All

Species-habitat interrelations: Breeds near lakes, ponds, marshes *00*; freshwater, shores of lakes and rivers, concealed by reeds, grasses, bushes that grow near shore or overhang it *04*; saltmarsh meadows, saltmeadow cordgrass, and saltgrass 1 foot high or less *09*; intermountain marshes, tallgrass prairie in areas outside principle breeding ground, mixed prairie, parklands, shortgrass, deltas, boreal forest of Canada, coast of Alaska, freshwater impoundments created on brackish marshes of national wildlife refuges and state wildlife management areas of east coast *05*; freshwater lakes and pools with plenty of cover, marshes, and streams; not numerous in saltwater, more numerous inland than on coasts *10*; grasslands, alkaline sloughs, grassy islands, alkaline marshes prefered over those with low salt concentratoins, more numerous on marshes, or deep and open water marshes *13*; generally wooded and thick brushed aras avoided, prefers islands surrounded by open water, open areas with emergent vegetation *11*.

 


GUILDS

Feed-guilding:

HabitatStructural stageSeasonFeed-guilds
Water Not applicable (HVAL-HAB cover) All Terrestrial surface-flowers and fruits of grass/grasslike vegetation
Terrestrial surface-leaves flowers, fruits, seeds of deciduous shrubs
Terrestrial surface-leaves, twigs, flowers, fruits, seeds of deciduous trees
Water bottom-aquatic bed, filamentous algae
Water column-filamentous algae
Water surface-filamentous algae
Water bottom-aquatic bed, rooted vascular plants
Water column-rooted vascular plants
Water surface-floating vascular plants
Water surface-rooted herbaceous plants at surface
Water surface-rooted herbaceous plants through surface
Water bottom-aquatic bed, arthropods
Water bottom-aquatic bed, invertebrates other than zooplankton or arthropods
Water column- arthropods
Water column- invertebrates other than zooplankton or arthropods
Water surface- arthropods
Water surface- invertebrates other than zooplankton or arthropods
Water bottom-aquatic bed, amphibians
Water column- amphibians
Water surface- amphibians

Comments on feed-guilding:
Good diver, usually in pairs or small bunches with other ducks *04*; feed in open water more often than other dabblers *11*; feed in shallow marshes and ponds, may feed rarely on grass pastures or upland grain fields *03*; will dive for food, usually dabbles *08*; almost exclusively surface-feeders, tip-up to feed in shallow marshes with abundant submerged plant life growing close to surface *13*.

Breed-guilding:

HabitatStructural stageSeasonBreed-Guilds
Cropland and pasture
Herbaceous rangeland
Evergreen forestland
Streams and canals
Lakes
Reservoirs
Bays and estuaries
Nonforested wetland
Not applicable (HVAL-HAB cover) Spring/summer Terrestrial surface Terrestrial surface, marshy areas with hydrophytes but not hydric soils
Terrestrial surface, grass and grasslike vegetation
Terrestrial surface, forb vegetation
Surface of water column-river/lake/marsh, unconsolidated rooted herbaceous plants
River/lake/marsh, vascular plants- emergent, nonwoody

 


FOOD-HABITS

Trophic level is OMNIVORE

Food itemLife stage/plant part
Plants Roots, bole/stem, leaves/needles, fruit/seeds
Chlorophyta (green algae) Not applicable
Rhodophyta (red algae) Not applicable
Tracehophyta (vascular plants) Roots, bole/stem, leaves/needles, fruit/seeds
Spermopsida (seed plants) Roots, bole/stem, leaves/needles, fruit/seeds
Angiospermae (flowering plants) Roots, bole/stem, leaves/needles, fruit/seeds
Fagaceae (beech, oak) Fruit/seeds
Polygonaceae (buckwheat, rhubarb) Fruit/seeds
Monocotyledonae (monocots) Roots, bole/stem, leaves/needles, fruit/seeds
Hydrocharitaceae (tape grass, water weed) Roots, leaves
Poaceae (grass) Roots, bole/stem, leaves/needles, fruit/seeds
Poaceae (grass): Oats, wheat, barley Fruit/seeds
Mollusca Adult
Insecta Larva, adult
Hemiptera Adult
Coleoptera (beetles) Adult
Diptera (flies, midges, mosquitoes) Adult
Osteichthyes (bony fishes) Juvenile, adult
Amphibians Adult
Important:
Plants Roots, bole/stem, leaves/needles, fruit/seeds
Juvenile:
Plants Leaves/needles
Adult:
Plants Roots, bole/stem, leaves/needles, fruit/seeds
Chlorophyta (green algae) Not applicable
Rhodophyta (red algae) Not applicable
Tracehophyta (vascular plants) Roots, bole/stem, leaves/needles, fruit/seeds
Spermopsida (seed plants) Roots, bole/stem, leaves/needles, fruit/seeds
Angiospermae (flowering plants) Roots, bole/stem, leaves/needles, fruit/seeds
Fagaceae (beech, oak) Fruit/seeds
Polygonaceae (buckwheat, rhubarb) Fruit/seeds
Monocotyledonae (monocots) Roots, bole/stem, leaves/needles, fruit/seeds
Hydrocharitaceae (tape grass, water weed) Roots, leaves
Poaceae (grass) Roots, bole/stem, leaves/needles, fruit/seeds
Poaceae (grass): Oats, wheat, barley Fruit/seeds
Mollusca Adult
Insecta Larva, adult
Hemiptera Adult
Coleoptera (beetles) Adult
Diptera (flies, midges, mosquitoes) Adult
Osteichthyes (bony fishes) Juvenile, adult
Amphibians Adult

Comments on food habits: 
General: Feed mainly on leaves and stems rather than seeds of grasses, sedges, pondweeds and other aquatic plants; *05,11*. Vegetation 98% of diet, animal foods increase to 11% during the summer *08*. Foods include tender shoots of grasses, blades and roots of aquatic plants, seeds, nuts, acorns, insects, mollusks, small fish *04*; wigeon grass, submerged aquatics, pondweed, eelgrass, rootstalks of rice, cut-grass *09*; naiads, coontail, muskgrass, filamentous algae, prefer stems and leaves to seeds, cultivated oats, saltgrass, bulrush seeds, spike rush, seeds of millet, smartweed, buttonbush, green algae, vegetative parts of naiad *03*; wheat, barley, buckwheat, corn, sedges, arrowheads, water bugs, beetles, flies, insect larvae *08*; amphibians, aquatic insects *10*; wigeon grass, eelgrass, muskgrass, pondweed; freshwater; naiads, pondweek, red algae *05*.
Juvenile: Young feed themselves; stomach contents 67.54% animal and 32.46% vegetable matter *11*.
Adult: See [FH].


ENVIRONMENTAL ASSOCIATIONS

General:

  • pH: see comments
  • Flow: greater than 5000 cfs
  • Trophogenic zones: well-lighted upper layer of standing water (epilimnion)
  • Aquatic habitat: shallows with emergent vegetation (littoral zone)
  • Aquatic habitat zone: pelagic- needs open water
  • Water level: permanent
  • Water level: semipermanently flooded
  • Water level: seasonally flooded
  • Aquatic habitats: freshwater marsh
  • Aquatic habitats: swamp, general
  • Aquatic habitats: cypress swamp
  • Aquatic habitats: vegetated offshore islands
  • Aquatic habitats: pool areas
  • Aquatic habitats: lake weedbeds
  • Ecotones: old field/water
  • Ecotones: crop field/grassland
  • Ecotones: grassland/water
  • Pastures: unknown
  • Grassland: unknown
  • Meadows: unknown
  • Herbs-leguminous forbs: unknown
  • Coniferous forest: unknown
  • Hardwood forest: see comments
  • Ground cover- herbaceous canopy ave. ht: see comments
  • Human associations: wildlife refuges/sanctuaries
  • Unknown

Egg

  • Unknown

Comments on environmental associations:
General: Prefers alkaline waters *13*; saltgrass less than or equal to 1 foot tall *09*; cover 13-15 inches high *13*.
Resting adult: Wading site of males usually on bare shoreline or log or rock, often spend both day and night in water *11*; loaf on open water rather than shoreline sites.


LIFE HISTORY

Origin: Native *01*.

Physical description: Adult male breeding plumage, head and neck pale buff, spotted and streaked with brown, with crown darker; mantle and flanks finely vermiculated creamy buff and dark gray; wing mostly gray with white speculum sometimes concealed by long pointed scapulars; greater coverts black; median coverts chestnut; breast has dark crescentric markings but some birds appear more blotched or spotted; abdomen and vent white; upper and under tail coverts black; tail grayish-brown with paler outer feathers; bill slate gray and narrow; legs and feet orange-yellow *10*; adult female browner with coarser markings; under tail coverts speckled gray and brown; very little or no chestnut in wing; bill slate gray with dull orange border *10*; immature female very similar to adult *14*; male in eclipse and immature male similar to female *10*; downy young dark above, creamy white below, with a dark stripe through the eye *10*; folded wing male 260-282 mm, female 235-260 mm; culmen male=38-45 mm, female 36-42 mm; weight male 989 g, female 848 g *13*; length 480-580 mm *02*.

Reproduction: Breeding season May to late July in Chesapeake Bay *09*; may continue breeding until September *03*; incubation period 24-27 days *05*; brood size 6.87 young average *03*; will renest if first nest destroyed; continue to lay if incomplete clutches destroyed; ability to renest decreases as stage of incubation lengthens; move nest site when renesting; clutch size smaller for renests; hatching success same as for initial nests *03*; breed as yearlings unless hatched very late the previous summer *03*; pair bond formed in mid-fall by adult birds and in mid-winter by immatures *05*; renew bonds each year *13*; arrive on nesting area already paired *12*; most bonds dissolve by second week of nesting *05*; mating flight by 2 males and 1 female *08*; aerial chases increase progressively toward spring with a peak just prior to onset of incubation *13*; social display early in fall, except for juvenile birds, before in nuptial plumage, also a spring peak while in full plumage when strong bonds are established, male displays include grunt-whistle, head up-tail down, down-up, uttering burp whistle, males also 'burp' during aerial chases *18*; clutch size 8-12, creamy or buffy white *04*; average clutch 10.04 *05*; dump nest up to 20 eggs, egg size 40 x 55 mm *05*.

Behavior: Territoriality is not expressed on islands *13*; established males try to discourage new pairs from breeding in the same area but are often unsuccessful *13*; little intraspecific agression *12*; home range, flocks separate into pairs and select a loafing and feeding site, range 100 yards-3 miles in search for appropriate area, range 34-87 acres and includes loafing, feeding, and nest sites; may overlap, pairs seldom encounter each other; mobile ranges revolve around female; can successfully nest in crowded conditions *05*; share common areas for foraging or loafing but not simultaneously, establish home range 17 days after arriving on breeding grounds, during this period, paired birds remain gregarious and forage and loaf together *13*; migration, early establishment of bisexual flocks in fall, fall migration shows no sexual segregation *13*; swift flight *04*; fall September 1 - December 10, peak October 15 - November 20; spring March 10 - April 30, peak March 15 - April 15 *09*; 75% of North American population stages and winters in Louisiana, follows mid-plains migration corridor to a large extent, migrates at night in small to moderate sized flocks, only migrates during day when blizzards drive it from the greart plains *05*. Nest slightly hollow in a bunch of grass or reeds, usually near water, constructed of dry grass, lined with down and feathers *04*; nest in white top, juncus, buckbrush, nettle, greasewood, alfalfa, summer fallow fields, upland grasses, willows, tall dense vegetation, prefer unmowed vegetation and ungrazed land *05*; favor small islands, dikes in marshes, fields, meadows; less inclined than most ducks to nest over water in marshes, most on upland areas within 100 yards of water *05*; nest scooped out hollow under bushes or in thick grass *08*; cover dense, coarse vegetation on islands surrounded by open water, heavy brush, willows, 13-36 inches high, 90% concealed on all 4 sides, 70% from above as well, 85% 3-50 high, 90% concealed on all 4 sides, 70% from above as well, 85% 3-50 yards from water *13*; one of last to arrive on breeding areas, pairs search for nest site, fly low over meadow and upland areas, land in short vegetation, hen followed by drake, choose areas with high clumps of vegetation, nest material, suitable soil for scrapes *05*; after establishing home range, 11 days pass before nesting begins *13*; males may accompany female and brood for some time *05*; female leads young to feeding grounds, some distance from the nest site, travel to deepwater marshes and margins of impoundments, hens with broods adopt orphaned or deserted young, late broods more likely to be deserted while not fledged, young need good brood cover along edges of water to survive predators (especially gulls) *05*; young hide in weedbeds and can escape by diving *04*; may feign injury when surprised on the nest if incubation is far along. If harassed will often desert eggs and nest *00*; females travel with young up to 1 mile, no brood mergers *13*; 6 weeks after hatching, females molt and become flightless *12*; fledging period 48-52 days *05*; non-breeding habitat and behavior: winters to Mexico *00*; 20-40 degrees north latitude, most winter in Louisiana, Tennessee, South Carolina, Georgia, Florida, Arkansas, Alabama, Texas, and Mexico, a few on west coast *05*; brackish marshes and inlets *09*; inland ponds, marshy lakes, sloughs, swamps, brackish pools and estuaries along Louisiana and Texas coast *15*; males leave females on breeding grounds and gather to molt in flocks in marshy areas *05*.

Limiting factors: Predators: striped skunk, coyote, fox, badger, ground squirrel, racoon, crow, magpie, raven, california and ring- billed gulls; mammals more important predators *05*. "Diseases and parasites general reference *17,18*; bacterial: botulism *19*; chlamydiosis *20*; cholera *21,22*; viral: duck plague *23,24*; newcastle *25*; helminths: digenea *26*; nematodes *27*; trematodes *28*; protozoan: coocidia *29,30,31*; sarcocystis *32*; ectoparasites *33*; nutritional *15*; miscellaneous *16*."

Population parameters: Upward trend, numbers have almost doubled since the 1950's, long term cycles of abundance and scarcity *05*; average breeding population (1979) North America 1,607,000 *09*; mortality: immatures (year 1) 67% *05*; juvenile preflight 23% (most loss occur in first 18 days of life) *13*; annual adult mortality 52% *05*; overall mortality 60% annually *05*; hunting mortality Canada 77000, Alaska 800, United States 483600, total kill 561400 *13*; age ratio 1.6 immatures/adult bagged; corrected to 1.1 immatures/adult *05*; sex ratio adult 2.21 males/female bagged (68.8%); immature 1.1 males/females bagged (52.4%); overall 53-60% male *05*.

 


MANAGEMENT PRACTICES

Beneficial:

  • Maintaining natural areas and nature preserves
  • Maintaining unique or special habitat features (wetlands, snags, caves, cliffs, talises, etc.)
  • Controlling pollution
  • Practices other than those included on the ifwis list (see comments)
  • Creating impoundments
  • Developing/maintaining lakes and ponds
  • Developing/maintaining wetlands
  • Developing/maintaining mudflats
  • Protecting existing wetlands
  • Controlled grazing of domestic livestock
  • Regulating harvest of animal being described
  • Regulating hunting
  • Restricting human disturbance during migration, breeding, and nesting
  • Maintaining undisturbed resting areas for migrating birds

Adverse:

  • Practices other than those included on the IFWIS list (see comments)
  • Controlling water levels
  • Draining ponds/lakes
  • Draining wetlands
  • Clean farming
  • Applying pesticide on agricultural land
  • Applying herbicide
  • Applying insecticide

Existing:

  • Regulating harvest of animal being described
  • Regulating hunting

Comments on management practices:
Intensive agriculture and heavy grazing reduce relative numbers; land-use practices such as haying and summer fallow are destructive during nesting *11*; intensive recreational development *11*; maintain undisturbed resting areas for migrating birds; addition of resting ponds *11*.

 


REFERENCES

0. FOSTER, C. AND L. GRIBKO. 101 CHEATHAM HALL, BLACKSBURG, VA.

1. BOHLEN, H.D. 1975. AN ANNOTATED CHECK-LIST OF THE BIRDS OF ILLINOIS. ILLINOIS STATE MUSEUM POP. SCI. SERIES VOL. IX. 156 PP.

2. PETERSON, R.T. 1980. A FIELD GUIDE TO THE BIRDS. 4TH ED. HOUGHTON- MIFFLIN CO. BOSTON, MASS.

3. AMERICAN ORNITHOLOGISTS' UNION. 1983. CHECK-LIST OF NORTH AMERICAN BIRDS. 6TH ED. ALLEN PRESS INC. LAWRENCE, KN. 877 PP.

4. "UNKNOWN." 1936. BIRDS OF AMERICA. PEARSON, O.T., ED. GARDEN CITY PUBL. CO., GARDEN CITY, NY.

5. BELROSE, F.C. 1978. DUCKS, GEESE, AND SWANS OF NORTH AMERICA. 2ND ED. STACKPOLE BOOKS, HARRISBURG, PA.

6. ILLINOIS DEPT. CONSERVATION. 1980. CONSERVATION LAWS. CH. 61. WILDLIFE ART. II. PAR. 2.2. REPRINTED FROM ILLINOIS REVISED STATUTES 1979. WEST PUBL. CO., ST. PAUL, MN. 120 PP.

7. U.S. FISH & WILDLIFE SERVICE. 1983. CODE OF FEDERAL REGULATIONS. TITLE 50. WILDLIFE & FISHERIES CHAPTER 1 PP. 11-18 50 CFR 10.13. LIST OF MIGRATORY BIRDS. SPECIAL PUBL. FED. REGISTER GENERAL SERVICES ADMIN. OCT. 1.

8. KORTRIGHT, F.H. 1967. THE DUCKS, GEESE AND SWANS OF NORTH AMERICA. STACKPOLE BOOKS, HARRISBURG, PA.

9. MEANLY, B. 1982. WATERFOWL OF THE CHESAPEAKE BAY COUNTRY. TIDEWATER PUBL., CENTREVILLE, MD.

10. SOOTHILL, E. & P. WHITEHEAD. 1978. WILDFOWL OF THE WORLD. BLANDFORD PRESS.

11. PALMER, R.S. 1976. HANDBOOK OF NORTH AMERICAN BIRDS. VOL. II. YALE UNIV. PRESS, NEW HAVEN, CONN.

12. JOHNSGARD, P.A. 1978. DUCKS, GEESE AND SWANS OF THE WORLD. UNIV. NEBRASKA PRESS, LINCOLN.

13. JOHNSGARD, P.A. 1975. WATERFOWL OF NORTH AMERICA. INDIANA UNIV. PRESS, BLOOMINGTON.

14. ILLINOIS DEPT. OF CONSERVATION. 1984. 1984 WATERFOWL HUNTING INFORMATION. ILLINOIS DEPT. CONSERV., SPRINGFIELD, IL. PAMPHLET.

15. DHILLON, A.S. AND R.W. WINTERFIELD. 1983. SELENIUM-VITAMIN E DEFICIENCY IN CAPTIVE WILD DUCKS. AVIAN DIS. 27(2):527-530.

16. MACNEIL, A.C. & T. BARNARD. 1978. NECROPSY RESULTS IN FREE-FLYING AND CAPTIVE ANATIDAE IN BRITISH COLUMBIA. CAN. VET. J. 19:17-21.

17. HUMPHREYS, P. 1978. DUCKS, GEESE AND SWANS (ANSERIFORMES) PAGES 183- 209. ZOO AND WILD ANIMAL MED. FOWLER, M.E., ED. W.B. SAUNDERS CO., PA.

18. WOBESLER, G.A. 1981. DISEASES OF WILD WATERFOWL.

19. ROSEN, M.N. 1971. BOTULISM. PP. 100-117. INFECTIONS AND PARASITIC DISEASES OF WILD BIRDS. IOWA STATE UNIV., AMES, IA.

20. BURKHART, R.L. & L.A. PAGE. 1971. CHLAMYDIOSIS (ORNITHOSIS- PSITTACASIS) PP. 118-140. INFECTIONS & PARASITIC DISEASES OF WILD BIRDS. IOWA STATE UNIV., AMES, IA.

21. ODDO, A.F., ET AL. 1978. THE JANUARY 1977 AVIAN CHOLERA EPORNITIC IN N.W. CALIF. J. WILDL. DIS. 14:317-321.

22. ROSEN, M.N. 1971. AVIAN CHOLERA. PP. 39-74. INFECTIOUS AND PARASITIC DISEASES OF WILD BIRDS. IOWA STATE UNIV., AMES, IOWA.

23. BURGESS, E.C., ET AL. 1979. DUCK PLAGUE: A CARRIER STATE IN WATER FOWL. AVIAN DIS. 23(4):940-949.

24. SPIEKER, J.O. 1978. VIRULENCE ASSAY AND OTHER STUDIES OF SIX NORTH AMERICAN STRAINS OF DUCK PLAGUE VIRUS TESTED IN WILD AND DOMESTIC WATER FOWL. PH.D. DISS. UNIV. WIS. (MADISON) DISS. ABSTR. INT. B. SCI. ENG.

25. VICKERS, M.L. & R.P. HANSON. 1982. CHARACTERIZATION OF ISOLATES OF NEWCASTLE DISEASE VIRUS FROM MIGRATORY BIRDS AND TURKEYS. AVIAN DIS. 26(1):127-133.

26. SCOTT, M.E., ET AL. 1980. PREVALENCE AND INTENSITY OF TYPHLOCOELUM CUCUMERIUM (DIGENEA) IN WILD ANATIDS OF QUEBEC, CANADA. WILDL. DIS. 16(1):71-75.

27. WEHR, E.E. 1971. NEMATODES. PP. 185-233. INFECTIOUS AND PARASITIC DISEASES OF WILD BIRDS. IOWA STATE UNIV. AMES, IOWA.

28. VANDEVASSE, F.J. 1980. A REVIEW OF THE GENUS DENDRITO BILHARZIA SKRIJABIN AND ZAKHAROW. 1920. (TREMATODA - SCHISTOSOMATIDAE) PARASITOL. 66(5):814-822.

29. BRISTOL, J.R., ET AL. 1981. COCCIDICE OF SURFACE-FEEDING DUCKS FROM THE CENTRAL FLYWAY. TEXAS J. PARASITOL 67(2):276-277.

30. NATION, P.N. AND G. WOBESER. 1977. RENAL COCCIDIASIS IN WILD DUCKS IN SASKATCHEWAN. J. WILDL. DIS. 14:124-131.

31. TODD, K.S., JR. AND D.M. HAMMOND. 1971. CACCIDIA OF ANSERFORMES GALLIFORMES & PASSERFIORMES. PP. 234-287. INFECTION AND PARASITIC DISEASES OF WILD BIRDS. IOWA STATE UNIV. AMES, IOWA.

32. WOBESER, G. & R.J. CAWTHORN. 1982. GANULOMATOUS MYOSITIS IN ASSOCIATION WITH SARCOCYSTIS SP. INFECTION IN WILD DUCKS. AVIAN DIS. 26(2):412-418.

33. PETERS, H.S. 1936. A LIST OF EXTERNAL PARASITES FROM BIRDS OF THE EASTERN PART OF THE U.S. BIRD BANDING 7:9-27.

 


 

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