Description
Synonymy - Several subspecies, which lack the strong sexual dimorphism of A. p. platyrhynchos, not found in our area, were formerly recognized as full species: A. p. fulvigula, the Florida Duck; A. p. maculosa, the Mottled Duck; A. p. diazi, the Mexican Duck; A. p. wyvilliana, the Hawaiian Duck; A. p. laysanensis, the Laysan Teal (Johnsgard 1978). The American Black Duck, A. rubripes might also be regarded as a sexual monomorphic form of A. platyrhynchos (Ankney et al. 1986). Domestic ducks are descended from A. p. platyrhynchos.
Potentially Misidentified Species - The American Black Duck, Anas rubripes, has a very high degree of genetic similarity with the Mallard, with which it shares identical courtship displays. The two forms regularly hybridize (Ankney et al. 1986; Heusmann 1974; Heusmann 1991; Seymour 1990). Ankney et al. argue, on the basis of genetic data, that A. rubripes should be considered only a melanistic morph of the Mallard, Anas platyrhynchos, and does not deserve even subspecific status. Females of other dabbling ducks (Gadwall - A. strepera; Pintail- A. acuta, and others) can be confused with female mallards (Peterson 1980).
Taxonomy
| Kingdom | Phylum | Class | Order | Family | Genus |
|---|---|---|---|---|---|
| Animalia | Chordata | Aves | Anseriformes | Anatidae | Anas |
Synonyms
Invasion History
Chesapeake Bay Status
| First Record | Population | Range | Introduction | Residency | Source Region | Native Region | Vectors |
|---|---|---|---|---|---|---|---|
| 1913 | Established | Expanding | Introduced | Regular Resident | North America | Holarctic | Fisheries(Fisheries Intentional); Natural Dispersal(Natural Dispersal) |
History of Spread
Anas platyrhynchos(Mallard Duck) is native to Europe, Asia, and most of North America. This duck is also the wild ancestor of most domesticated duck breeds (Johnsgard 1978). Its status on the Atlantic coast of North America is somewhat obscure. Colonial writings suggest that Mallards were common along the coast from Maine to Florida in the 17th century, but had become only a rare visitor in New England by the 1830's. [Note that interpretation of the earliest records hinges on whether (Anas rubripes) and A. platyrhynchos were distinguished by explorers and colonists) (Heusmann 1991).]
The existence of A. rubripes as a morphologically distinct (although genetically) similar population, in spite of the absence of behavioral isolating mechanisms, argues for geographical isolation of the two 'species' before European colonization. A. platyrhynchos are considered to be adapted for grassland breeding, and A. rubripes, for breeding in forested wetlands (Heusmann 1974; Ankney et al. 1986). A. platyrhynchos were apparently present as wintering birds, but probably absent as breeders on the Atlantic coast at the beginning of European colonization (Johnsgard 1967; Heusmann 1974; Heussmann 1991).
In NY, GA, and FL, A. platyrhynchos were still common in the middle 1800's (Heusmann 1991), but by 1900 they were rare in NY (Heusmann 1991) and were not mentioned as a breeding bird in a book on the birds of MD (Kirkwood 1895). However, A. platyrhynchos remained abundant as a wintering bird from VA southwards (Bailey 1913; Heusmann 1991). In the 20th century, the Mallard's breeding range was extended eastward, and now, abundant breeding populations occur on the Atlantic Coast (Johnsgard 1967; Johnsgard and DiSilvestro 1976; Heusmann 1991) and through most of North America (Sauer et al. 1996). A. platyrhynchos are included in this database because: (1) Intentional release of farm-raised birds by state fish and game departments and private individuals appears to be a major factor in colonization (or recolonization) of the Atlantic coast. 1.8 million birds have been released in the Atlantic Flyway since 1940. (2) Populations of A. platyrhynchos in urban and suburban areas often consist of mixtures of birds of wild and domestic origin and their hybrids (Figley and VanDruff 1982).
A. platyrhynchos populations in the Atlantic Flyway are believed to have declined by 50-80% from 1880 to 1910 due to extensive market hunting. This depletion prompted extensive duck releases, as described above. In 1906, the eastern limit of breeding for A. platyrhynchos was eastern Ontario and locally in western NY, south to western MD. Johnsgard (1967) and Johnsgard and DiSilvestro 1976) have described trends in relative abundance of A. platyrhynchos and A. rubripes in Christmas Bird count data, giving A.platyrhynchos abundance as a percentage of the total of the two species. From MD north to MA, in 1900-1939, A. platyrhynchos comprised 6% to 7% of combined wintering A. platyrhynchos and A. rubripes in Christmas bird counts. In VA to FL, A. platyrhynchos at this time were 10-35% of the combined population. By 1970-74, in MD to MA, Mallards were 63 to 17% of the combined population, and 53-81% in VA to FL (Johnsgard 1967; Johnsgard and DiSilvestro 1976). The breeding range of A. platyrhynchos is also extending northeastward into the Maritime provinces of Canada (D'Eon et al. 1995). Increasing co-occurrence of A. rubripes and A. platyrhynchos has led to frequent hybridization, threatening the existence of the A. rubripes as a distinct population (Johnsgard 1967; Johnsgard and DiSilvestro 1976; Heusmann 1991).
A. platyrhynchos were mentioned as a common winter resident, and as a migrant, but not as breeding birds in MD by Kirkwood (1895), and by Cooke (1908), for the Washington DC area. In VA in 1913, they were observed breeding 'sparingly in the wild state in numerous creeks emptying into the upper James River. Would not be surprised if it did not also breed in the upper end of Back Bay, though as yet I have no evidence of their doing so' (Bailey 1913). Early releases and breeding of Mallards may have resulted from the widespread practice of purchasing and using 'live decoy' birds to attract wild flocks. These birds often later escaped or were released, especially after the practice became illegal in 1935. By 1958, in MD 'scattered pairs of nesting birds that give every appearance of being feral have been noted in tidewater areas and on inland ponds, lakes, and streams in all sections. Whether any of these are derived from the introduced stock are problematical' (Stewart and Robbins 1958). 'Maryland is the only state in the flyway that continues to release Mallards as part of a state program. Between 1974 and 1988, the state released over 300,000 mallards (L. J. Hindman; pers; communication). F. Rohwer reported that during 1988 and 1989, private sources in Maryland released an additional 240,000 birds (Atl. Waterfowl Council meeting, 28 July 1990).' A. platyrhynchos are now widespread breeders in MD, DE, and coastal VA (Heusmann 1991).
History References - Ankney et al. 1986; Bailey 1913; Cooke 1908; Cooke 1921; D'Eon et al. 1995; Figley and VanDruff 1982; Heusmann 1974; Heusmann 1991; Johnsgard 1967; Johnsgard 1978; Johnsgard and DiSilvestro 1976; Kirkwood 1895; Sauer et al. 1996; Stewart and Robbins 1958; Wass 1972
Invasion Comments
Probable Vectors, Invasion Status - Anas platyrhynchos does not easily fit into our categories of invasion status, because populations in the Chesapeake region have probably been derived from a number of sources and arrived through several vectors. It is not clear whether the appearance of breeding birds in the area counts as an introduction or a re-introduction of the species. Natural dispersal of western populations which bred in man-modified habitats, mass releases of birds bred in game farms, and hybridization of urban birds with domestic ducks have probably all contributed to growing Mallard populations in the Chesapeake and elsewhere on the Atlantic seaboard (Heussmann 1991).
Ecology
Environmental Tolerances
| For Survival | For Reproduction | |||
|---|---|---|---|---|
| Minimum | Maximum | Minimum | Maximum | |
| Temperature (ºC) | ||||
| Salinity (‰) | 35.0 | 0.0 | 0.0 | 5.0 |
| Oxygen | ||||
| pH | ||||
| Salinity Range | fresh-eu |
Age and Growth
| Male | Female | |
|---|---|---|
| Minimum Adult Size (mm) | 400.0 | 400.0 |
| Typical Adult Size (mm) | 530.0 | 530.0 |
| Maximum Adult Size (mm) | 660.0 | 660.0 |
| Maximum Longevity (yrs) | ||
| Typical Longevity (yrs | 3.0 | 3.0 |
Reproduction
| Start | Peak | End | |
|---|---|---|---|
| Reproductive Season | |||
| Typical Number of Young Per Reproductive Event |
|||
| Sexuality Mode(s) | |||
| Mode(s) of Asexual Reproduction |
|||
| Fertilization Type(s) | |||
| More than One Reproduction Event per Year |
|||
| Reproductive Startegy | |||
| Egg/Seed Form |
Impacts
Economic Impacts in Chesapeake Bay
Breeding, resident populations of Anas platyrhynchos (Mallard Ducks) have had a wide range of impacts in the Eastern United States, which appear to apply to the Chesapeake Bay region.
Fisheries - A. platyrhynchos are a favorite bird of hunters (Bailey 1913), and bore the brunt of market hunting the late 1800's, a fact which led to the extensive release of farm-raised birds on the East Coast after 1900 (Heusmann 1991). More than 1.8 million birds have been stocked in the Atlantic Flyway, including 300,000 released in MA between 1974 and 1988 (Heusmann 1991). A. platyrhynchos probably represent a considerable source of money generated by state agencies by hunting licenses and to businesses equipping duck-hunters. A. platyrhynchos are believed to be less wary than A. rubripes, and may also be preferred by hunters (Ankney et al. 1987). However, banding analyses indicate that harvest rates are similar (Rusch et al. 1989).
On the other hand, to the extent that the native A. rubripes is valued by hunters and lovers of wildlife, competitive displacement and hybridization with the A. platyrhynchos is seen as a possible negative impact. A. rubripes are still common in eastern North America, but have been declining at the rate of about 3%/year for the last 30 years (Rusch et al. 1989). The role of A. platyrhynchos as a cause of this decline, as opposed to over-hunting, habitat alteration, etc., is a matter of debate (Ankney et al. 1987; Conroy et al. 1989; Longcore et al. 1998; McCauley et al. 1998; Merendino et al. 1993). As of 1991, MD was the only state releasing A. platyrhynchos on an official basis (Heusmann 1991). On Chesapeake Bay islands, A.platyrhynchos and A. rubripes had similar nest success rates in undisturbed areas, but A. platyrhynchos were more tolerant of human disturbance than A. rubripes (Krementz et al. 1992), so that maintaining undisturbed nesting areas may be critical in maintaining A. rubripes populations.
Aesthetics - A. platyrhynchos have become a familiar form of urban and suburban wildlife on the Atlantic coast and many other parts of the world. A. platyrhynchos are frequently fed bread and other human foods by waterfront residents and park visitors. Ninety-five percent of residents of a coastal NJ community considered the ducks to be a positive asset, 5% complained about damage to yards and gardens (Figley and Van Druff 1982). Similarly, in a central WI city, Stevens Point, 64 of 100 people surveyed said they fed A. platyrhynchos in a city park, suggesting that in this park, 7,000 people might be feeding ducks at least once a month. Ducks were especially attractive to families with children (Barrett 1992).
Problems associated with dense A. platyrhynchos populations include defecation on grass, damage to plants, and degraded water quality due to feces and decomposing food (Barrett 1992; Figley and Van Druff 1982). Many parks and recreational areas now advise against feeding ducks for these reasons, as well as the ill effects of large quantities of low-nutrient food and disease risks to the birds from dense aggregations in feeding areas (Barrett 1992).
Habitat Change - Dense urban flocks can result in elevated nutrients, and low diversities of plankton, periphyton, and benthos, in the waters where they reside (Figley and Van Druff 1981).
Health - Dense duck populations can result in high coliform counts in adjacent waters (Figley and Van Druff 1981), which can result in closure of waters to fishing, swimming, and shellfishing.
References- Ankney et al. 1987; Bailey 1913; Barrett 1992; Conroy et al. 1989; Figley and Van Druff 1981; Heusmann 1991; Krementz et al. 1992; Longcore et al. 1998; McCauley et al. 1998; Merendino et al. 1993; Rusch et al. 1989
Economic Impacts Outside of Chesapeake Bay
Costs and benefits discussed under 'Economic impacts' apply to the entire East coast and to urban A. platyrhynchos populations throughout North America. Like the A. rubripes, local morphologically distinct A. platyrhynchos populations in FL ('Florida Duck' and the Gulf of Mexico 'Mottled Duck', and Mexico 'Mexican Duck', as well as the Laysan and Hawaiian Ducks are vulnerable to competition and hybridization with introduced common A. platyrhynchos (Johnsgard 1978).
References- Johnsgard 1978
Ecological Impacts on Chesapeake Native Species
Anas platyrhynchos (Mallard Ducks) chief ecological impact seems to be on the closely related, possibly conspecific, Anas rubripes (American Black Duck) from which it was probably geographically isolated before European colonization (Ankney et al. 1986). In much of eastern North America, A. rubripes appear to have declined as A. platyrhynchos have increased (Ankney et al. 1987; Johnsgard 1967; Johnsgard and DiSilvestro 1976; Rusch et al. 1989). While interactions among these two species have been well-studied, conclusions of different studies on the importance of competition and hybridization in the decline of A. rubripes are contradictory. This may reflect the difficulty in generalizing the behavior of two ecologically and behaviorally versatile species.
Competition - A. platyrhynchos and A. rubripes are very similar in morphology, feeding habits, and population dynamics. A. platyrhynchos tend to prefer grassy or bushy areas for breeding, and fresher water for wintering, but they use estuarine areas as well. A. rubripes prefer to breed in forested habitat including swamps, bogs, and wooded shorelines, but along Chesapeake Bay they use tidal marshes extensively. Overlap between the species during wintering and breeding is substantial along Chesapeake Bay. (Johnsgard 1978; Krementz et al. 1992; Stewart and Robbins 1958). A. platyrhynchos and A. rubripes diets along the James River in VA were very similar (Perry 1981). However, a comparison of reproductive success of the two ducks on Chesapeake islands found no consistent differences in nest success and clutch size, but in 2 of 4 years, A. platyrhynchos had higher rates of nest success in areas with the most human disturbance (Krementz et al. 1992). A study in northern ME also found no difference in brood size between A. platyrhynchos and A. rubripes, whether nesting in single species aggregations, or with the two species mixed (Longcore et al. 1998b). . Mallards are much more tolerant of people, and tend to predominate in urbanized areas, so that increasing human population along the Bay probably favors this species (Krementz et al. 1992; Morton 1998). Competition with other dabbling ducks nesting in the Chesapeake region [eg., A. strepera; (Gadwell). A. discors (Blue-winged Teal) is possible but not documented.
In southern Ontario, A. platyrhynchos invaded the most productive (based on chemical and physical indicators, e.g. pH, ions, nutrients, shoreline irregularity) wetlands first. Breeding A. rubripes now persist only on the least productive wetlands. This pattern is suggestive of competitive exclusion (Merendino et al. 1993). However, no evidence was found for competitive exclusion of A. rubripes by A. platyrhynchos in ME, as reflected either in brood size (Longcore et al. 1998), or in the outcome of aggressive interactions (McCauley et al. 1998). McCauley et al. (1998) found that where the two species were nesting sympatrically in ME, A. platyrhynchos and A. rubripes drakes initiated aggressive interactions with equal frequency. A. platyrhynchos 'won' 63% of the encounters they initiated with A.rubripes, while Black Ducks 'won' 89% of the intractions they initiated with A. platyrhynchos. They found few cases in which one species displaced a nesting pair of the other species form a wetland, and no evidence that A. rubripes were more likely to be excluded than A. platyrhynchos (McCauley et al. 1998). A behavioral study of Mallard and American Black Ducks in Chesapeake Bay found no evidence for consistent comptitive displacment of Black Ducks by Mallards (Morton 1998). The relative importance of competition, hybridization, habitat change, hunting pressures, and differential responses of A. platyrhynchos and A. rubripes to these factors need to be evaluated in order to develop effective policies for preserving A. rubripes populations (Ankney et al. 1989; Conroy et al. 1989; Longcore et al. 1998; McCauley et al. 1998; Rusch et al. 1989).
Hybridization - A. platyrhynchos and A. rubripes lack behavioral and genetic isolating mechanisms, and hybridize when ever they come into contact. Mean genetic distances between A. platyrhynchos and A. rubripes populations were virtually identical to distances between populations of the same species, indicating that very little genetic differentiation exists between the two forms (Ankney et al. 1986). Seventy three percent of a group of 33 unpaired A. rubripes females mated with A. platyrhynchos drakes, although A. platyrhynchos males preferred A. platyrhynchos females. A. platyrhynchos Drakes are believed to be more aggressive than male A. rubripes. Forced copulations by male A. platyrhynchos with A. rubripes and A. platyrhynchos females appeared to be frequent, while the same behavior is rare in A. rubripes drakes. Northern wintering A. platyrhynchos flocks often have an excess of males, which leads to their mating with A. rubripes females. The expansion of A. platyrhynchos populations may also promote hybridization (Brodsky and Weatherhead 1984). The incidence of hybridization in the eastern United States has been steadily increasing (Johnsgard 1967; Johnsgard and DiSilvestro 1976; Heussman 1988). Ankney et al. (1987) have argued that the hybridization (and/or competition) with A. platyrhynchos was the chief factor in the decline of A. platyrhynchos in Ontario, but this interpretation of their data has been disputed (Conroy et al. 1989; Longore et al. 1998; McCauley et al. 1998). A study of breeding of the two species in Chesapeake Bay found temporal differences in courting, few cases of interspecies pairing, and reduced breeding success of hybrids (Morton 1998). Morton (1998) suggests that the decline of the American Black Duck is largely due to its wariness and low tolerance for human disturbances.
Habitat Change - Especially in urban habitats, A. platyrhynchos populations fed by humans can affect water quality through defecation and decomposition of uneaten food, mostly bread. (Figley and Van Druff 1982).
References - Ankney et al. 1986; Ankney et al. 1987; Brodsky and Weatherhead 1984; Conroy et al. 1989; Figley and Van Druff 1982; Heusmann 1988; Johnsgard 1967; Johnsgard and DiSilvestro 1976; Krementz et al. 1992; Longcore et al. 1998; McCauley et al. 1998; Merendino et al. 1993; Rusch et al. 1989; Stewart and Robbins 1958
Ecological Impacts on Other Chesapeake Non-Native Species
Interactions of breeding, nonmigratory Anas platyrhynchos (Mallard Duck) with other nonidigenous waterfowl in the Chesapeake Bay region, such as Cygnus olor (Mute Swan) and resident Branta canadensis (Canada Geese) have not been studied, to our knowledge.
Herbivory - A. platyrhynchos are important herbivores on native and introduced plant species. Perry (1981) lists seeds of a number of introduced plants in the stomach contents of A. platyrhynchos from the tidal fresh James River, including Murdannia keisak, and trace quantities of Eclipta prostrata, Polygonum hydropiper, P. persicaria. Hydrilla verticillata appears to be extensively utilized by wintering A. platyrhynchos in reservoirs in the Potomac drainage (Hench et al. 1994), and in the tidal Potomac (Hurley 1990; Phelps 1994).
References - Hench et al. 1994; Hurley 1990; Perry 1981; Phelps 1994
References
Ankney, C. Davison; Dennis, Darrel G.; Wishard, Lisa N.; Seeb, James E. (1986) Low genic variation between black ducks and mallards, The Auk 103: 701-709Ankney, C. Davison; Dennis, Darrell G.; Bailey, Robert C. (1987) Increasing Mallards, decreasing American Black Ducks: Coincidence or cause and effect?, journal of Wildlife Management 51: 523-529
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Barnes, Gregory C.; Nudds, Thomas D. (1991) Salt tolerance in American Black Ducks, Mallards, and their F1-hybrids, The Auk 108: 89-98
Barrett, Gabrielle (1992) Public attitudes toward park mallards in Stevens Point, Wisconsin, Passenger Pigeon 54: 119-123
Brodsky, Lynn M.; Weatherhead, Patrick J. (1984) Behavioral and ecological factors contributing to American Black Duck-Mallard hybridization., Journal of Wildlife Management 48: 846-852
Conroy, Michael J.; Barnes, Gregory G.; Bethke, Raymond W.; Nudds, Thomas D. (1989) Increasing Mallards, decreasing American Black Ducks: no evidence for cause and effect: a comment., journal of Wildlife Management 53: 1065-1071
Cooke, May T. (1921) Birds of the Washington region, Proceedings of the Biological Society of Washington 34: 1-22
Cooke, Wells W. (1908) Bird migration in the District of Columbia, Proceedings of the Biological Society of Washington 21: 107-118
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Hench, John E.; Gibbs, Ron; Hench, Jayne S. (1994) Some observations on Hydrilla and wintering waterfowl in Montogomery County, Maryland, The Maryland Naturalist 38: 3-9
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Heusmann, H. W. (1988) Influence of wintering Mallards on hybridization in American Black Ducks, Journal of Field Ornithology 59: 258-261
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Krementz, David G.; Stotts, Daniel B.; Pendleton, Grey W.; Hines, J. E.; Stotts, Vernon D. (1992) Comparative productivity of American Black ducks and Mallards nesting on Chesapeake Bay Islands, Canadian Journal of Zoology 70: 225-228
Longcore, Jerry R.; Clugston, David A.; McAuley, Daniel G. (1998) Brood sizes of sympatric American Black Ducks and Mallards in Maine, journal of Wildlife Management 62: 142-151
McCauley, Daniel G.; Clugston, David A.; Longcore, Jerry R. (1998) Outcome of aggressive interactions between American Black ducks and Mallards during the breeding season, journal of Wildlife Management 62: 134-141
Merendino, M. Todd; Ankney, Davison; Dennis, Darrell G. (1993) Increasing Mallards, decreasing American Black Ducks: more evidence for cause and effect, Journal of Wildlife Management 57: 199-208
Perry, Matthew C. (1981) Asiatic Clam (Corbicula manilensis) and other foods used by waterfowl in the James River, Virginia, Estuaries 4: 229-233
Peterson, Roger T. (1980) A guide to the birds, , Boston. Pp.
Phelps, Harriette L. (1994) The Asiatic clam (Corbicula fluminea) invasion and system-level ecological change in the Potomac River estuary near Washington, D.C., Estuaries 17: 614-621
Robbins, Chandler S.; Blom, Eirik A. T. (1996) Atlas of the Breeding Birds of Maryland and the District of Columbia, , Pittsburgh. Pp. 70-305
Rusch, Donald H.; Ankney, C. Davison; Boyd, Hugh; Longcore, Jerry R.; Montalbano, Frank III; Ringelman, James K.; Stotts, Vernon D. (1989) Population ecology and harvest of the Amercan Black Duck: a review, Wildlife Ecology Bulletin 17: 379-406
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Seymour, N. R. (1990) Forced copulation in sympatric American Black Ducks and Mallards in Nova Scotia, Canadian Journal of Zoology 68: 1691-1696
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