Zoology

Mottled Duck



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The mottled duck (Anas fulvigula maculosa) is a large duck with a mottled fuscous-brown plumage (Bellrose 1980). The sexual dimorphism of the mottled duck is hard to distinguish because both sexes have nearly the same coloration the exception is that the female has lighter plumage than that of the male. One perceivable characteristic betwixt the female and male is the coloration of the upper mandible: the color in the male mandible varies between olive to yellow, whereas in females the coloration varies from orange to olive with erratic black or brown spots. Another difference between male and female mottled ducks is that the legs of males are bright orange and the females are dull orange in color (Moorman and Gray 1994).

The mottled duck is found in southern Florida and along the Gulf Coast of Louisiana and Texas and down to the Alvarado Lagoon near Veracruz (Bellrose 1980). Its primary habitat is coastal marshes and lagoons (Knopf 1995). The mottled duck is of the dabbling duck variety preferring the freshwater prairie ponds of Florida and the turbid marsh ponds along the Golf Cost (Corman and Gray 1994). The range of a single mottled duck is natal in that it rarely, if ever, travels farther than a couple hundred miles of its birth site (Bellrose 1980). The abundance of the mottled ducks are performed through an annual systematic population survey in Florida only, other parts of the ducks range are not gathered. This is problematic since mottled ducks range near their natal site, which includes the Gulf Coast of Louisiana and Texas as well as far south as Veracruz. In 1991 the spring and fall survey estimated around 28000 and 56000 birds respectively in Florida alone (Moorman and Gray 1994). Some concern about total abundance has arisen due to conflicting reports; in areas where mottled ducks are hunted bag limits are more restrictive (Elsey and Trosclair and Linscombe 2004).

It is unclear as to the evolutionary divergence of the mottled duck from that of the Mallard; however, mottled ducks and Mallards have been known to hybridize (Moorman and Gray 1994). The apparent reason for the hybridization is because the mottled ducks coloration is similar to a female mallard. The mottled duck mating rituals, which are similar to those of the mallard, lead one to believe that the infrequency of crossbreeding with the mallard can be summed up by its "pair formation; which begins as early as August, much earlier than other ducks;" (Moorman and Gray 1994). Another reason why crossbreeding is uncommon between mallards and mottled ducks is that mottled ducks are considered to be monogamous throughout the incubation of their eggs. It is unclear if the same ducks will continue monogamy through successive breeding seasons.

The clutch size ranges from eight to twelve eggs, which is incubated exclusively by the female; she will spend 83% of her time incubating the eggs. When the birds hatch they are precocial and leave the nesting site soon after. They hatch eyes open and fully covered with downy plumage. The parental care of the brood is left entirely to the female. She will move the brood from the nesting site to a rearing site where there is an abundant amount of vegetation. Brood rearing habitats typically consist of wetlands having a 1:1 ratio of open water and emergent vegetation. Broods usually disband at 65 to 70 days of age, ducklings are capable of limited escape flight at 45-56 days and sustained flight at 63-70 days of age (Moorman and Grey 1994). Mottled Ducks prefer shallow ponds and are flightless during the spring and summer, when in danger the hen will try to lead predators away from the brood (Elsey, Trosclair, and Linscombe 2004).

The study performed by Scott Durham and Alan Afton on breeding biology of the Mottled Duck, found that aquatic macroinvertebrates are an important food source to mottled ducks during the breeding season. They made this correlation by the observation of farmers flooding rice fields. The ducks apparently did not nest until the fields were flooded, which in turn gave the ducks a proper foraging habitat (Durham and Afton 2006).

The mottled duck has come under scrutiny due to a population concern because of habitat loss from costal marshes and adjoining agricultural land. They have become a priority species in the Gulf Coast Joint Venture of the North American Waterfowl Management Plan and new studies concerning this phenomenon are well underway (Durham and Afton 2006).

Bibliography:

Durham, R. Scott; Afton, Alan D.. Southeastern Naturalist, 2006, Vol. 5 Issue 2, p311-316, 6p; (AN 21940756)

Elsey, Ruth M.; Trosclair III, Phillip L.; Linscombe, Jeb T.. Southeastern Naturalist, 2004, Vol. 3 Issue 3, p381-390, 10p, 2 charts, 1 graph, 1 bw; (AN 14659008)

Moorman, T.,E. Gray. P.,N. Birds of North America: Mottled Duck, No. 81, 1994

Knopf, Alfred, A. National Audubon Society: Field Guide to North American Birds.

1995, Random house, inc. New York.

Bellrose, Frank, C. Ducks, Geese, & Swans of North America. 1980. StackPole

Books, Harrisburg, Pa.

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