Mottled Ducks are the only dabbling ducks that both nest and winter in large numbers along the Gulf Coast (Stutzenbaker 1988). They also are the only non-migratory dabbling ducks in the conterminous U.S. (Bellrose 1980). Two populations of Mottled Ducks occur in North America. One population is a resident of peninsular Florida and the other is a resident of the Gulf Coast from Alabama westward to Veracruz, Mexico (Moorman & Gray 1994).
Mottled Ducks were considered to be conspecific with American Black Ducks (Anas rubripes), which they closely resemble, until the 1870s (Bent 1923). Like American Black Ducks, male and female Mottled Ducks have similar plumage and are best differentiated by bill coloration (Bellrose 1980).
DISTRIBUTION: Mottled Ducks are common in the extensive marshes located between Galveston Bay and Sabine Lake, and locally common to uncommon along the remainder of the Texas coast (Oberholser 1974, Stutzenbaker 1988). They nest in all coastal counties, in most first-tier inland counties, and in the coastal prairies (Oberholser 1974, Hobaugh et al. 1989). Notably different than range maps in Oberholser (1974) or Stutzenbaker (1988), TBBAP data suggest Mottled Ducks breed several counties inland along the Rio Grande, with a brood sighting near the city of Zapata (26099-H2) being the most westward confirmed record. TBBAP data also suggest possible breeding in Frio (28099-H1), La Salle (28099-C2), and Dimmit Counties (28099-E4).
Probable breeding accounts reported by TBBAP in northeast Texas are in an area where attempts were made to propagate Mottled Ducks, and where past sightings have been documented (Oberholser 1974, Stutzenbaker 1988). In one northeast Texas quadrangle (33095-A1), Mottled Ducks were recorded for two consecutive years during TBBAP surveys.
SEASONAL OCCURRENCE: Most Mottled Ducks nest between February and July (Grand 1992, Stutzenbaker 1988), with the average (or peak) date of nest initiations occurring in March, April, or May (Baker 1983, Grand 1992, Stieglitz & Wilson 1968). Year to year variation in timing of peak nest initiations can exceed 60 days (Grand 1992). Low water levels in late winter and spring are correlated with late nest initiation peaks (Grand 1992). Extreme dates reported for nesting activities include an early February nest in Chambers County and a Christmas Eve brood sighting in Jefferson County (Stutzenbaker 1988).
BREEDING HABITAT: In the coastal regions of Texas and Louisiana Mottled Ducks nest primarily in dense stands of cordgrass (Spartina spp.) (Baker 1983, Stutzenbaker 1988). Other grasses and bush-forming plants also are utilized as nesting cover, but to a lesser extent (Engeling 1950, Stutzenbaker 1988). Mottled Duck nests are typically “built up” several centimeters from the ground with plant material or suspended above ground in dense stands of cordgrass (Engeling 1950, Rorabaugh & Zwank 1983). Over-water nests are extremely rare; in fact, Stutzenbaker (1988) documented only one. On 18 June 1991 a floating nest was found during TBBAP surveys; it was built on dead vegetation, water hyacinth (Eichhornia crassipes) and debris lodged at the intake to a pump station (26097-A7) located on the Rio Grande (W. MacWhorter, pers. comm.).
Mottled Ducks lay 8 to 12 eggs, which are covered with down and/or grass litter when females take incubation breaks (Moorman & Gray 1994). Eggs range in color from pale white to dull olive, but a single clutch will contain only eggs of one color (Moorman & Gray 1994, Johnson et al. 1996). Eggs are incubated approximately 26 days, and they hatch synchronously (Engeling 1950, Stutzenbaker 1988). During the time that eggs are hatching, some females will perform distraction displays in attempts to lead predators away from their nests (W. P. Johnson, pers. obs.).
Mottled Duck nests are typically dispersed, as the maximum density recorded in Texas is only 1 nest/1.4 hectares (1 nest/3.5 acres) (Stutzenbaker 1988). Higher nest densities have been documented only on dredge-spoil islands in Florida and Louisiana (Stieglitz & Wilson 1968, Holbrook 1997). Nest parasitism (one female laying eggs in another female’s nest) has only been reported for Mottled Ducks nesting on islands, and was probably the result of high nest densities (Johnson et al. 1996).
STATUS: Annual surveys of breeding Mottled Ducks are conducted on several national wildlife refuges that are located on the Texas coast. Densities of pairs fluctuate widely from year to year, with low years partly attributable to drought conditions (Neaville 1996). Similar conclusions regarding the impact of drought have been drawn in Florida (Moorman & Gray 1994). Analysis of Christmas Bird Count data suggest Mottled Duck populations are not declining (McKenzie et al. 1988).
The most serious threat facing Mottled Ducks is degradation and loss of habitat (Stutzenbaker 1988). In Texas, factors contributing to loss of habitat include agriculture, urbanization, drainage, marsh subsidence, saltwater intrusion, and the spread of introduced species (Stutzenbaker 1988, Morton & Paine 1990). Saltwater encroachment into wetlands that range from fresh to moderately brackish probably affects growth and survival of ducklings (Moorman et al. 1991). Encroachment of Chinese tallow (Sapium sebiferum), an exotic tree, into nesting habitat probably leads to abandonment of nesting areas (Stutzenbaker 1988). Though it is not yet a serious problem in Texas, Mottled Duck hybridization with feral Mallards (Anas platyrhynchos) has the potential to increase with continued human population growth along the coast (Moorman & Gray 1994).
Text by William P. Johnson (ca. 1998)
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