Texas Waterfowl

Mexican Duck

57 and Fredrickson 1981; Heitmeyer and Vohs 1984; Heitmeyer 1985; Whyte and Bolen 1985; Duebbert and Kantrud 1987; Frentress 1987; Weller 1988; Smith et al. 1989; Arnold et al. 1993; Ray and Higgins 1993; Johnson and Rohwer 2000; Drilling et al. 2002; Bogiatto and Karnegis 2006; Stafford et al. 2007; Baar et al. 2008. reproduction: Hochbaum 1944; Bjarvall 1968; Dzubin and Gallop 1972; Bellrose 1980;Talent et al. 1983; Greenwood et al. 1987, 1995; Heitmeyer 1988; Johnson and Grier 1988; Rhymer 1988; Rohwer and Freeman 1989; Lokemoen et al. 1990; Batt et al. 1992; Rotella and Ratti 1992; Dzus and Clark 1997; Johnson and Rohwer 1998; Evard 1999; Stafford et al. 2001; Drilling et al. 2002; Loos and Rohwer 2004. appearance: Bellrose 1980; Krapu 1981; Drilling et al. 2002. MEXICAN DUCK (MEXICAN MALLARD) Anas platyrhynchos diazi Mexican Ducks were once considered a separate species (Anas diazi) and were even endangered due to perceived declines in the US portion of their range. After extensive hybridization with Mallards was documented in the northern portion of their range, the endangered species status was removed. Although hybridization is likely not an issue in the southerly extent of their range, they are also no longer considered to be a distinct species. Genetic evidence, which was not available at the time the species was combined with Mallards, suggests they are more closely related to Mottled Ducks than to Mallards. Most of the information in the account below, including harvest statistics, is from studies of Mexican-like ducks that occur in the northern limit of the range. TEXAS DISTRIBUTION Surveys in the 1970s suggested there were about 250 breeding pairs in the TransPecos . These are conservative estimates, as survey methodology did not use expansion factors to account for nonsurveyed habitats. Wintering Mexican Ducks are most common in the Trans-Pecos region, but there are no estimates of their winter numbers. POPULATION STATUS There are approximately 55,000 Mexican Ducks, including about 5,000 in the United States. Data from Mexico suggest their population increased between 1966 and 2000. RANGE AND HABITATS Mexican Ducks breed in the highlands of interior Mexico, in southeastern Arizona, in southern New Mexico, locally in the Trans-Pecos, and along the Rio Grande from El Paso southeast to Hidalgo County. Breeding pairs frequent rivers, riparian areas, flooded fields, and ponds. They nest on the ground; their nests have been found in wet meadows, dense brush thickets, and thick vegetation near ponds. Nests are typically located near water. Long-term survey data from Mexico indicate migration is not likely. Nonbreeding and wintering individuals are likely nomadic, moving in response to availability of surface water. Wintering Mexican Ducks take advantage of agricultural crops, irrigation water, and depressional wetlands. dabbling ducks 58 REPRODUCTION Mexican Ducks form seasonal pair bonds. Most females are paired in January, and pair bonds dissolve during incubation. Few nests have been found. Average clutch size is likely similar to that of Mallards. Only females care for ducklings. Ducklings are found on creeks, ponds, and irrigation canals. The duration of their fledging period is unknown. APPEARANCE Males and females average 2.3 and 2.0 pounds, respectively. Both sexes closely resemble female Mallards but are notably darker. Females have an orange bill that is splotched with black. Males have yellow bills. In Texas, where the population consists of many hybrids, males often have greenish feathers on their forehead. Their breeding and nonbreeding plumages are similar. Mexican Duck (male). Photograph by Mark W. Lockwood, November 15, 2008, Alpine, Brewster County, Texas. 59 SOURCES introduction: Aldrich and Baer 1970; USFWS 1978; McCracken et al. 2001. texas distribution : Swepston 1979. population status: Rose and Scott 1997; Pérez-Arteaga et al. 2002. range and habitats: Lindsey 1946; Ohlendorf and Patton 1971; Nymeyer 1975; O’Brien 1975; Hubbard 1977; Bellrose 1980; Lockwood and Freeman 2004; Pérez-Arteaga and Gaston 2004. reproduction: Lindsey 1946; O’Brien 1975; Hubbard 1977; Swepston 1979. appearance: Huey 1961; Bellrose 1980; Drilling et al. 2002. MOTTLED DUCK Anas fulvigula Although rates of ingestion of lead pellets (spent lead shot) by Mottled Ducks have declined since regulations were implemented that prohibited hunting waterfowl with toxic shot, their ingestion rate is still among the highest of any North American duck. Ingestion of lead pellets occurs while ducks are foraging ; the shot is either picked up as grit or as a potential food source. From 1998 to 2002, approximately 14 percent of Mottled...