Increasing Mallards, Decreasing American Black Ducks: More Evidence for Cause and Effect

Habitat use by sympatric female mallards and American black ducks breeding in a forested environment

“…Mallards in southern Ontario, however, currently occupy the most fertile wetlands after competitively excluding black ducks, which now occupy the least fertile wetlands (Merendino et al 1993). Although species-specific use of the four wetland habitats in the present study was similar, mallards tended to use more productive habitats (77 % eme'rgent and scrub-shrub) than did black ducks (5 1 %).…”

Asymmetric Hybridization and Sex-Biased Gene Flow Between Eastern Spot-Billed Ducks (Anas Zonorhyncha) and Mallards (A. Platyrhynchos) in the Russian Far East

“…Mitochondrial (mt) DNA haplotypes are polyphyletic among these taxa, suggesting a recent radiation (Avise et al 1990, McCracken et al 2001, Lavretsky et al 2014, and ongoing hybridization between Mallards and each of the monochromatic species complicates phylogenetic inferences (Heusmann 1974, Hubbard 1977, Avise et al 1990, Dwyer and Baldassarre 1993, Merendino et al 1993, McCracken et al 2001, Pérez-Arteaga et al 2002, Pérez-Arteaga and Gaston 2004, Williams et al 2005a). Lavretsky et al (2014), for example, demonstrated that the posterior support for the NW monochromatic taxa doubled when Mallards were excluded, suggesting a confounding effect of contemporary introgression.…”

“…Once found primarily west of the Mississippi River, environmental degradation (Livezey 1991, Green 1996, Mank et al 2004) and release programs (Heusmann 1974, Soutiere 1986, Hepp et al 1988 caused an expansion of the Mallard's range across North America leading to increased interspecific competition and hybridization with the monochromatic endemics. Growing interactions with Mallards have negatively influenced Black Duck populations since the 1950s (Ankney et al 1987, Avise et al 1990, Dwyer and Baldassarre 1993, Merendino et al 1993, Rhymer 2006), leading to concerns over the possibility of extinction by introgressive hybridization (Rhymer and Simberloff 1996). Moreover, the taxonomy of both Mexican Ducks (Hubbard 1977, Pérez-Arteaga et al 2002 and Mottled Ducks (Bielefeld et al 2010) have gone through various revisions, and continue to be debated.…”

Correlates of behavioural dominance in mallards and American black ducks

“…Upon arriving at the breeding grounds in the spring, black ducks and mallards compete for territories (Seymour 1993). Competition between mallards and black ducks for breeding habitat has rarely been directly observed, but Merendino et al (1993) provided evidence from historical data that mallards have systematically excluded black ducks from highquality breeding habitat in southern Ontario. Furthermore, Merendino & Ankney (1994) showed that, in central Ontario, mallards now occupy the most productive breeding sites and predominate in more productive geographical areas.…”

“…Several hypotheses for the cause of this phenomenon have been proposed, including habitat changes (Heusmann 1974;Conroy et al 1989), over-hunting (Conroy et al 1989), competitive exclusion (Ankney et al 1987Merendino et al 1993) and introgressive hybridization (Ankney et al 1987Rusch et al 1989). These hypotheses are not mutually exclusive, but Ankney et al (1987Ankney et al ( , 1989, Rusch et al (1989), Merendino et al (1993) and Merendino & Ankney (1994) have concluded that hybridization and competition have been the most important factors influencing population dynamics of black ducks and mallards in eastern North America.…”