The Mallard (Anas platyrhynchos) is one of the most active species when it comes to hybridization. This familiar duck species interbreeds with numerous other duck species, including the Mottled Duck (A. fulvigula).
In January 2017, I wrote about Mottled Ducks in North America (see here). This blogpost focused on the genetic divergence between two Mottled Duck populations in Florida and the Western Gulf Coast. I briefly mentioned hybridization with Mallards.
In a recent study, published in The Condor, Robert Ford (Louisiana State University) and colleagues investigate the hybridization dynamics between these duck species in the Western Gulf Coast populations. Using microsatellites, they estimate levels of hybridization between 5 and 8%, which is lower compared to Florida (about 9%).
Why are these levels of interbreeding so low? Probably because Mallards and Mottled Ducks do not meet that often. Mottled Ducks are not migratory and remain all year at the Western Gulf Coast, whearas Mallards do migrate. In addition, Mottled Ducks form pairs in fall, starting as early as August. When the Mallards arrive, most Mottled Ducks have already found a partner. But despite these limited opportunities for hybridization, hybrids do occur. This can probably be explained by such behavioural processes as interspecific nest parasitism and extra pair copulations (see here for an overview in geese). Hybridization might also be due to feral Mallards that have escaped from game breeders.
No Conservation Issue (Yet?)
For now, it is unclear whether duck hybridization in the Western Gulf Coast will be a conservation issue in the future. The most important factor seems to be habitat loss, which could drive Mottled Ducks into urban areas where feral Mallards could welcome them with open arms (or wings)…
Ford, R. J., Selman, W. & Taylor, S. S. (2017). Hybridization between Mottled Ducks (Anas fulvigula maculosa) and Mallards (A. platyrhynchos) in the western Gulf Coast region. The Condor 119, 683-696.
Thanks to Robert Ford for sending me a copy of the paper. This study has been added to the Anseriformes page.