A new study, published in The Condor, has examined the outlook for the little-known Mottled Duck, a close relative of the more familiar Mallard.
Mallard is one of a group of closely related waterfowl species of the genus Anas, many of which are far less common. Interbreeding with Mallards A platyrhynchos can threaten the genetic distinctiveness of those other species and consequently cause concern for their conservation. One such example is Mottled Duck A fulvigula, a species specially adapted for life in the Gulf Coast marshes of the United States. The new study found that while hybridisation rates are currently low between Mottled Duck and Mallard, human activity could cause them to rise in the future.
There are two disjunct populations of Mottled Duck: one is found in Florida and the other along the coast between Alabama and north-east Mexico. In Florida, hybridisation between domesticated Mallards and Mottled Ducks is a cause for concern, but the degree of crossbreeding in the western Gulf Coast region was less well known.
Louisiana State University’s Robert Ford and his colleagues took blood samples from Mottled Ducks captured on the coast of Louisiana in 2011-14, supplementing them with samples from Mottled Ducks and Mallards from Texas, Alabama and Mississippi. Analysing the birds’ DNA, they found that the hybridisation rate in the western Gulf Coast region is currently only 5-8 per cent, a level lower than what has been documented in Florida.
However, that doesn’t mean the western Gulf population is completely in the clear. The two species currently have little opportunity to interact in the region during the breeding season: Mottled Ducks nest in coastal marshes while most Mallards are migratory and breed outside the region. However, the ongoing loss of marsh habitat could force Mottled Ducks to move into urban and suburban areas, where they will be more likely to encounter resident Mallards. To prevent future problems, Ford and his team recommend ongoing monitoring of hybridisation in the region and better protection of coastal marsh habitat.
Ford explained: “The biggest challenge in collecting samples was finding moulting Mottled Ducks, which we collected during bird banding operations in the summer. Identifying birds as either Mottled Ducks or Mallards in the summer can be difficult, but most of our banders had years of experience and we did not have many problems. In the future, I would like to see improvements in the methods to identify hybrids, such as more precise techniques that could identify gene combinations unique to hybrids.”
Waterfowl expert Gary Hepp added: “Hybridisation between Mottled Ducks and Mallards is a significant conservation concern in the southern US. Ford et al recommend programmes to monitor future changes in hybridisation, and a proactive management approach similar to Florida’s that controls the number of non-migratory Mallards while prohibiting future releases of game farm Mallards may also be prudent.”
Ford R J, Selman W & Taylor SS. 2017. Hybridization between Mottled Ducks (Anas fulvigula maculosa) and Mallards (A. platyrhynchos) in the western Gulf Coast region. The Condor 119: 683-696. DOI: https://doi.org/10.1650/CONDOR-17-18.1