Coexisting without competing: How black ducks and mallards may be avoiding competition for winter habitat

American black ducks and mallards have long been subjects of studies because of their prevalence in North America and as harvested species in recreational hunting seasons.

Black ducks have been a species of concern since the 1980s due to steep declines in their abundance, and competition with mallards is one hypothesis explaining the decline of black ducks and their limited recovery.

Wintering black ducks have increased in Atlantic Canada over the last four decades, along with breeding numbers of mallards, and both species are often found in the same habitats.

Read this open access paper on the FACETS website.

In this study we examined the digestive tract morphologies and mercury concentrations of black ducks and mallards wintering in Atlantic Canada, and we related differences in digestive tract morphologies and mercury concentrations to the different ecological niches exploited by these species. Black ducks were studied in coastal and urban habitats, and mallards were studied in coastal habitats.

Coastal black ducks had longer guts and higher mercury concentrations than mallards studied in the same habitats, likely due to the different diets of these two species.

Urban black ducks and coastal mallards had similar gut morphologies and mercury concentrations, likely due to their similar diets.

Black ducks and mallards may be able to avoid competition by exploiting different resources in the same habitats, which results in different gut morphologies and contaminant loads exhibited by these species.

The flexibility of black ducks in their ecological niches may be one reason why they have increased in abundance through winter in Atlantic Canada over the last four decades.

Read the paper — Variation in isotopic niche, digestive tract morphology, and mercury concentrations in two sympatric waterfowl species wintering in Atlantic Canada by Matthew D. English, Gregory J. Robertson, Nelson J. O’Driscoll, Sara J. Klapstein, Liam E. Peck and Mark L. Mallory.