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Game-Farm Ancestry Entered North American Mallard Populations in Repeated Waves

Wild male and female mallards together near water
Research · Genetics & genomics

A historical genomics study has reconstructed more than a century of gene flow from captive-bred game-farm mallards into wild mallards (Anas platyrhynchos) across North America. The researchers sampled 664 museum specimens from 1800 to 2020 across the four major flyways and recovered sufficient DNA from 438 of them. They compared the historical record with modern genomic data. The study was published online on 24 July 2026 in Current Biology.

Game-farm ancestry entered wild populations in repeated waves

Game-farm mallards are a domesticated lineage bred specifically for release and sport hunting. Their genetic ancestry first appeared in the historical wild samples during the 1910s and 1920s, when large-scale releases were beginning to be reported in North America. The change did not result from one introgression event — gene flow in which genetic material from the game-farm lineage became incorporated into the wild population — or from a smooth, steady accumulation. Instead, the historical series showed repeated bouts in which game-farm ancestry entered wild populations.

Eastern flyways accumulated far more domestic ancestry

The geographic pattern was strongly uneven. Mallards in the Pacific and Central Flyways have remained largely genetically wild, whereas game-farm ancestry increased and persisted in the Atlantic and Mississippi Flyways. The strongest signals occurred around the Great Lakes and along the northeastern Atlantic coast, regions with a long history of releasing captive-bred mallards.

Extensive mixing was linked to lower genetic diversity

In eastern North America, the authors describe the present pattern as approaching a domestic × wild hybrid swarm: wild and game-farm ancestry have become so extensively mixed that the genetic distinction between the two sources is breaking down within populations. Groups with more game-farm ancestry also had lower nucleotide diversity — less genetic variation among their DNA sequences — while estimated inbreeding increased with the proportion of game-farm ancestry, indicating more genome segments inherited from shared ancestors.

The timing and geography of these genomic changes closely match the history of game-farm releases. The authors therefore conclude that continued stocking is actively reducing the genetic integrity, or “wildness,” of North American mallards in the most affected regions. They argue that the results have direct implications for captive-breeding and release programmes because repeated releases can keep adding domestic ancestry even after extensive mixing has already occurred.

Sources and image credit

  1. McFarland et al. (2026), Current Biology — The dilution effect of stocking and the loss of wildness among North American mallardsPrimary peer-reviewed study, available online 24 July 2026. Historical and modern genomic samples from North American mallards show repeated introgression from game-farm releases, strong geographic differences among flyways, lower diversity in more admixed groups and increasing inbreeding with game-farm ancestry.
  2. PubMed — The dilution effect of stocking and the loss of wildness among North American mallardsBibliographic record confirming the 24 July 2026 article date and publication details.

Image: Glenn D Chambers / U.S. Fish and Wildlife Service Northeast Region — male and female mallards photographed 24 August 2010. Representative image; not birds used in the genomic study. · CC BY 2.0 — https://creativecommons.org/licenses/by/2.0/ · Source

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