Tuesday, November 12, 2013

A Rare and Unusual Hybrid Duck in Stratford

For several years this adult male Northern Pintail X Mallard (the bird on the left in the photo to the left) has returned to Wooster Pond on Freeman Avenue in Stratford where locals provide food for wintering waterfowl.

Waterfowl crossbreed more often than any other family of birds. Scientists have recorded more than 400 hybrid combinations among waterfowl species. Mallards crossbreed with nearly 50 other species, and Wood Ducks hybridize with a surprising 26 other species. Nearly 20 percent of waterfowl hybrid offspring are capable of reproducing, unusual in nature where hybrids are commonly sterile.

In general, hybridization is rare because each waterfowl species has unique characteristics that serve as barriers to interspecies mating. These characteristics include distinct physical attributes, behaviors, life-history requirements, and the unique ecological niche the species occupies. But on the breeding grounds, territories of many waterfowl species overlap, and barriers occasionally break down, presenting opportunities for interspecies mating.

Although this bird seems strange and unique, in North America one of the most common wild hybrids results from Mallard/Pintail breeding. Mallards also commonly crossbreed with Black Ducks, American Wigeon, Northern Shovelers, and Gadwalls.

Beyond creating interesting-looking ducks, hybridization can potentially lead to the extinction of a species. When individuals of two species mate and produce fertile offspring, which then mate with the parent species, this essentially contaminates the pure genes of that species. Mallards are highly aggressive breeders, and several cases involving Mallard hybridization with closely related species present waterfowl biologists with conservation challenges.

This really hits home in Connecticut where Mallards often breed with Black Ducks, which have been on a long-term decline throughout their range. Habitat loss due to agriculture and forestry practices have altered much of the Black Duck’s original breeding habitat and has allowed Mallards to move east (they were originally a western species) where they now frequently interact with Black Ducks. This alteration has allowed Mallards to expand their range, leading to more interaction with Black Ducks and increasing opportunities for hybridization.

Changes to Black Duck migration and wintering habitat have also fostered encroachment by Mallards. Forests that once separated these species have been cleared, giving Mallards more opportunities to interact with Black Ducks during the nonbreeding season. Interspecies interactions on the wintering grounds are important because this is when waterfowl form pair bonds for the upcoming breeding season. This interaction could lead to mixed-species pairing and contribute to the hybridization problem.

Although Mallard/Black Duck hybridization is an ongoing issue, the two species coexist for the most part in Connecticut and by far the greatest threat to Black Duck survival is the loss of suitable nesting and wintering habitat.

This beautiful, but strange looking hybrid reminds us that the fascinating world of birds is a complex and ever-changing natural system. -- Milan Bull, Senior Director of Science and Conservation

Top photo by Frank Mantlik
Bottom photo by Rick Wright

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