Presumed Gadwall x Green-winged Teal hybrid. Photograph by the author.
While visiting the Marion Water Treatment Plant on December 20, 2017, I noticed an interesting duck. The outing started as usual by my climbing up on adjacent compost piles to view the various species of ducks that favor these retention ponds, such as Gadwalls, American Wigeons, American Black Ducks, Mallards, Northern Shovelers, and Green-winged Teal. As I scanned the ducks, a bird that I almost passed off as a Green-winged Teal caught my attention. Further examination of this bird revealed that, although it clearly had a lineage that included a Green-winged Teal, it was not a "pure" Green-winged Teal; there were other genes in the mix.
The first thing I noticed was that the bird was larger than the typical Green-winged Teal in the pond, but it was smaller than the other nearby dabblers and more nearly the size of the shovelers. The bird lacked a vertical white line between the side and chest, which would typically be present on the American subspecies of the Green-winged Teal. It also lacked the horizontal white line along the side, which one would expect to see on the Eurasian or "Common" Teal. The creamy white patch on the undertail coverts that is typical of Green-winged Teal was also much subdued and mostly replaced with black.
Before describing the features that made me conclude that the bird was probably a hybrid Gadwall x Green-winged Teal, I want to describe some of the other species that I considered and why I rejected them as possible parents of this bird. I considered both American and Eurasian wigeon as possibilities, however the complete lack of any warm-brown coloration on the body eliminated American Wigeon. Further investigation of these wigeon hybrids also showed that most exhibit traces of light blue on the bill, which this bird did not have.
The closest contender then became Northern Pintail. From behind, the gray on the duck's body crept up the neck and onto the back of the head, which was suggestive of a male pintail. The smaller than average patch of creamy white on the undertail coverts also suggested the possibility of an intermediate feature between Green-winged Teal and Northern Pintail, as did the dull gray on the body and upper wing feathers. Other features were inconsistent with pintail, however, which made me conclude that this species was not one of the parents. The head shape of the hybrid was blocky, and did not in any way resemble the elegance of a pintail's head and long, slender neck. The tail was also average size for a dabbling duck, not slightly elongated as one might expect if there were pintail genes involved. The clincher for removing this species as a possibility was the white in the tertials of this bird, a feature lacking in Northern Pintail and Green-winged Teal.
The overall appearance of this bird was perfectly intermediate between a Gadwall and a Green-winged Teal. Even the size of the bird was intermediate between the two species. The head shape closely resembled that of a Gadwall, but plainly showed the pattern of a male Green-winged Teal. The back, much of the wing, and body coloration, also seemed to be intermediate between the two: a bit warmer in color than the average Green-winged Teal and grayer than a male Gadwall. The cream-colored patch near the vent was subdued when compared to a Green-winged Teal, and much of it was replaced with black as in a typical Gadwall. Perhaps the most interesting feature of this bird was its wings. Most of the gray portions of the upper wings of the hybrid were typical of both species; however, the pure white secondaries with rufous brown coverts above clearly indicated its Gadwall origin, and a small portion of iridescent green on the secondaries adjacent to the white feathering suggested Green-winged Teal.
On a return trip to the Water Treatment Plant on January 27, 2018, I was amazed to see that the hybrid was still present. These ponds had frozen over completely in early January, so it must have departed temporarily and then returned later for more tasty sewage. On my second visit, I observed the hybrid quarreling with a male Gadwall over a female, but it was visibly overpowered by its larger competitor. The bird vocalized during this exchange and, interestingly, had the nasal quacks of a Gadwall. The bird was still present on January 29.
Gadwall x Green-winged Teal hybrids are apparently rare, although not unprecedented. There is significant range overlap in their breeding ranges. Both species readily breed in prairie regions throughout Canada and the western United States. Both species are also ground breeders that will nest in brush and tall grasses. The greatest barrier to crossbreeding between these two species would seem to be size variation between the two, which to me, would suggest that a drake Gadwall and a hen Green-winged Teal were the parents. Perhaps it's not the flashiest hybrid waterfowl, but incredibly interesting nonetheless.