Eurasian Wigeon Hybrid Controversy

At the BirdForum members are debating whether or not the slight green eye patch on the Eurasian Wigeon denotes a hybrid, or if it is a common feature of some Eurasian Wigeons.

Related Resources Wigeons Types of Birds

Apparently Sibley, an authoritative voice in the American birding community, also places Eurasian Wigeons with a brown head and slight green patch on the head in the hybrid category. (note: The Eurasian Wigeon is an uncommon to rare visitor to the United States.)

Members of the BirdForum participating in the discussion question that placement. They cite a variety of reasons, including personal observations of many Eurasian Wigeons over long periods of time, as reasons for their disagreement with the placement. Because the Eurasian Wigeon is a native bird to Europe, and members of the BirdForum reporting their observations are from Europe, their observational reports need to be respected.

One rationale for discounting the hypothesis that Eurasian Wigeons with a green patch are hybrids rests on personal observations. The logic of the position builds on the idea of the mathematical probability that so large a number of green-patch Eurasian Wigeons could be hybrids.

Additionally, members note that reports of Eurasian Wigeons with a green patch may be under-observed, because the green patch only becomes visible under certain light conditions, in conjunction with the angle of the observer's view of the wigeon's head.

BirdForum members stand on fairly strong ground with that position. Consider the following four pictures, divided into two separate sets.

Each set consists of two profliles of the duck's face. Two sets mean both sides of the face are photographed. Each picture in the set is a profile of the wigeon, photographed at different angles, and in different light conditions.

Picture number one is the Eurasian Wigeon showing a small green patch above the eye.


Picture two is a profile of the same side of the face, photographed at a different angle and under different light conditions. No apparent green patch is showing above the eye, whereas it was visible in the previous picture.


Picture three is a profile of the opposite side of the face of the same Eurasian Wigeon. The photograph shows how the light conditions when the photograph was taken, along with the angle of the camera lens in relation to the wigeon's head, make it appear as if there is no green patch above the eye.


The profile for picture four is the same Eurasian Wigeon, this time on land. The particular angle of the camera and the light conditions (the clouds came out) reveals a green patch above the eye, whereas it was not visible in the previous picture.

This small comparative case study suggests support for the hypothesis that "light conditions and the angle the picture was taken in relation to the duck's head" accounts for a natural greenish hue on the face of some Eurasian Wigeons. Profiles of each side of the wigeon's head, depending on the light conditions, could either show, or not show, the green patch above the eye.

This brief review does not address the question of whether or not the green patch is a result of hybridization.

Questions about potential genetic differences between Eurasian Wigeons with and without green patches on the head remain unsolved. Is there a genetic possibility for so many different Eurasion Wigeons to potentially share only one specific physical hybrid characteristic, the slight green eye patch? Some forum members think that is a very small possibility, although none claim a background in genetics.

Can Eurasian/American Wigeon hybrids potentially receive only one dominant gene from the American Wigeon stock? Would future generations of these hypothetical hybrids pass on other dominant genes or only this particular gene? The question remains unanswered.

Also left unsaid were other plausible non-hybrid hypotheses that might better explain the presence or absence of a green patch on the side of the Eurasian Wigeon's face. For example, one might hypothesize that Eurasian Wigeons share a genetic characteristic creating the possibility of some having a green eye patch, depending on whether the gene is turned on or off.

It might be equally reasonable to assume that the presence of a "green patch" gene, and its physical appearance, are further dependent on environmental factors such as food source. For example, Eurasian Wigeon's are primarily herbaceous ducks. It might be reasonable to hypothesize that chlorophyll levels in a wigeon's food source influence the presence of green patch.

© 2008. Patricia A. Michaels