Common Teal: Eurasian and American Green-winged Teal and hybrids: an identification challenge
In 1994 the Oregon Bird Records Committee began to review "records of select subspecies that may become full species in the near future." In the list was the Eurasian Green-winged Teal (Anas crecca crecca). This subspecies was given full species status in Europe in 2000, but this change has yet to be adopted by the American Ornithologists' Union.
Several male Eurasian Green-winged Teal have been reported from Oregon in recent winters. In addition, several more individuals have been observed showing combinations of characters belonging to both Eurasian and American types, and are presumed intergrades/hybrids.
I have had several opportunities to observe and photograph vagrant Eurasian Green-winged Teal and presumed hybrids over the past two winters in Oregon. Some birds I first thought to be "pure" Eurasian Green-winged Teal I now believe to be hybrids due to subtle plumage characters I explain here. The existence of apparent hybrids creates a challenge for observers and records committees alike.
There is very little written about hybrid teal and their identification. In fact, there isn't much written about the separation of the American and Eurasian forms. I present here guidelines (based on my limited observations and literature searches) for separating "hybrid" teal from "pure" Eurasian and American Green-winged Teal. This article uses photographs of a single male Eurasian Green-winged Teal and a single male hybrid Eurasian x American Green-winged Teal in Forest Grove, Oregon, on 28 November 2003.
This discussion focuses primarily on males. Females of Eurasian and American Green-winged Teal are difficult to separate in the field. Female hybrids are likely to be impossible to identify, either in the field or in the hand. A brief note on females is included at the end of this article.
Major character 1: horizontal scapular stripe
Eurasian Green-winged Teal: Bold horizontal white stripe from shoulder back to tail. At rest, the scapulars cover the folded wing from above, while the gray feathers of the side of breast cover the wing from below. As a result, the wings of many ducks are not visible when at rest. The lower scapular feathers have a black outer web and a broad white inner web. It is this white inner web of the scapular feathers that produced the horizontal white stripe on the Eurasian Green-winged Teal. Sometimes the lower gray side feathers cover a portion of the white stripe. Usually, however, the stripe is very obvious, and the white is wider than the black.
American Green-winged Teal: The black outer web of the scapular feathers may be visible, but are usually not obvious. The inner webs are brownish gray and do not contrast boldly with the back. Thus, the American form never shows a white scapular stripe.
Hybrid Teal: Often have a white and black horizontal scapular stripe. However, the white is narrow and often restricted primarily to the middle of the sides. In summary, the white stripe is both narrow and short.
Major character 2: vertical white breast bar
American Green-winged Teal: Bold vertical white bar from shoulder downward across the side of the breast.
Eurasian Green-winged Teal: Absolutely no hint of a vertical white bar on the side of the breast.
Hybrid Eurasian x American Green-winged Teal: Often faint vertical white bar from shoulder downward across the side of the breast. May be invisible in the field at some angles.
Major character 3: creamy face markings
Eurasian Green-winged Teal: Bold creamy lines on the face outline the base of the bill and extend over and around the green patch on the side of head, as well as outlining the under side of the green ear patch. The creamy lines are obvious above the green ear patch to well back of the eye.
American Green-winged Teal: A short white line is usually obvious on the under side of the green ear patch, under the eye.
Hybrid Eurasian x American Green-winged Teal: Usually faint creamy lines on the face outline the base of the bill and on the under side of the green ear patch, below the eye.
Minor Supporting Characters:
The following characters may support the identification, but never supercede the three major identification criteria above.
A note on females:
The base color of female American Green-winged Teal is brown. The base color of Eurasian Green-winged Teal is pale. Thus the Eurasian birds appear paler and less heavily marked. Female American Green-winged Teal often have a dark crown, dark line through the eye, dark cheek or ear spot, and pale crescent at the base of the bill. The female Eurasian Green-winged Teal is plainer faced and paler overall. These characters may be visible on a female accompanying an out-of-place male. The color of the upper border of the speculum on the open wing (in flight or flapping in place or stretching) is supposedly the diagnostic mark (see Sibley's field guide) for separating Eursian and American females (but variation and hybrids may make some females unidentifiable).