Green-winged Teals - American and Eurasian compared

The Green-winged Teal, Anas crecca, is treated by the AOU as a single species, with 3 named subspecies. The birds we see regularly are have a vertical white bar on the flank towards the breast are the subspecies Anas crecca carolinensis, perhaps better called the American Green-winged Teal. Some examples below.

The iridescent green swath and the green wing patch can also glow purple:

Rarely we get to see a male Green-winged Teal that lacks the white vertical bar, instead showing a variable horizontal white bar on the flank just below the scapulars. Such birds often show a more distinct white line extending as an arc around the green swath and back to the nape. These birds are often referred to as the subspecies called Common Teal, a.k.a. Eurasian Green-winged Teal, Anas crecca crecca. Note the black line on the flank just below the white bar: 

Las Gallinas, San Rafael - Pond #3 - 12/22/2007

We once saw a Green-winged Teal that lacked a white stripe, which my friend Don Reinberg christened as the "No-stripe Teal". Sibley suggests that these birds are likely examples of the Common Teal, with the horizontal bar hidden by overlying lower scapulars:

Las Gallinas, San Rafael - Pond #1 - 12-22-2007

I've been exploring the wonderful 2-volume work by Guy Baldassarre, Ducks, Geese and Swans of North America. Baldassarre strongly feels the Green-winged Teal should be split, in agreement with European authorities, based both on phenotypic features and a significant 6% divergence in DNA.

All of the above photos were taken at the Las Gallinas ponds in San Rafael.

Here's another Common Teal, right in my home town of Mill Valley, CA.

Gem Pond, Mill Valley, CA. 12/29/2015