While looking for current information on whether the ABA has made a decision to grant the "Common" Teal full species status from Green-winged Teal, I came across the following website showing the history of AOU names up to 1998. It's a pretty interesting list. Check it out here.
I now have "Common" Teal on my life list but I'm not sure if I should give it full species status or not. Either way, it's still important to look for subspecies and different plumages in birds, which can be just as exciting as seeing a new species. It is also important because if a species is eventually split based on new evidence, then a record of appearances and ranges has still been kept.
The individual bird that many saw at Hillman Marsh in the spring of 2006 was a textbook example of the Eurasian subspecies with a bold white horizontal stripe along its scapulars, whiter feathers on the femoral tract, and a paler brown on the cheek and auriculars, throat, and forehead than the American subspecies contrasted with bolder white streaks bordering the green face patch. There was some debate about the presence or absence of the white spur at the bird's side. I thought I could detect a slight paleness of the feathers in this area but some birders thought it was a trick of the light and the bird's position (and also considering the distance). This may suggest an earlier hybridization or a hybrid parent.
Based on morphological, genetic, and behavioural differences, many authorities have split the species, including the British. However, AOU is still contesting the split and treating the two forms as conspecific.