My current birding project is studying the various races of Cackling and Canada Geese (Branta hutchinsii and Branta canadensis). Canada Goose was split into these two species in 2004. There are multiple races of each, so it is a good idea to become familiar with all the different forms in case more splits occur. If nothing else, it adds a bit of a challenge when confronted with a large congregation of geese.
In the Pacific Northwest, there are four races of Canada Goose (Western, Vancouver, Dusky, and Lesser) and three races of Cackling Goose (Taverner’s, Aleutian, and Cackling). The greatest identification challenge seems to be differentiating between Lesser Canada Goose and Taverner’s Cackling Goose. The two overlap in size and color, and different sources give conflicting information about their characteristics. The best field mark on close birds seems to be the shape and relative length of the bills; short and steep on Taverner’s, longer and more sloping on Lesser Canada.
Here are a few websites that you may find helpful in learning the various races of white-cheeked geese.
http://sibleyguides.com/canada_cackling.htm David Sibley’s notes that were written just after the species were split. Good information, but not complete, especially regarding the Lesser Canada/Taverner’s Cackling issue.
http://www.idahobirds.net/identification/white-cheeked/subspecies.htm Harry Krueger’s site. This is a work in progress, but it offers great information on several subspecies.
http://www.dfw.state.or.us/resources/hunting/waterfowl/goose-permits/Goosefieldguide_2ndEdition_final.pdf This 83-page publication from the Oregon Department of Fish and Wildlife is a wealth of information and photographs. Be warned; this publication is intended for hunter education, so some of the photos are of “harvested” birds.
Cackling Cackling Goose (top) and possible Lesser Canada Goose