SUMMARY:
Ross’s Geese and Snow Geese are both white-bodied waterfowl with black wingtips that can be difficult to tell apart. The pair are a great example of what science calls sister species, which occur when a portion of one species takes an evolutionary step away from the rest, resulting in a species split. In this case, genetic studies suggest that the Ross’s Goose branched away from their Snow Goose relatives more than 2 million years ago, possibly because advancing glaciers separated the two populations. After spending millennia in isolation, the Ross’s Goose evolved to be about ⅔ the size of a Snow Goose, with a noticeably shorter neck, smaller bill, and higher-pitched voice too.
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(Content courtesy of birdnote.org.)
