Colorado Independent: The first robin of spring usually warms the heart after a long winter in Colorado, but a study released last week by the National Audubon Society says the red-breasted harbingers have stopped leaving the state in the winter and herald warming of a different kind. Over the past four decades, in late December American Robin counts in Colorado have increased more than 17-fold as migration patterns follow rising temperatures northward. It`s a trend found in a majority of species …