Calendars remind us that spring is officially here as of March 20, but some bird species have been signaling its arrival for the past few weeks. American robins were long considered by casual birders in the upper reaches of the U.S. to be the harbinger of spring, and for many that remains the case. But long ago, robins began adapting to colder winter climates, and now flocks of them can be found living year-round throughout the Upper Midwest, Canada and even Alaska. I’ve seen robins throughout this winter, usually perched in some sort of an ornamental fruit tree, feasting on the remaining vestiges of last fall’s berry and apple crops.