The Waning Reign of the Wetland Architect We Barely Know (Hint: Not a Beaver) Little-appreciated, semiaquatic, and cute-as-hell, muskrats can survive almost anywhere. So where are they? (Brandon Keim for Hakai Magazine)

Since the early 1970s, muskrat populations appeared to have fallen by at least one-half in 34 US states. In a handful of states, the collapse was near-total, coming in between 90 and 99 percent. Muskrats remain fairly common overall—no official population count exists, but it's safe to ballpark within the millions throughout their range—and in some places, they still thrive, with as many lodges per wetland hectare as there are homes in a leafy suburban subdivision; researchers don't fear their extinction, but the overall trend is deeply troubling. It is also mysterious.

Professor Young’s experiments with prairie voles revealed what poets never could: how the brain processes that fluttering feeling in the heart.