It was the summer of animals gone weird. Alaskan salmon swam up rivers they weren’t born in, their native streams reduced to trickles. Scores of subtropical species, including seahorses and leatherback turtles, migrated into waters off northern England and Scotland. Polar bears were marooned on a remote Arctic island as large patches of what was normally sea ice melted into water. Hundreds of thousands of seabirds failed to breed. The culprit for all this odd animal behavior? A Northern fever: from Alaska to Norway, meteorologists measured record-setting spring and summer temperatures.