Bird migration has fascinated humans for millennia, and although we’ve come a long way since some authorities seriously entertained the notion that swallows overwintered as torpid animals in crevices, in the mud at the bottom of ponds, or even migrated between the earth and moon (Birkhead 2008), we’re still struggling to discern its evolutionary origins. For most of us born and raised in the northern hemisphere, we were taught (or simply assumed) that the answer was obvious: “our birds” left for warmer southern regions to escape almost certain death in the cold and snowy months of winter (the “northern home hypothesis”). But by the 1980s as Neotropical ornithology rose to prominence, an alternative view, that migrants dispersed out of tropical America to seasonally populate North America, became the dominant paradigm. The fitness advantage generated by the ability to exploit large seasonal pulses of food, combined with depressed population...

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