Prevalent transoceanic fall migration by a 30-gram songbird, the Bobolink

Three North American passerines are known to perform transoceanic flights during their fall migration, with open-water flights ranging in length from 1,700 to 3,400 km. However, little is known about within-population variation of these flights. From 2013 to 2017, I used geolocators to study variation in the fall migratory track of the Bobolink (Dolichonyx oryzivorus) from a population that bred in agricultural grasslands of Vermont, USA. Thirteen of seventeen birds took transoceanic flights during fall migration, ranging in length from 1,098 to 3,536 km (mean +/- SD = 1,969 +/- 6 640); five of these flights were nonstop from North to South America. Bobolinks initiated transoceanic flights between Nova Scotia, Canada, and the central coast of North Carolina, USA, an orthodromic distance of 2,500 km. Mean arrival to 128 latitude in South America was October 17 +/- 17 days (range: September 26-November 26). Neither sex, morphological measurements, nor age significantly explained variation in nonstop flight length.